Framework for Telepresence Multi-Streams
draft-ietf-clue-framework-19
The information below is for an old version of the document.
| Document | Type |
This is an older version of an Internet-Draft that was ultimately published as RFC 8845.
|
|
|---|---|---|---|
| Authors | Mark Duckworth , Andrew Pepperell , Stephan Wenger | ||
| Last updated | 2014-12-11 | ||
| Replaces | draft-romanow-clue-framework | ||
| RFC stream | Internet Engineering Task Force (IETF) | ||
| Formats | |||
| Reviews | |||
| Additional resources | Mailing list discussion | ||
| Stream | WG state | WG Document | |
| Document shepherd | Mary Barnes | ||
| IESG | IESG state | Became RFC 8845 (Proposed Standard) | |
| Consensus boilerplate | Unknown | ||
| Telechat date | (None) | ||
| Responsible AD | (None) | ||
| Send notices to | (None) |
draft-ietf-clue-framework-19
CLUE WG M. Duckworth, Ed.
Internet Draft Polycom
Intended status: Standards Track A. Pepperell
Expires: June 11, 2015 Acano
S. Wenger
Vidyo
December 11, 2014
Framework for Telepresence Multi-Streams
draft-ietf-clue-framework-19.txt
Abstract
This document defines a framework for a protocol to enable devices
in a telepresence conference to interoperate. The protocol enables
communication of information about multiple media streams so a
sending system and receiving system can make reasonable decisions
about transmitting, selecting and rendering the media streams.
This protocol is used in addition to SIP signaling for setting up a
telepresence session.
Status of this Memo
This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF). Note that other groups may also distribute
working documents as Internet-Drafts. The list of current
Internet-Drafts is at http://datatracker.ietf.org/drafts/current/.
Internet-Drafts are draft documents valid for a maximum of six
months and may be updated, replaced, or obsoleted by other
documents at any time. It is inappropriate to use Internet-Drafts
as reference material or to cite them other than as "work in
progress."
This Internet-Draft will expire on June 11, 2015.
Copyright Notice
Copyright (c) 2013 IETF Trust and the persons identified as the
document authors. All rights reserved.
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This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents
(http://trustee.ietf.org/license-info) in effect on the date of
publication of this document. Please review these documents
carefully, as they describe your rights and restrictions with
respect to this document. Code Components extracted from this
document must include Simplified BSD License text as described in
Section 4.e of the Trust Legal Provisions and are provided without
warranty as described in the Simplified BSD License.
Table of Contents
1. Introduction...................................................3
2. Terminology....................................................4
3. Definitions....................................................4
4. Overview & Motivation..........................................7
5. Overview of the Framework/Model................................9
6. Spatial Relationships.........................................14
7. Media Captures and Capture Scenes.............................16
7.1. Media Captures...........................................16
7.1.1. Media Capture Attributes............................17
7.2. Multiple Content Capture.................................22
7.2.1. MCC Attributes......................................23
7.3. Capture Scene............................................28
7.3.1. Capture Scene attributes............................31
7.3.2. Capture Scene View attributes.......................32
7.3.3. Global View List....................................32
8. Simultaneous Transmission Set Constraints.....................34
9. Encodings.....................................................36
9.1. Individual Encodings.....................................36
9.2. Encoding Group...........................................37
9.3. Associating Captures with Encoding Groups................38
10. Consumer's Choice of Streams to Receive from the Provider....39
10.1. Local preference........................................42
10.2. Physical simultaneity restrictions......................42
10.3. Encoding and encoding group limits......................42
11. Extensibility................................................43
12. Examples - Using the Framework (Informative).................43
12.1. Provider Behavior.......................................43
12.1.1. Three screen Endpoint Provider.....................43
12.1.2. Encoding Group Example.............................50
12.1.3. The MCU Case.......................................51
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12.2. Media Consumer Behavior.................................52
12.2.1. One screen Media Consumer..........................52
12.2.2. Two screen Media Consumer configuring the example..53
12.2.3. Three screen Media Consumer configuring the example53
12.3. Multipoint Conference utilizing Multiple Content Captures54
12.3.1. Single Media Captures and MCC in the same
Advertisement..............................................54
12.3.2. Several MCCs in the same Advertisement.............57
12.3.3. Heterogeneous conference with switching and
composition................................................58
12.3.4. Heterogeneous conference with voice activated
switching..................................................65
13. Acknowledgements.............................................68
14. IANA Considerations..........................................68
15. Security Considerations......................................68
16. Changes Since Last Version...................................70
17. Normative References.........................................77
18. Informative References.......................................78
19. Authors' Addresses...........................................79
1. Introduction
Current telepresence systems, though based on open standards such
as RTP [RFC3550] and SIP [RFC3261], cannot easily interoperate with
each other. A major factor limiting the interoperability of
telepresence systems is the lack of a standardized way to describe
and negotiate the use of the multiple streams of audio and video
comprising the media flows. This document provides a framework for
protocols to enable interoperability by handling multiple streams
in a standardized way. The framework is intended to support the
use cases described in Use Cases for Telepresence Multistreams
[RFC7205] and to meet the requirements in Requirements for
Telepresence Multistreams [RFC7262].
The basic session setup for the use cases is based on SIP [RFC3261]
and SDP offer/answer [RFC3264]. In addition to basic SIP & SDP
offer/answer, CLUE specific signaling is required to exchange the
information describing the multiple media streams. The motivation
for this framework, an overview of the signaling, and information
required to be exchanged is described in subsequent sections of
this document. Companion documents describe the signaling details
[I-D.ietf-clue-signaling] and the data model [I-D.ietf-clue-data-
model-schema].
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2. Terminology
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in
this document are to be interpreted as described in RFC 2119
[RFC2119].
3. Definitions
The terms defined below are used throughout this document and
companion documents and they are normative. In order to easily
identify the use of a defined term, those terms are capitalized.
Advertisement: a CLUE message a Media Provider sends to a Media
Consumer describing specific aspects of the content of the media,
and any restrictions it has in terms of being able to provide
certain Streams simultaneously.
Audio Capture: Media Capture for audio. Denoted as ACn in the
examples in this document.
Capture: Same as Media Capture.
Capture Device: A device that converts physical input, such as
audio, video or text, into an electrical signal, in most cases to
be fed into a media encoder.
Capture Encoding: A specific encoding of a Media Capture, to be
sent by a Media Provider to a Media Consumer via RTP.
Capture Scene: a structure representing a spatial region captured
by one or more Capture Devices, each capturing media representing a
portion of the region. The spatial region represented by a Capture
Scene MAY or may not correspond to a real region in physical space,
such as a room. A Capture Scene includes attributes and one or
more Capture Scene Views, with each view including one or more
Media Captures.
Capture Scene View (CSV): a list of Media Captures of the same
media type that together form one way to represent the entire
Capture Scene.
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CLUE-capable device: A device that supports the CLUE data channel
[I-D.ietf-clue-datachannel], the CLUE protocol [I-D.ietf-clue-
protocol] and the principles of CLUE negotiation, and wishes to
upgrade the call to CLUE-enabled status.
CLUE-enabled call: A call in which two CLUE-capable devices have
successfully negotiated support for a CLUE data channel in SDP. A
CLUE-enabled call is not necessarily immediately able to send CLUE-
controlled media; negotiation of the data channel and of the CLUE
protocol must complete first. Calls between two CLUE-capable
devices which have not yet successfully completed negotiation of
support for the CLUE data channel in SDP are not considered CLUE-
enabled.
Conference: used as defined in [RFC4353], A Framework for
Conferencing within the Session Initiation Protocol (SIP).
Configure Message: A CLUE message a Media Consumer sends to a Media
Provider specifying which content and media streams it wants to
receive, based on the information in a corresponding Advertisement
message.
Consumer: short for Media Consumer.
Encoding or Individual Encoding: a set of parameters representing a
way to encode a Media Capture to become a Capture Encoding.
Encoding Group: A set of encoding parameters representing a total
media encoding capability to be sub-divided across potentially
multiple Individual Encodings.
Endpoint: A CLUE capable-device which is the logical point of final
termination through receiving, decoding and rendering, and/or
initiation through capturing, encoding, and sending of media
streams. An endpoint consists of one or more physical devices
which source and sink media streams, and exactly one [RFC4353]
Participant (which, in turn, includes exactly one SIP User Agent).
Endpoints can be anything from multiscreen/multicamera rooms to
handheld devices.
Global View: A set of references to one or more Capture Scene Views
of the same media type that are defined within scenes of the same
advertisement. A Global View is a suggestion from the Provider to
the Consumer for which CSVs provide a complete representation of
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the simultaneous captures provided by the Provider, across multiple
scenes.
Global View List: A list of Global Views included in an
Advertisement. A Global View List may include Global Views of
different media types.
MCU: Multipoint Control Unit (MCU) - a CLUE-capable device that
connects two or more endpoints together into one single multimedia
conference [RFC5117]. An MCU includes an [RFC4353] like Mixer,
without the [RFC4353] requirement to send media to each
participant.
Media: Any data that, after suitable encoding, can be conveyed over
RTP, including audio, video or timed text.
Media Capture: a source of Media, such as from one or more Capture
Devices or constructed from other Media streams.
Media Consumer: a CLUE-capable device that intends to receive
Capture Encodings
Media Provider: a CLUE-capable device that intends to send Capture
Encodings
Multiple Content Capture (MCC): A Capture that mixes and/or
switches other Captures of a single type. (E.g. all audio or all
video.) Particular Media Captures may or may not be present in the
resultant Capture Encoding depending on time or space. Denoted as
MCCn in the example cases in this document.
Plane of Interest: The spatial plane containing the most relevant
subject matter.
Provider: Same as Media Provider.
Render: the process of generating a representation from media, such
as displayed motion video or sound emitted from loudspeakers.
Simultaneous Transmission Set: a set of Media Captures that can be
transmitted simultaneously from a Media Provider.
Single Media Capture: A capture which contains media from a single
source capture device, e.g. an audio capture from a single
microphone, a video capture from a single camera.
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Spatial Relation: The arrangement in space of two objects, in
contrast to relation in time or other relationships.
Stream: a Capture Encoding sent from a Media Provider to a Media
Consumer via RTP [RFC3550].
Stream Characteristics: the media stream attributes commonly used
in non-CLUE SIP/SDP environments (such as: media codec, bit rate,
resolution, profile/level etc.) as well as CLUE specific
attributes, such as the Capture ID or a spatial location.
Video Capture: Media Capture for video. Denoted as VCn in the
example cases in this document.
Video Composite: A single image that is formed, normally by an RTP
mixer inside an MCU, by combining visual elements from separate
sources.
4. Overview & Motivation
This section provides an overview of the functional elements
defined in this document to represent a telepresence system. The
motivations for the framework described in this document are also
provided.
Two key concepts introduced in this document are the terms "Media
Provider" and "Media Consumer". A Media Provider represents the
entity that sends the media and a Media Consumer represents the
entity that receives the media. A Media Provider provides Media in
the form of RTP packets, a Media Consumer consumes those RTP
packets. Media Providers and Media Consumers can reside in
Endpoints or in Multipoint Control Units (MCUs). A Media Provider
in an Endpoint is usually associated with the generation of media
for Media Captures; these Media Captures are typically sourced
from cameras, microphones, and the like. Similarly, the Media
Consumer in an Endpoint is usually associated with renderers, such
as screens and loudspeakers. In MCUs, Media Providers and
Consumers can have the form of outputs and inputs, respectively,
of RTP mixers, RTP translators, and similar devices. Typically,
telepresence devices such as Endpoints and MCUs would perform as
both Media Providers and Media Consumers, the former being
concerned with those devices' transmitted media and the latter
with those devices' received media. In a few circumstances, a
CLUE-capable device includes only Consumer or Provider
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functionality, such as recorder-type Consumers or webcam-type
Providers.
The motivations for the framework outlined in this document
include the following:
(1) Endpoints in telepresence systems typically have multiple Media
Capture and Media Render devices, e.g., multiple cameras and
screens. While previous system designs were able to set up calls
that would capture media using all cameras and display media on all
screens, for example, there was no mechanism that can associate
these Media Captures with each other in space and time.
(2) The mere fact that there are multiple capturing and rendering
devices, each of which may be configurable in aspects such as zoom,
leads to the difficulty that a variable number of such devices can
be used to capture different aspects of a region. The Capture
Scene concept allows for the description of multiple setups for
those multiple capture devices that could represent sensible
operation points of the physical capture devices in a room, chosen
by the operator. A Consumer can pick and choose from those
configurations based on its rendering abilities and inform the
Provider about its choices. Details are provided in section 7.
(3) In some cases, physical limitations or other reasons disallow
the concurrent use of a device in more than one setup. For
example, the center camera in a typical three-camera conference
room can set its zoom objective either to capture only the middle
few seats, or all seats of a room, but not both concurrently. The
Simultaneous Transmission Set concept allows a Provider to signal
such limitations. Simultaneous Transmission Sets are part of the
Capture Scene description, and discussed in section 8.
(4) Often, the devices in a room do not have the computational
complexity or connectivity to deal with multiple encoding options
simultaneously, even if each of these options is sensible in
certain scenarios, and even if the simultaneous transmission is
also sensible (i.e. in case of multicast media distribution to
multiple endpoints). Such constraints can be expressed by the
Provider using the Encoding Group concept, described in section 9.
(5) Due to the potentially large number of RTP flows required for a
Multimedia Conference involving potentially many Endpoints, each of
which can have many Media Captures and media renderers, it has
become common to multiplex multiple RTP media flows onto the same
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transport address, so to avoid using the port number as a
multiplexing point and the associated shortcomings such as
NAT/firewall traversal. While the actual mapping of those RTP
flows to the header fields of the RTP packets is not subject of
this specification, the large number of possible permutations of
sensible options a Media Provider can make available to a Media
Consumer makes a mechanism desirable that allows to narrow down the
number of possible options that a SIP offer-answer exchange has to
consider. Such information is made available using protocol
mechanisms specified in this document and companion documents,
although it should be stressed that its use in an implementation is
OPTIONAL. Also, there are aspects of the control of both Endpoints
and MCUs that dynamically change during the progress of a call,
such as audio-level based screen switching, layout changes, and so
on, which need to be conveyed. Note that these control aspects are
complementary to those specified in traditional SIP based
conference management such as BFCP. An exemplary call flow can be
found in section 5.
Finally, all this information needs to be conveyed, and the notion
of support for it needs to be established. This is done by the
negotiation of a "CLUE channel", a data channel negotiated early
during the initiation of a call. An Endpoint or MCU that rejects
the establishment of this data channel, by definition, does not
support CLUE based mechanisms, whereas an Endpoint or MCU that
accepts it is REQUIRED to use it to the extent specified in this
document and its companion documents.
5. Overview of the Framework/Model
The CLUE framework specifies how multiple media streams are to be
handled in a telepresence conference.
A Media Provider (transmitting Endpoint or MCU) describes specific
aspects of the content of the media and the media stream encodings
it can send in an Advertisement; and the Media Consumer responds to
the Media Provider by specifying which content and media streams it
wants to receive in a Configure message. The Provider then
transmits the asked-for content in the specified streams.
This Advertisement and Configure typically occur during call
initiation, after CLUE has been enabled in a call, but MAY also
happen at any time throughout the call, whenever there is a change
in what the Consumer wants to receive or (perhaps less common) the
Provider can send.
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An Endpoint or MCU typically act as both Provider and Consumer at
the same time, sending Advertisements and sending Configurations in
response to receiving Advertisements. (It is possible to be just
one or the other.)
The data model is based around two main concepts: a Capture and an
Encoding. A Media Capture (MC), such as audio or video, has
attributes to describe the content a Provider can send. Media
Captures are described in terms of CLUE-defined attributes, such as
spatial relationships and purpose of the capture. Providers tell
Consumers which Media Captures they can provide, described in terms
of the Media Capture attributes.
A Provider organizes its Media Captures into one or more Capture
Scenes, each representing a spatial region, such as a room. A
Consumer chooses which Media Captures it wants to receive from the
Capture Scenes.
In addition, the Provider can send the Consumer a description of
the Individual Encodings it can send in terms of identifiers which
relate to items in SDP.
The Provider can also specify constraints on its ability to provide
Media, and a sensible design choice for a Consumer is to take these
into account when choosing the content and Capture Encodings it
requests in the later offer-answer exchange. Some constraints are
due to the physical limitations of devices--for example, a camera
may not be able to provide zoom and non-zoom views simultaneously.
Other constraints are system based, such as maximum bandwidth.
The following diagram illustrates the information contained in an
Advertisement.
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...................................................................
. Provider Advertisement +--------------------+ .
. | Simultaneous Sets | .
. +------------------------+ +--------------------+ .
. | Capture Scene N | +--------------------+ .
. +-+----------------------+ | | Global View List | .
. | Capture Scene 2 | | +--------------------+ .
. +-+----------------------+ | | +----------------------+ .
. | Capture Scene 1 | | | | Encoding Group N | .
. | +---------------+ | | | +-+--------------------+ | .
. | | Attributes | | | | | Encoding Group 2 | | .
. | +---------------+ | | | +-+--------------------+ | | .
. | | | | | Encoding Group 1 | | | .
. | +----------------+ | | | | parameters | | | .
. | | V i e w s | | | | | bandwidth | | | .
. | | +---------+ | | | | | +-------------------+| | | .
. | | |Attribute| | | | | | | V i d e o || | | .
. | | +---------+ | | | | | | E n c o d i n g s || | | .
. | | | | | | | | Encoding 1 || | | .
. | | View 1 | | | | | | || | | .
. | | (list of MCs) | | |-+ | +-------------------+| | | .
. | +----|-|--|------+ |-+ | | | | .
. +---------|-|--|---------+ | +-------------------+| | | .
. | | | | | A u d i o || | | .
. | | | | | E n c o d i n g s || | | .
. v | | | | Encoding 1 || | | .
. +---------|--|--------+ | | || | | .
. | Media Capture N |------>| +-------------------+| | | .
. +-+---------v--|------+ | | | | | .
. | Media Capture 2 | | | | |-+ .
. +-+--------------v----+ |-------->| | | .
. | Media Capture 1 | | | | |-+ .
. | +----------------+ |---------->| | .
. | | Attributes | | |_+ +----------------------+ .
. | +----------------+ |_+ .
. +---------------------+ .
. .
...................................................................
Figure 1: Advertisement Structure
A very brief outline of the call flow used by a simple system (two
Endpoints) in compliance with this document can be described as
follows, and as shown in the following figure.
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+-----------+ +-----------+
| Endpoint1 | | Endpoint2 |
+----+------+ +-----+-----+
| INVITE (BASIC SDP+CLUECHANNEL) |
|--------------------------------->|
| 200 0K (BASIC SDP+CLUECHANNEL)|
|<---------------------------------|
| ACK |
|--------------------------------->|
| |
|<################################>|
| BASIC SDP MEDIA SESSION |
|<################################>|
| |
| CONNECT (CLUE CTRL CHANNEL) |
|=================================>|
| ... |
|<================================>|
| CLUE CTRL CHANNEL ESTABLISHED |
|<================================>|
| |
| ADVERTISEMENT 1 |
|*********************************>|
| ADVERTISEMENT 2 |
|<*********************************|
| |
| CONFIGURE 1 |
|<*********************************|
| CONFIGURE 2 |
|*********************************>|
| |
| REINVITE (UPDATED SDP) |
|--------------------------------->|
| 200 0K (UPDATED SDP)|
|<---------------------------------|
| ACK |
|--------------------------------->|
| |
|<################################>|
| UPDATED SDP MEDIA SESSION |
|<################################>|
| |
v v
Figure 2: Basic Information Flow
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An initial offer/answer exchange establishes a basic media session,
for example audio-only, and a CLUE channel between two Endpoints.
With the establishment of that channel, the endpoints have
consented to use the CLUE protocol mechanisms and, therefore, MUST
adhere to the CLUE protocol suite as outlined herein.
Over this CLUE channel, the Provider in each Endpoint conveys its
characteristics and capabilities by sending an Advertisement as
specified herein. The Advertisement is typically not sufficient to
set up all media. The Consumer in the Endpoint receives the
information provided by the Provider, and can use it for two
purposes. First, it MUST construct and send a CLUE Configure
message to tell the Provider what the Consumer wishes to receive.
Second, it MAY, but is not necessarily REQUIRED to, use the
information provided to tailor the SDP it is going to send during
the following SIP offer/answer exchange, and its reaction to SDP it
receives in that step. It is often a sensible implementation
choice to do so, as the representation of the media information
conveyed over the CLUE channel can dramatically cut down on the
size of SDP messages used in the O/A exchange that follows.
Spatial relationships associated with the Media can be included in
the Advertisement, and it is often sensible for the Media Consumer
to take those spatial relationships into account when tailoring the
SDP.
This CLUE exchange MUST be followed by an SDP offer answer exchange
that not only establishes those aspects of the media that have not
been "negotiated" over CLUE, but has also the side effect of
setting up the media transmission itself, involving potentially
security exchanges, ICE, and whatnot. This step is plain vanilla
SIP, with the exception that the SDP used herein, in most (but not
necessarily all) cases can be considerably smaller than the SDP a
system would typically need to exchange if there were no pre-
established knowledge about the Provider and Consumer
characteristics. (The need for cutting down SDP size is not quite
obvious for a point-to-point call involving simple endpoints;
however, when considering a large multipoint conference involving
many multi-screen/multi-camera endpoints, each of which can operate
using multiple codecs for each camera and microphone, it becomes
perhaps somewhat more intuitive.)
During the lifetime of a call, further exchanges MAY occur over the
CLUE channel. In some cases, those further exchanges lead to a
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modified system behavior of Provider or Consumer (or both) without
any other protocol activity such as further offer/answer exchanges.
For example, voice-activated screen switching, signaled over the
CLUE channel, ought not to lead to heavy-handed mechanisms like SIP
re-invites. However, in other cases, after the CLUE negotiation an
additional offer/answer exchange becomes necessary. For example,
if both sides decide to upgrade the call from a single screen to a
multi-screen call and more bandwidth is required for the additional
video channels compared to what was previously negotiated using
offer/answer, a new O/A exchange is REQUIRED.
One aspect of the protocol outlined herein and specified in more
detail in companion documents is that it makes available
information regarding the Provider's capabilities to deliver Media,
and attributes related to that Media such as their spatial
relationship, to the Consumer. The operation of the renderer
inside the Consumer is unspecified in that it can choose to ignore
some information provided by the Provider, and/or not render media
streams available from the Provider (although it MUST follow the
CLUE protocol and, therefore, MUST gracefully receive and respond
(through a Configure) to the Provider's information). All CLUE
protocol mechanisms are OPTIONAL in the Consumer in the sense that,
while the Consumer MUST be able to receive (and, potentially,
gracefully acknowledge) CLUE messages, it is free to ignore the
information provided therein.
A CLUE-implementing device interoperates with a device that does
not support CLUE, because the non-CLUE device does, by definition,
not understand the offer of a CLUE channel in the initial
offer/answer exchange and, therefore, will reject it. This
rejection MUST be used as the indication to the CLUE-implementing
device that the other side of the communication is not compliant
with CLUE, and to fall back to behavior that does not require CLUE.
As for the media, Provider and Consumer have an end-to-end
communication relationship with respect to (RTP transported) media;
and the mechanisms described herein and in companion documents do
not change the aspects of setting up those RTP flows and sessions.
In other words, the RTP media sessions conform to the negotiated
SDP whether or not CLUE is used.
6. Spatial Relationships
In order for a Consumer to perform a proper rendering, it is often
necessary or at least helpful for the Consumer to have received
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spatial information about the streams it is receiving. CLUE
defines a coordinate system that allows Media Providers to describe
the spatial relationships of their Media Captures to enable proper
scaling and spatially sensible rendering of their streams. The
coordinate system is based on a few principles:
o Simple systems which do not have multiple Media Captures to
associate spatially need not use the coordinate model.
o Coordinates can be either in real, physical units (millimeters),
have an unknown scale or have no physical scale. Systems which
know their physical dimensions (for example professionally
installed Telepresence room systems) MUST always provide those
real-world measurements. Systems which don't know specific
physical dimensions but still know relative distances MUST use
'unknown scale'. 'No scale' is intended to be used where Media
Captures from different devices (with potentially different
scales) will be forwarded alongside one another (e.g. in the
case of an MCU).
* "Millimeters" means the scale is in millimeters.
* "Unknown" means the scale is not necessarily millimeters, but
the scale is the same for every Capture in the Capture Scene.
* "No Scale" means the scale could be different for each
capture- an MCU Provider that advertises two adjacent
captures and picks sources (which can change quickly) from
different endpoints might use this value; the scale could be
different and changing for each capture. But the areas of
capture still represent a spatial relation between captures.
o The coordinate system is right-handed Cartesian X, Y, Z with the
origin at a spatial location of the Provider's choosing. The
Provider MUST use the same coordinate system with the same scale
and origin for all coordinates within the same Capture Scene.
The direction of increasing coordinate values is:
X increases from left to right, from the point of view of an
observer at the front of the room looking toward the back
Y increases from the front of the room to the back of the room
Z increases from low to high (i.e. floor to ceiling)
Cameras in a scene typically point in the direction of increasing
Y, from front to back. But there could be multiple cameras
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pointing in different directions. If the physical space does not
have a well-defined front and back, the provider chooses any
direction for X and Y consistent with right-handed coordinates.
7. Media Captures and Capture Scenes
This section describes how Providers can describe the content of
media to Consumers.
7.1. Media Captures
Media Captures are the fundamental representations of streams that
a device can transmit. What a Media Capture actually represents is
flexible:
o It can represent the immediate output of a physical source (e.g.
camera, microphone) or 'synthetic' source (e.g. laptop computer,
DVD player).
o It can represent the output of an audio mixer or video composer
o It can represent a concept such as 'the loudest speaker'
o It can represent a conceptual position such as 'the leftmost
stream'
To identify and distinguish between multiple Capture instances
Captures have a unique identity. For instance: VC1, VC2 and AC1,
AC2, where VC1 and VC2 refer to two different video captures and
AC1 and AC2 refer to two different audio captures.
Some key points about Media Captures:
. A Media Capture is of a single media type (e.g. audio or
video)
. A Media Capture is defined in a Capture Scene and is given an
advertisement unique identity. The identity may be referenced
outside the Capture Scene that defines it through a Multiple
Content Capture (MCC)
. A Media Capture may be associated with one or more Capture
Scene Views
. A Media Capture has exactly one set of spatial information
. A Media Capture can be the source of at most one Capture
Encoding
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Each Media Capture can be associated with attributes to describe
what it represents.
7.1.1. Media Capture Attributes
Media Capture Attributes describe information about the Captures.
A Provider can use the Media Capture Attributes to describe the
Captures for the benefit of the Consumer of the Advertisement
message. Media Capture Attributes include:
. Spatial information, such as point of capture, point on line
of capture, and area of capture, all of which, in combination
define the capture field of, for example, a camera
. Other descriptive information to help the Consumer choose
between captures (description, presentation, view, priority,
language, person information and type)
. Control information for use inside the CLUE protocol suite
The sub-sections below define the Capture attributes.
7.1.1.1. Point of Capture
The Point of Capture attribute is a field with a single Cartesian
(X, Y, Z) point value which describes the spatial location of the
capturing device (such as camera). For an Audio Capture with
multiple microphones, the Point of Capture defines the nominal mid-
point of the microphones.
7.1.1.2. Point on Line of Capture
The Point on Line of Capture attribute is a field with a single
Cartesian (X, Y, Z) point value which describes a position in space
of a second point on the axis of the capturing device, toward the
direction it is pointing; the first point being the Point of
Capture (see above).
Together, the Point of Capture and Point on Line of Capture define
the direction and axis of the capturing device, for example the
optical axis of a camera or the axis of a microphone. The Media
Consumer can use this information to adjust how it renders the
received media if it so chooses.
For an Audio Capture, the Media Consumer can use this information
along with the Audio Capture Sensitivity Pattern to define a 3-
dimensional volume of capture where sounds can be expected to be
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picked up by the microphone providing this specific audio capture.
If the Consumer wants to associate an Audio Capture with a Video
Capture, it can compare this volume with the area of capture for
video media to provide a check on whether the audio capture is
indeed spatially associated with the video capture. For example, a
video area of capture that fails to intersect at all with the audio
volume of capture, or is at such a long radial distance from the
microphone point of capture that the audio level would be very low,
would be inappropriate.
7.1.1.3. Area of Capture
The Area of Capture is a field with a set of four (X, Y, Z) points
as a value which describes the spatial location of what is being
"captured". This attribute applies only to video captures, not
other types of media. By comparing the Area of Capture for
different Video Captures within the same Capture Scene a Consumer
can determine the spatial relationships between them and render
them correctly.
The four points MUST be co-planar, forming a quadrilateral, which
defines the Plane of Interest for the particular media capture.
If the Area of Capture is not specified, it means the Video Capture
is not spatially related to any other Video Capture.
For a switched capture that switches between different sections
within a larger area, the area of capture MUST use coordinates for
the larger potential area.
7.1.1.4. Mobility of Capture
The Mobility of Capture attribute indicates whether or not the
point of capture, line on point of capture, and area of capture
values stay the same over time, or are expected to change
(potentially frequently). Possible values are static, dynamic, and
highly dynamic.
An example for "dynamic" is a camera mounted on a stand which is
occasionally hand-carried and placed at different positions in
order to provide the best angle to capture a work task. A camera
worn by a person who moves around the room is an example for
"highly dynamic". In either case, the effect is that the capture
point, capture axis and area of capture change with time.
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The capture point of a static capture MUST NOT move for the life of
the conference. The capture point of dynamic captures is
categorized by a change in position followed by a reasonable period
of stability--in the order of magnitude of minutes. High dynamic
captures are categorized by a capture point that is constantly
moving. If the "area of capture", "capture point" and "line of
capture" attributes are included with dynamic or highly dynamic
captures they indicate spatial information at the time of the
Advertisement.
7.1.1.5. Audio Capture Sensitivity Pattern
The Audio Capture Sensitivity Pattern attribute applies only to
audio captures. This is an optional attribute. This attribute
gives information about the nominal sensitivity pattern of the
microphone which is the source of the capture. Possible values
include patterns such as omni, shotgun, cardioid, hyper-cardioid.
7.1.1.6. Description
The Description attribute is a human-readable description (which
could be in multiple languages) of the Capture.
7.1.1.7. Presentation
The Presentation attribute indicates that the capture originates
from a presentation device, that is one that provides supplementary
information to a conference through slides, video, still images,
data etc. Where more information is known about the capture it MAY
be expanded hierarchically to indicate the different types of
presentation media, e.g. presentation.slides, presentation.image
etc.
Note: It is expected that a number of keywords will be defined that
provide more detail on the type of presentation.
7.1.1.8. View
The View attribute is a field with enumerated values, indicating
what type of view the Capture relates to. The Consumer can use
this information to help choose which Media Captures it wishes to
receive. The value MUST be one of:
Room - Captures the entire scene
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Table - Captures the conference table with seated people
Individual - Captures an individual person
Lectern - Captures the region of the lectern including the
presenter, for example in a classroom style conference room
Audience - Captures a region showing the audience in a classroom
style conference room
7.1.1.9. Language
The language attribute indicates one or more languages used in the
content of the Media Capture. Captures MAY be offered in different
languages in case of multilingual and/or accessible conferences. A
Consumer can use this attribute to differentiate between them and
pick the appropriate one.
Note that the Language attribute is defined and meaningful both for
audio and video captures. In case of audio captures, the meaning
is obvious. For a video capture, "Language" could, for example, be
sign interpretation or text.
7.1.1.10. Person Information
The person information attribute allows a Provider to provide
specific information regarding the people in a Capture (regardless
of whether or not the capture has a Presentation attribute). The
Provider may gather the information automatically or manually from
a variety of sources however the xCard [RFC6351] format is used to
convey the information. This allows various information such as
Identification information (section 6.2/[RFC6350]), Communication
Information (section 6.4/[RFC6350]) and Organizational information
(section 6.6/[RFC6350]) to be communicated. A Consumer may then
automatically (i.e. via a policy) or manually select Captures
based on information about who is in a Capture. It also allows a
Consumer to render information regarding the people participating
in the conference or to use it for further processing.
The Provider may supply a minimal set of information or a larger
set of information. However it MUST be compliant to [RFC6350] and
supply a "VERSION" and "FN" property. A Provider may supply
multiple xCards per Capture of any KIND (section 6.1.4/[RFC6350]).
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In order to keep CLUE messages compact the Provider SHOULD use a
URI to point to any LOGO, PHOTO or SOUND contained in the xCARD
rather than transmitting the LOGO, PHOTO or SOUND data in a CLUE
message.
7.1.1.11. Person Type
The person type attribute indicates the type of people contained in
the capture in the conference with respect to the meeting agenda
(regardless of whether or not the capture has a Presentation
attribute). As a capture may include multiple people the attribute
may contain multiple values. However values shall not be repeated
within the attribute.
An Advertiser associates the person type with an individual capture
when it knows that a particular type is in the capture. If an
Advertiser cannot link a particular type with some certainty to a
capture then it is not included. A Consumer on reception of a
capture with a person type attribute knows with some certainly that
the capture contains that person type. The capture may contain
other person types but the Advertiser has not been able to
determine that this is the case.
The types of Captured people include:
. Chairman - the person responsible for running the conference
according to the agenda.
. Vice-Chairman - the person responsible for assisting the
chairman in running the meeting.
. Minute Taker - the person responsible for recording the
minutes of the conference
. Member - the person has no particular responsibilities with
respect to running the meeting.
. Presenter - the person is scheduled on the agenda to make a
presentation in the meeting. Note: This is not related to any
"active speaker" functionality.
. Translator - the person is providing some form of translation
or commentary in the meeting.
. Timekeeper - the person is responsible for maintaining the
meeting schedule.
Furthermore the person type attribute may contain one or more
strings allowing the Provider to indicate custom meeting specific
roles.
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7.1.1.12. Priority
The priority attribute indicates a relative priority between
different Media Captures. The Provider sets this priority, and the
Consumer MAY use the priority to help decide which captures it
wishes to receive.
The "priority" attribute is an integer which indicates a relative
priority between Captures. For example it is possible to assign a
priority between two presentation Captures that would allow a
remote endpoint to determine which presentation is more important.
Priority is assigned at the individual capture level. It represents
the Provider's view of the relative priority between Captures with
a priority. The same priority number MAY be used across multiple
Captures. It indicates they are equally important. If no priority
is assigned no assumptions regarding relative important of the
Capture can be assumed.
7.1.1.13. Embedded Text
The Embedded Text attribute indicates that a Capture provides
embedded textual information. For example the video Capture MAY
contain speech to text information composed with the video image.
This attribute is only applicable to video Captures and
presentation streams with visual information.
7.1.1.14. Related To
The Related To attribute indicates the Capture contains additional
complementary information related to another Capture. The value
indicates the identity of the other Capture to which this Capture
is providing additional information.
For example, a conference can utilize translators or facilitators
that provide an additional audio stream (i.e. a translation or
description or commentary of the conference). Where multiple
captures are available, it may be advantageous for a Consumer to
select a complementary Capture instead of or in addition to a
Capture it relates to.
7.2. Multiple Content Capture
The MCC indicates that one or more Single Media Captures are
contained in one Media Capture. Only one Capture type (i.e. audio,
video, etc.) is allowed in each MCC instance. The MCC may contain
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a reference to the Single Media Captures (which may have their own
attributes) as well as attributes associated with the MCC itself.
A MCC may also contain other MCCs. The MCC MAY reference Captures
from within the Capture Scene that defines it or from other Capture
Scenes. No ordering is implied by the order that Captures appear
within a MCC. A MCC MAY contain no references to other Captures to
indicate that the MCC contains content from multiple sources but no
information regarding those sources is given.
One or more MCCs may also be specified in a CSV. This allows an
Advertiser to indicate that several MCC captures are used to
represent a capture scene. Table 14 provides an example of this
case.
As outlined in section 7.1. each instance of the MCC has its own
Capture identity i.e. MCC1. It allows all the individual captures
contained in the MCC to be referenced by a single MCC identity.
The example below shows the use of a Multiple Content Capture:
+-----------------------+---------------------------------+
| Capture Scene #1 | |
+-----------------------|---------------------------------+
| VC1 | {attributes} |
| VC2 | {attributes} |
| VCn | {attributes} |
| MCC1(VC1,VC2,...VCn) | {attributes} |
| CSV(MCC1) | |
+---------------------------------------------------------+
Table 1: Multiple Content Capture concept
This indicates that MCC1 is a single capture that contains the
Captures VC1, VC2 and VC3 according to any MCC1 attributes.
7.2.1. MCC Attributes
Attributes may be associated with the MCC instance and the Single
Media Captures that the MCC references. A Provider should avoid
providing conflicting attribute values between the MCC and Single
Media Captures. Where there is conflict the attributes of the MCC
override any that may be present in the individual captures.
A Provider MAY include as much or as little of the original source
Capture information as it requires.
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There are MCC specific attributes that MUST only be used with
Multiple Content Captures. These are described in the sections
below. The attributes described in section 7.1.1. MAY also be used
with MCCs.
The spatial related attributes of an MCC indicate its area of
capture and point of capture within the scene, just like any other
media capture. The spatial information does not imply anything
about how other captures are composed within an MCC.
For example: A virtual scene could be constructed for the MCC
capture with two Video Captures with a "MaxCaptures" attribute set
to 2 and an "Area of Capture" attribute provided with an overall
area. Each of the individual Captures could then also include an
"Area of Capture" attribute with a sub-set of the overall area.
The Consumer would then know how each capture is related to others
within the scene, but not the relative position of the individual
captures within the composed capture.
+-----------------------+---------------------------------+
| Capture Scene #1 | |
+-----------------------|---------------------------------+
| VC1 | AreaofCapture=(0,0,0)(9,0,0) |
| | (0,0,9)(9,0,9) |
| VC2 | AreaofCapture=(10,0,0)(19,0,0) |
| | (10,0,9)(19,0,9) |
| MCC1(VC1,VC2) | MaxCaptures=2 |
| | AreaofCapture=(0,0,0)(19,0,0) |
| | (0,0,9)(19,0,9) |
| CSV(MCC1) | |
+---------------------------------------------------------+
Table 2: Example of MCC and Single Media Capture attributes
The sections below describe the MCC only attributes.
7.2.1.1. Maximum Number of Captures within a MCC
The Maximum Number of Captures MCC attribute indicates the maximum
number of individual captures that may appear in a Capture Encoding
at a time. The actual number at any given time can be less than
this maximum. It may be used to derive how the Single Media
Captures within the MCC are composed / switched with regards to
space and time.
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A Provider can indicate that the number of captures in a MCC
capture encoding is equal "=" to the MaxCaptures value or that
there may be any number of captures up to and including "<=" the
MaxCaptures value. This allows a Provider to distinguish between a
MCC that purely represents a composition of sources versus a MCC
that represents switched or switched and composed sources.
MaxCaptures MAY be set to one so that only content related to one
of the sources are shown in the MCC Capture Encoding at a time or
it may be set to any value up to the total number of Source Media
Captures in the MCC.
The bullets below describe how the setting of MaxCapture versus the
number of captures in the MCC affects how sources appear in a
capture encoding:
. When MaxCaptures is set to <= 1 and the number of captures in
the MCC is greater than 1 (or not specified) in the MCC this
is a switched case. Zero or 1 captures may be switched into
the capture encoding. Note: zero is allowed because of the
"<=".
. When MaxCaptures is set to = 1 and the number of captures in
the MCC is greater than 1 (or not specified) in the MCC this
is a switched case. Only one capture source is contained in a
capture encoding at a time.
. When MaxCaptures is set to <= N (with N > 1) and the number of
captures in the MCC is greater than N (or not specified) this
is a switched and composed case. The capture encoding may
contain purely switched sources (i.e. <=2 allows for 1 source
on its own), or may contain composed and switched sources
(i.e. a composition of 2 sources switched between the
sources).
. When MaxCaptures is set to = N (with N > 1) and the number of
captures in the MCC is greater than N (or not specified) this
is a switched and composed case. The capture encoding contains
composed and switched sources (i.e. a composition of N sources
switched between the sources). It is not possible to have a
single source.
. When MaxCaptures is set to <= to the number of captures in the
MCC this is a switched and composed case. The capture encoding
may contain media switched between any number (up to the
MaxCaptures) of composed sources.
. When MaxCaptures is set to = to the number of captures in the
MCC this is a composed case. All the sources are composed into
a single capture encoding.
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If this attribute is not set then as default it is assumed that all
source content can appear concurrently in the Capture Encoding
associated with the MCC.
For example: The use of MaxCaptures equal to 1 on a MCC with three
Video Captures VC1, VC2 and VC3 would indicate that the Advertiser
in the capture encoding would switch between VC1, VC2 or VC3 as
there may be only a maximum of one capture at a time.
7.2.1.2. Policy
The Policy MCC Attribute indicates the criteria that the Provider
uses to determine when and/or where media content appears in the
Capture Encoding related to the MCC.
The attribute is in the form of a token that indicates the policy
and index representing an instance of the policy.
The tokens are:
SoundLevel - This indicates that the content of the MCC is
determined by a sound level detection algorithm. For example: the
loudest (active) speaker is contained in the MCC.
RoundRobin - This indicates that the content of the MCC is
determined by a time based algorithm. For example: the Provider
provides content from a particular source for a period of time and
then provides content from another source and so on.
An index is used to represent an instance in the policy setting. A
index of 0 represents the most current instance of the policy, i.e.
the active speaker, 1 represents the previous instance, i.e. the
previous active speaker and so on.
The following example shows a case where the Provider provides two
media streams, one showing the active speaker and a second stream
showing the previous speaker.
+-----------------------+---------------------------------+
| Capture Scene #1 | |
+-----------------------|---------------------------------+
| VC1 | |
| VC2 | |
| MCC1(VC1,VC2) | Policy=SoundLevel:0 |
| | MaxCaptures=1 |
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| MCC2(VC1,VC2) | Policy=SoundLevel:1 |
| | MaxCaptures=1 |
| CSV(MCC1,MCC2) | |
+---------------------------------------------------------+
Table 3: Example Policy MCC attribute usage
7.2.1.3. Synchronisation Identity
The Synchronisation Identity MCC attribute indicates how the
individual captures in multiple MCC captures are synchronised. To
indicate that the Capture Encodings associated with MCCs contain
captures from the same source at the same time a Provider should
set the same Synchronisation Identity on each of the concerned
MCCs. It is the Provider that determines what the source for the
Captures is, so a Provider can choose how to group together Single
Media Captures into a combined "source" for the purpose of
switching them together to keep them synchronized according to the
SynchronisationID attribute. For example when the Provider is in
an MCU it may determine that each separate CLUE Endpoint is a
remote source of media. The Synchronisation Identity may be used
across media types, i.e. to synchronize audio and video related
MCCs.
Without this attribute it is assumed that multiple MCCs may provide
content from different sources at any particular point in time.
For example:
+=======================+=================================+
| Capture Scene #1 | |
+-----------------------|---------------------------------+
| VC1 | Description=Left |
| VC2 | Description=Centre |
| VC3 | Description=Right |
| AC1 | Description=room |
| CSV(VC1,VC2,VC3) | |
| CSV(AC1) | |
+=======================+=================================+
| Capture Scene #2 | |
+-----------------------|---------------------------------+
| VC4 | Description=Left |
| VC5 | Description=Centre |
| VC6 | Description=Right |
| AC2 | Description=room |
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| CSV(VC4,VC5,VC6) | |
| CSV(AC2) | |
+=======================+=================================+
| Capture Scene #3 | |
+-----------------------|---------------------------------+
| VC7 | |
| AC3 | |
+=======================+=================================+
| Capture Scene #4 | |
+-----------------------|---------------------------------+
| VC8 | |
| AC4 | |
+=======================+=================================+
| Capture Scene #3 | |
+-----------------------|---------------------------------+
| MCC1(VC1,VC4,VC7) | SynchronisationID=1 |
| | MaxCaptures=1 |
| MCC2(VC2,VC5,VC8) | SynchronisationID=1 |
| | MaxCaptures=1 |
| MCC3(VC3,VC6) | MaxCaptures=1 |
| MCC4(AC1,AC2,AC3,AC4) | SynchronisationID=1 |
| | MaxCaptures=1 |
| CSV(MCC1,MCC2,MCC3) | |
| CSV(MCC4) | |
+=======================+=================================+
Table 4: Example Synchronisation Identity MCC attribute usage
The above Advertisement would indicate that MCC1, MCC2, MCC3 and
MCC4 make up a Capture Scene. There would be four capture
encodings (one for each MCC). Because MCC1 and MCC2 have the same
SynchronisationID, each encoding from MCC1 and MCC2 respectively
would together have content from only Capture Scene 1 or only
Capture Scene 2 or the combination of VC7 and VC8 at a particular
point in time. In this case the Provider has decided the sources
to be synchronized are Scene #1, Scene #2, and Scene #3 and #4
together. The encoding from MCC3 would not be synchronised with
MCC1 or MCC2. As MCC4 also has the same Synchronisation Identity
as MCC1 and MCC2 the content of the audio encoding will be
synchronised with the video content.
7.3. Capture Scene
In order for a Provider's individual Captures to be used
effectively by a Consumer, the Provider organizes the Captures into
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one or more Capture Scenes, with the structure and contents of
these Capture Scenes being sent from the Provider to the Consumer
in the Advertisement.
A Capture Scene is a structure representing a spatial region
containing one or more Capture Devices, each capturing media
representing a portion of the region. A Capture Scene includes one
or more Capture Scene Views (CSV), with each CSV including one or
more Media Captures of the same media type. There can also be
Media Captures that are not included in a Capture Scene View. A
Capture Scene represents, for example, the video image of a group
of people seated next to each other, along with the sound of their
voices, which could be represented by some number of VCs and ACs in
the Capture Scene Views. An MCU can also describe in Capture
Scenes what it constructs from media Streams it receives.
A Provider MAY advertise one or more Capture Scenes. What
constitutes an entire Capture Scene is up to the Provider. A
simple Provider might typically use one Capture Scene for
participant media (live video from the room cameras) and another
Capture Scene for a computer generated presentation. In more
complex systems, the use of additional Capture Scenes is also
sensible. For example, a classroom may advertise two Capture
Scenes involving live video, one including only the camera
capturing the instructor (and associated audio), the other
including camera(s) capturing students (and associated audio).
A Capture Scene MAY (and typically will) include more than one type
of media. For example, a Capture Scene can include several Capture
Scene Views for Video Captures, and several Capture Scene Views for
Audio Captures. A particular Capture MAY be included in more than
one Capture Scene View.
A Provider MAY express spatial relationships between Captures that
are included in the same Capture Scene. However, there is no
spatial relationship between Media Captures from different Capture
Scenes. In other words, Capture Scenes each use their own spatial
measurement system as outlined above in section 6.
A Provider arranges Captures in a Capture Scene to help the
Consumer choose which captures it wants to render. The Capture
Scene Views in a Capture Scene are different alternatives the
Provider is suggesting for representing the Capture Scene. Each
Capture Scene View is given an advertisement unique identity. The
order of Capture Scene Views within a Capture Scene has no
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significance. The Media Consumer can choose to receive all Media
Captures from one Capture Scene View for each media type (e.g.
audio and video), or it can pick and choose Media Captures
regardless of how the Provider arranges them in Capture Scene
Views. Different Capture Scene Views of the same media type are
not necessarily mutually exclusive alternatives. Also note that
the presence of multiple Capture Scene Views (with potentially
multiple encoding options in each view) in a given Capture Scene
does not necessarily imply that a Provider is able to serve all the
associated media simultaneously (although the construction of such
an over-rich Capture Scene is probably not sensible in many cases).
What a Provider can send simultaneously is determined through the
Simultaneous Transmission Set mechanism, described in section 8.
Captures within the same Capture Scene View MUST be of the same
media type - it is not possible to mix audio and video captures in
the same Capture Scene View, for instance. The Provider MUST be
capable of encoding and sending all Captures (that have an encoding
group) in a single Capture Scene View simultaneously. The order of
Captures within a Capture Scene View has no significance. A
Consumer can decide to receive all the Captures in a single Capture
Scene View, but a Consumer could also decide to receive just a
subset of those captures. A Consumer can also decide to receive
Captures from different Capture Scene Views, all subject to the
constraints set by Simultaneous Transmission Sets, as discussed in
section 8.
When a Provider advertises a Capture Scene with multiple CSVs, it
is essentially signaling that there are multiple representations of
the same Capture Scene available. In some cases, these multiple
views would typically be used simultaneously (for instance a "video
view" and an "audio view"). In some cases the views would
conceptually be alternatives (for instance a view consisting of
three Video Captures covering the whole room versus a view
consisting of just a single Video Capture covering only the center
of a room). In this latter example, one sensible choice for a
Consumer would be to indicate (through its Configure and possibly
through an additional offer/answer exchange) the Captures of that
Capture Scene View that most closely matched the Consumer's number
of display devices or screen layout.
The following is an example of 4 potential Capture Scene Views for
an endpoint-style Provider:
1. (VC0, VC1, VC2) - left, center and right camera Video Captures
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2. (VC3) - Video Capture associated with loudest room segment
3. (VC4) - Video Capture zoomed out view of all people in the room
4. (AC0) - main audio
The first view in this Capture Scene example is a list of Video
Captures which have a spatial relationship to each other.
Determination of the order of these captures (VC0, VC1 and VC2) for
rendering purposes is accomplished through use of their Area of
Capture attributes. The second view (VC3) and the third view (VC4)
are alternative representations of the same room's video, which
might be better suited to some Consumers' rendering capabilities.
The inclusion of the Audio Capture in the same Capture Scene
indicates that AC0 is associated with all of those Video Captures,
meaning it comes from the same spatial region. Therefore, if audio
were to be rendered at all, this audio would be the correct choice
irrespective of which Video Captures were chosen.
7.3.1. Capture Scene attributes
Capture Scene Attributes can be applied to Capture Scenes as well
as to individual media captures. Attributes specified at this
level apply to all constituent Captures. Capture Scene attributes
include
. Human-readable description of the Capture Scene, which could
be in multiple languages;
. xCard scene information
. Scale information (millimeters, unknown, no scale), as
described in Section 6.
7.3.1.1. Scene Information
The Scene information attribute provides information regarding the
Capture Scene rather than individual participants. The Provider
may gather the information automatically or manually from a
variety of sources. The scene information attribute allows a
Provider to indicate information such as: organizational or
geographic information allowing a Consumer to determine which
Capture Scenes are of interest in order to then perform Capture
selection. It also allows a Consumer to render information
regarding the Scene or to use it for further processing.
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As per 7.1.1.10. the xCard format is used to convey this
information and the Provider may supply a minimal set of
information or a larger set of information.
In order to keep CLUE messages compact the Provider SHOULD use a
URI to point to any LOGO, PHOTO or SOUND contained in the xCARD
rather than transmitting the LOGO, PHOTO or SOUND data in a CLUE
message.
7.3.2. Capture Scene View attributes
A Capture Scene can include one or more Capture Scene Views in
addition to the Capture Scene wide attributes described above.
Capture Scene View attributes apply to the Capture Scene View as a
whole, i.e. to all Captures that are part of the Capture Scene
View.
Capture Scene View attributes include:
. Human-readable description (which could be in multiple
languages) of the Capture Scene View
7.3.3. Global View List
An Advertisement can include an optional Global View list. Each
item in this list is a Global View. A Global View is a set of
references to one or more Capture Scene Views of the same media
type that are defined within scenes of the same advertisement.
Each Global View in the list is a suggestion from the Provider to
the Consumer for which CSVs provide a complete representation of
the simultaneous captures provided by the Provider, across
multiple scenes. The Provider can include multiple Global Views,
to allow a Consumer to choose sets of captures appropriate to its
capabilities or application. The choice of how to make these
suggestions in the Global View list for what represents all the
scenes for which the Provider can send media is up to the
Provider. This is very similar to how each CSV represents a
particular scene.
As an example, suppose an advertisement has three scenes, and each
scene has three CSVs, ranging from one to three video captures in
each CSV. The Provider is advertising a total of nine video
Captures across three scenes. The Provider can use the Global
View list to suggest alternatives for Consumers that can't receive
all nine video Captures as separate media streams. For
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accommodating a Consumer that wants to receive three video
Captures, a Provider might suggest a Global View containing just a
single CSV with three Captures and nothing from the other two
scenes. Or a Provider might suggest a Global View containing
three different CSVs, one from each scene, with a single video
Capture in each.
Some additional rules:
. The ordering of Global Views in the Global View list is not
important.
. The ordering of CSVs within each Global View is not
important.
. A particular CSV may be used in multiple Global Views.
. The Provider must be capable of encoding and sending all
Captures within the CSVs of a given Global View
simultaneously.
The following figure shows an example of the structure of Global
Views in a Global View List.
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........................................................
. Advertisement .
. .
. +--------------+ +-------------------------+ .
. |Scene 1 | |Global View List | .
. | | | | .
. | CSV1 (v)<----------------- Global View (csv 1) | .
. | <-------. | | .
. | | *--------- Global View (csv 1,5) | .
. | CSV2 (v) | | | | .
. | | | | | .
. | CSV3 (v)<---------*------- Global View (csv 3,5) | .
. | | | | | | .
. | CSV4 (a)<----------------- Global View (csv 4) | .
. | <-----------. | | .
. +--------------+ | | *----- Global View (csv 4,6) | .
. | | | | | .
. +--------------+ | | | +-------------------------+ .
. |Scene 2 | | | | .
. | | | | | .
. | CSV5 (v)<-------' | | .
. | <---------' | .
. | | | (v) = video .
. | CSV6 (a)<-----------' (a) = audio .
. | | .
. +--------------+ .
`......................................................'
Figure 3: Global View List Structure
8. Simultaneous Transmission Set Constraints
In many practical cases, a Provider has constraints or limitations
on its ability to send Captures simultaneously. One type of
limitation is caused by the physical limitations of capture
mechanisms; these constraints are represented by a simultaneous
transmission set. The second type of limitation reflects the
encoding resources available, such as bandwidth or video encoding
throughput (macroblocks/second). This type of constraint is
captured by encoding groups, discussed below.
Some Endpoints or MCUs can send multiple Captures simultaneously;
however sometimes there are constraints that limit which Captures
can be sent simultaneously with other Captures. A device may not
be able to be used in different ways at the same time. Provider
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Advertisements are made so that the Consumer can choose one of
several possible mutually exclusive usages of the device. This
type of constraint is expressed in a Simultaneous Transmission Set,
which lists all the Captures of a particular media type (e.g.
audio, video, text) that can be sent at the same time. There are
different Simultaneous Transmission Sets for each media type in the
Advertisement. This is easier to show in an example.
Consider the example of a room system where there are three cameras
each of which can send a separate capture covering two persons
each- VC0, VC1, VC2. The middle camera can also zoom out (using an
optical zoom lens) and show all six persons, VC3. But the middle
camera cannot be used in both modes at the same time - it has to
either show the space where two participants sit or the whole six
seats, but not both at the same time. As a result, VC1 and VC3
cannot be sent simultaneously.
Simultaneous Transmission Sets are expressed as sets of the Media
Captures that the Provider could transmit at the same time (though,
in some cases, it is not intuitive to do so). If a Multiple
Content Capture is included in a Simultaneous Transmission Set it
indicates that the Capture Encoding associated with it could be
transmitted as the same time as the other Captures within the
Simultaneous Transmission Set. It does not imply that the Single
Media Captures contained in the Multiple Content Capture could all
be transmitted at the same time.
In this example the two simultaneous sets are shown in Table 5. If
a Provider advertises one or more mutually exclusive Simultaneous
Transmission Sets, then for each media type the Consumer MUST
ensure that it chooses Media Captures that lie wholly within one of
those Simultaneous Transmission Sets.
+-------------------+
| Simultaneous Sets |
+-------------------+
| {VC0, VC1, VC2} |
| {VC0, VC3, VC2} |
+-------------------+
Table 5: Two Simultaneous Transmission Sets
A Provider OPTIONALLY can include the simultaneous sets in its
Advertisement. These simultaneous set constraints apply across all
the Capture Scenes in the Advertisement. It is a syntax
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conformance requirement that the simultaneous transmission sets
MUST allow all the media captures in any particular Capture Scene
View to be used simultaneously. Similarly, the simultaneous
transmission sets MUST reflect the simultaneity expressed by any
Global View.
For shorthand convenience, a Provider MAY describe a Simultaneous
Transmission Set in terms of Capture Scene Views and Capture
Scenes. If a Capture Scene View is included in a Simultaneous
Transmission Set, then all Media Captures in the Capture Scene View
are included in the Simultaneous Transmission Set. If a Capture
Scene is included in a Simultaneous Transmission Set, then all its
Capture Scene Views (of the corresponding media type) are included
in the Simultaneous Transmission Set. The end result reduces to a
set of Media Captures, of a particular media type, in either case.
If an Advertisement does not include Simultaneous Transmission
Sets, then the Provider MUST be able to simultaneously provide all
the captures from any one CSV of each media type from each capture
scene. Likewise, if there are no Simultaneous Transmission Sets
and there is a Global View list, then the Provider MUST be able to
simultaneously provide all the captures from any particular Global
View (of each media type) from the Global View list.
If an Advertisement includes multiple Capture Scene Views in a
Capture Scene then the Consumer MAY choose one Capture Scene View
for each media type, or MAY choose individual Captures based on the
Simultaneous Transmission Sets.
9. Encodings
Individual encodings and encoding groups are CLUE's mechanisms
allowing a Provider to signal its limitations for sending Captures,
or combinations of Captures, to a Consumer. Consumers can map the
Captures they want to receive onto the Encodings, with encoding
parameters they want. As for the relationship between the CLUE-
specified mechanisms based on Encodings and the SIP Offer-Answer
exchange, please refer to section 5.
9.1. Individual Encodings
An Individual Encoding represents a way to encode a Media Capture
to become a Capture Encoding, to be sent as an encoded media stream
from the Provider to the Consumer. An Individual Encoding has a
set of parameters characterizing how the media is encoded.
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Different media types have different parameters, and different
encoding algorithms may have different parameters. An Individual
Encoding can be assigned to at most one Capture Encoding at any
given time.
Individual Encoding parameters are represented in SDP [RFC4566],
not in CLUE messages. For example, for a video encoding using
H.26x compression technologies, this can include parameters such
as:
. Maximum bandwidth;
. Maximum picture size in pixels;
. Maxmimum number of pixels to be processed per second;
The bandwidth parameter is the only one that specifically relates
to a CLUE Advertisement, as it can be further constrained by the
maximum group bandwidth in an Encoding Group.
9.2. Encoding Group
An Encoding Group includes a set of one or more Individual
Encodings, and parameters that apply to the group as a whole. By
grouping multiple individual Encodings together, an Encoding Group
describes additional constraints on bandwidth for the group. A
single Encoding Group MAY refer to encodings for different media
types.
The Encoding Group data structure contains:
. Maximum bitrate for all encodings in the group combined;
. A list of identifiers for the Individual Encodings belonging
to the group.
When the Individual Encodings in a group are instantiated into
Capture Encodings, each Capture Encoding has a bitrate that MUST be
less than or equal to the max bitrate for the particular individual
encoding. The "maximum bitrate for all encodings in the group"
parameter gives the additional restriction that the sum of all the
individual capture encoding bitrates MUST be less than or equal to
this group value.
The following diagram illustrates one example of the structure of a
media Provider's Encoding Groups and their contents.
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,-------------------------------------------------.
| Media Provider |
| |
| ,--------------------------------------. |
| | ,--------------------------------------. |
| | | ,--------------------------------------. |
| | | | Encoding Group | |
| | | | ,-----------. | |
| | | | | | ,---------. | |
| | | | | | | | ,---------.| |
| | | | | Encoding1 | |Encoding2| |Encoding3|| |
| `.| | | | | | `---------'| |
| `.| `-----------' `---------' | |
| `--------------------------------------' |
`-------------------------------------------------'
Figure 4: Encoding Group Structure
A Provider advertises one or more Encoding Groups. Each Encoding
Group includes one or more Individual Encodings. Each Individual
Encoding can represent a different way of encoding media. For
example one Individual Encoding may be 1080p60 video, another could
be 720p30, with a third being CIF, all in, for example, H.264
format.
While a typical three codec/display system might have one Encoding
Group per "codec box" (physical codec, connected to one camera and
one screen), there are many possibilities for the number of
Encoding Groups a Provider may be able to offer and for the
encoding values in each Encoding Group.
There is no requirement for all Encodings within an Encoding Group
to be instantiated at the same time.
9.3. Associating Captures with Encoding Groups
Each Media Capture, including MCCs, MAY be associated with one or
more Encoding Groups. To be eligible for configuration, a Media
Capture MUST be associated with at least one Encoding Group, which
is used to instantiate that Capture into a Capture Encoding. When
an MCC is configured all the Media Captures referenced by the MCC
will appear in the Capture Encoding according to the attributes of
the chosen encoding of the MCC. This allows an Advertiser to
specify encoding attributes associated with the Media Captures
without the need to provide an individual Capture Encoding for each
of the inputs.
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If an Encoding Group is assigned to a Media Capture referenced by
the MCC it indicates that this Capture may also have an individual
Capture Encoding.
For example:
+--------------------+------------------------------------+
| Capture Scene #1 | |
+--------------------+------------------------------------+
| VC1 | EncodeGroupID=1 |
| VC2 | |
| MCC1(VC1,VC2) | EncodeGroupID=2 |
| CSV(VC1) | |
| CSV(MCC1) | |
+--------------------+------------------------------------+
Table 6: Example usage of Encoding with MCC and source Captures
This would indicate that VC1 may be sent as its own Capture
Encoding from EncodeGroupID=1 or that it may be sent as part of a
Capture Encoding from EncodeGroupID=2 along with VC2.
More than one Capture MAY use the same Encoding Group.
The maximum number of Capture Encodings that can result from a
particular Encoding Group constraint is equal to the number of
individual Encodings in the group. The actual number of Capture
Encodings used at any time MAY be less than this maximum. Any of
the Captures that use a particular Encoding Group can be encoded
according to any of the Individual Encodings in the group.
It is a protocol conformance requirement that the Encoding Groups
MUST allow all the Captures in a particular Capture Scene View to
be used simultaneously.
10. Consumer's Choice of Streams to Receive from the Provider
After receiving the Provider's Advertisement message (that includes
media captures and associated constraints), the Consumer composes
its reply to the Provider in the form of a Configure message. The
Consumer is free to use the information in the Advertisement as it
chooses, but there are a few obviously sensible design choices,
which are outlined below.
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If multiple Providers connect to the same Consumer (i.e. in a n
MCU-less multiparty call), it is the responsibility of the Consumer
to compose Configures for each Provider that both fulfill each
Provider's constraints as expressed in the Advertisement, as well
as its own capabilities.
In an MCU-based multiparty call, the MCU can logically terminate
the Advertisement/Configure negotiation in that it can hide the
characteristics of the receiving endpoint and rely on its own
capabilities (transcoding/transrating/...) to create Media Streams
that can be decoded at the Endpoint Consumers. The timing of an
MCU's sending of Advertisements (for its outgoing ports) and
Configures (for its incoming ports, in response to Advertisements
received there) is up to the MCU and implementation dependent.
As a general outline, a Consumer can choose, based on the
Advertisement it has received, which Captures it wishes to receive,
and which Individual Encodings it wants the Provider to use to
encode the Captures.
On receipt of an Advertisement with an MCC the Consumer treats the
MCC as per other non-MCC Captures with the following differences:
- The Consumer would understand that the MCC is a Capture that
includes the referenced individual Captures and that these
individual Captures are delivered as part of the MCC's Capture
Encoding.
- The Consumer may utilise any of the attributes associated with
the referenced individual Captures and any Capture Scene attributes
from where the individual Captures were defined to choose Captures
and for rendering decisions.
- The Consumer may or may not choose to receive all the indicated
captures. Therefore it can choose to receive a sub-set ofCaptures
indicated by the MCC.
For example if the Consumer receives:
MCC1(VC1,VC2,VC3){attributes}
A Consumer could choose all the Captures within a MCCs however if
the Consumer determines that it doesn't want VC3 it can return
MCC1(VC1,VC2). If it wants all the individual Captures then it
returns only the MCC identity (i.e. MCC1). If the MCC in the
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advertisement does not reference any individual captures, then the
Consumer cannot choose what is included in the MCC, it is up to the
Provider to decide.
A Configure Message includes a list of Capture Encodings. These
are the Capture Encodings the Consumer wishes to receive from the
Provider. Each Capture Encoding refers to one Media Capture and
one Individual Encoding. A Configure Message does not include
references to Capture Scenes or Capture Scene Views.
For each Capture the Consumer wants to receive, it configures one
of the Encodings in that Capture's Encoding Group. The Consumer
does this by telling the Provider, in its Configure Message, which
Encoding to use for each chosen Capture. Upon receipt of this
Configure from the Consumer, common knowledge is established
between Provider and Consumer regarding sensible choices for the
media streams. The setup of the actual media channels, at least in
the simplest case, is left to a following offer-answer exchange.
Optimized implementations MAY speed up the reaction to the offer-
answer exchange by reserving the resources at the time of
finalization of the CLUE handshake.
CLUE advertisements and configure messages don't necessarily
require a new SDP offer-answer for every CLUE message
exchange. But the resulting encodings sent via RTP must conform to
the most recent SDP offer-answer result.
In order to meaningfully create and send an initial Configure, the
Consumer needs to have received at least one Advertisement, and an
SDP offer defining the Individual Encodings, from the Provider.
In addition, the Consumer can send a Configure at any time during
the call. The Configure MUST be valid according to the most
recently received Advertisement. The Consumer can send a Configure
either in response to a new Advertisement from the Provider or on
its own, for example because of a local change in conditions
(people leaving the room, connectivity changes, multipoint related
considerations).
When choosing which Media Streams to receive from the Provider, and
the encoding characteristics of those Media Streams, the Consumer
advantageously takes several things into account: its local
preference, simultaneity restrictions, and encoding limits.
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10.1. Local preference
A variety of local factors influence the Consumer's choice of
Media Streams to be received from the Provider:
o if the Consumer is an Endpoint, it is likely that it would
choose, where possible, to receive video and audio Captures that
match the number of display devices and audio system it has
o if the Consumer is an MCU, it MAY choose to receive loudest
speaker streams (in order to perform its own media composition)
and avoid pre-composed video Captures
o user choice (for instance, selection of a new layout) MAY result
in a different set of Captures, or different encoding
characteristics, being required by the Consumer
10.2. Physical simultaneity restrictions
Often there are physical simultaneity constraints of the Provider
that affect the Provider's ability to simultaneously send all of
the captures the Consumer would wish to receive. For instance, an
MCU, when connected to a multi-camera room system, might prefer to
receive both individual video streams of the people present in the
room and an overall view of the room from a single camera. Some
Endpoint systems might be able to provide both of these sets of
streams simultaneously, whereas others might not (if the overall
room view were produced by changing the optical zoom level on the
center camera, for instance).
10.3. Encoding and encoding group limits
Each of the Provider's encoding groups has limits on bandwidth,
and the constituent potential encodings have limits on the
bandwidth, computational complexity, video frame rate, and
resolution that can be provided. When choosing the Captures to be
received from a Provider, a Consumer device MUST ensure that the
encoding characteristics requested for each individual Capture
fits within the capability of the encoding it is being configured
to use, as well as ensuring that the combined encoding
characteristics for Captures fit within the capabilities of their
associated encoding groups. In some cases, this could cause an
otherwise "preferred" choice of capture encodings to be passed
over in favor of different Capture Encodings--for instance, if a
set of three Captures could only be provided at a low resolution
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then a three screen device could switch to favoring a single,
higher quality, Capture Encoding.
11. Extensibility
One important characteristics of the Framework is its
extensibility. The standard for interoperability and handling
multiple streams must be future-proof. The framework itself is
inherently extensible through expanding the data model types. For
example:
o Adding more types of media, such as telemetry, can done by
defining additional types of Captures in addition to audio and
video.
o Adding new functionalities, such as 3-D, say, may require
additional attributes describing the Captures.
The infrastructure is designed to be extended rather than
requiring new infrastructure elements. Extension comes through
adding to defined types.
12. Examples - Using the Framework (Informative)
This section gives some examples, first from the point of view of
the Provider, then the Consumer, then some multipoint scenarios
12.1. Provider Behavior
This section shows some examples in more detail of how a Provider
can use the framework to represent a typical case for telepresence
rooms. First an endpoint is illustrated, then an MCU case is
shown.
12.1.1. Three screen Endpoint Provider
Consider an Endpoint with the following description:
3 cameras, 3 displays, a 6 person table
o Each camera can provide one Capture for each 1/3 section of the
table
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o A single Capture representing the active speaker can be provided
(voice activity based camera selection to a given encoder input
port implemented locally in the Endpoint)
o A single Capture representing the active speaker with the other
2 Captures shown picture in picture within the stream can be
provided (again, implemented inside the endpoint)
o A Capture showing a zoomed out view of all 6 seats in the room
can be provided
The audio and video Captures for this Endpoint can be described as
follows.
Video Captures:
o VC0- (the left camera stream), encoding group=EG0, view=table
o VC1- (the center camera stream), encoding group=EG1, view=table
o VC2- (the right camera stream), encoding group=EG2, view=table
o MCC3- (the loudest panel stream), encoding group=EG1,
view=table, MaxCaptures=1
o MCC4- (the loudest panel stream with PiPs), encoding group=EG1,
view=room, MaxCaptures=3
o VC5- (the zoomed out view of all people in the room), encoding
group=EG1, view=room
o VC6- (presentation stream), encoding group=EG1, presentation
The following diagram is a top view of the room with 3 cameras, 3
displays, and 6 seats. Each camera is capturing 2 people. The
six seats are not all in a straight line.
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,-. d
( )`--.__ +---+
`-' / `--.__ | |
,-. | `-.._ |_-+Camera 2 (VC2)
( ).' <--(AC1)-+-''`+-+
`-' |_...---'' | |
,-.c+-..__ +---+
( )| ``--..__ | |
`-' | ``+-..|_-+Camera 1 (VC1)
,-. | <--(AC2)..--'|+-+ ^
( )| __..--' | | |
`-'b|..--' +---+ |X
,-. |``---..___ | | |
( )\ ```--..._|_-+Camera 0 (VC0) |
`-' \ <--(AC0) ..-''`-+ |
,-. \ __.--'' | | <----------+
( ) |..-'' +---+ Y
`-' a (0,0,0) origin is under Camera 1
Figure 5: Room Layout Top View
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The two points labeled b and c are intended to be at the midpoint
between the seating positions, and where the fields of view of the
cameras intersect.
The plane of interest for VC0 is a vertical plane that intersects
points 'a' and 'b'.
The plane of interest for VC1 intersects points 'b' and 'c'. The
plane of interest for VC2 intersects points 'c' and 'd'.
This example uses an area scale of millimeters.
Areas of capture:
bottom left bottom right top left top right
VC0 (-2011,2850,0) (-673,3000,0) (-2011,2850,757) (-673,3000,757)
VC1 ( -673,3000,0) ( 673,3000,0) ( -673,3000,757) ( 673,3000,757)
VC2 ( 673,3000,0) (2011,2850,0) ( 673,3000,757) (2011,3000,757)
MCC3(-2011,2850,0) (2011,2850,0) (-2011,2850,757) (2011,3000,757)
MCC4(-2011,2850,0) (2011,2850,0) (-2011,2850,757) (2011,3000,757)
VC5 (-2011,2850,0) (2011,2850,0) (-2011,2850,757) (2011,3000,757)
VC6 none
Points of capture:
VC0 (-1678,0,800)
VC1 (0,0,800)
VC2 (1678,0,800)
MCC3 none
MCC4 none
VC5 (0,0,800)
VC6 none
In this example, the right edge of the VC0 area lines up with the
left edge of the VC1 area. It doesn't have to be this way. There
could be a gap or an overlap. One additional thing to note for
this example is the distance from a to b is equal to the distance
from b to c and the distance from c to d. All these distances are
1346 mm. This is the planar width of each area of capture for VC0,
VC1, and VC2.
Note the text in parentheses (e.g. "the left camera stream") is
not explicitly part of the model, it is just explanatory text for
this example, and is not included in the model with the media
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captures and attributes. Also, MCC4 doesn't say anything about
how a capture is composed, so the media consumer can't tell based
on this capture that MCC4 is composed of a "loudest panel with
PiPs".
Audio Captures:
Three ceiling microphones are located between the cameras and the
table, at the same height as the cameras. The microphones point
down at an angle toward the seating positions.
o AC0 (left), encoding group=EG3
o AC1 (right), encoding group=EG3
o AC2 (center) encoding group=EG3
o AC3 being a simple pre-mixed audio stream from the room (mono),
encoding group=EG3
o AC4 audio stream associated with the presentation video (mono)
encoding group=EG3, presentation
Point of capture: Point on Line of Capture:
AC0 (-1342,2000,800) (-1342,2925,379)
AC1 ( 1342,2000,800) ( 1342,2925,379)
AC2 ( 0,2000,800) ( 0,3000,379)
AC3 ( 0,2000,800) ( 0,3000,379)
AC4 none
The physical simultaneity information is:
Simultaneous transmission set #1 {VC0, VC1, VC2, MCC3, MCC4,
VC6}
Simultaneous transmission set #2 {VC0, VC2, VC5, VC6}
This constraint indicates it is not possible to use all the VCs at
the same time. VC5 cannot be used at the same time as VC1 or MCC3
or MCC4. Also, using every member in the set simultaneously may
not make sense - for example MCC3(loudest) and MCC4 (loudest with
PIP). (In addition, there are encoding constraints that make
choosing all of the VCs in a set impossible. VC1, MCC3, MCC4,
VC5, VC6 all use EG1 and EG1 has only 3 ENCs. This constraint
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shows up in the encoding groups, not in the simultaneous
transmission sets.)
In this example there are no restrictions on which audio captures
can be sent simultaneously.
Encoding Groups:
This example has three encoding groups associated with the video
captures. Each group can have 3 encodings, but with each
potential encoding having a progressively lower specification. In
this example, 1080p60 transmission is possible (as ENC0 has a
maxPps value compatible with that). Significantly, as up to 3
encodings are available per group, it is possible to transmit some
video captures simultaneously that are not in the same view in the
capture scene. For example VC1 and MCC3 at the same time.
encodeGroupID=EG0, maxGroupBandwidth=6000000
encodeID=ENC0, maxWidth=1920, maxHeight=1088, maxFrameRate=60,
maxPps=124416000, maxBandwidth=4000000
encodeID=ENC1, maxWidth=1280, maxHeight=720, maxFrameRate=30,
maxPps=27648000, maxBandwidth=4000000
encodeID=ENC2, maxWidth=960, maxHeight=544, maxFrameRate=30,
maxPps=15552000, maxBandwidth=4000000
encodeGroupID=EG1 maxGroupBandwidth=6000000
encodeID=ENC3, maxWidth=1920, maxHeight=1088, maxFrameRate=60,
maxPps=124416000, maxBandwidth=4000000
encodeID=ENC4, maxWidth=1280, maxHeight=720, maxFrameRate=30,
maxPps=27648000, maxBandwidth=4000000
encodeID=ENC5, maxWidth=960, maxHeight=544, maxFrameRate=30,
maxPps=15552000, maxBandwidth=4000000
encodeGroupID=EG2 maxGroupBandwidth=6000000
encodeID=ENC6, maxWidth=1920, maxHeight=1088, maxFrameRate=60,
maxPps=124416000, maxBandwidth=4000000
encodeID=ENC7, maxWidth=1280, maxHeight=720, maxFrameRate=30,
maxPps=27648000, maxBandwidth=4000000
encodeID=ENC8, maxWidth=960, maxHeight=544, maxFrameRate=30,
maxPps=15552000, maxBandwidth=4000000
Figure 6: Example Encoding Groups for Video
For audio, there are five potential encodings available, so all
five audio captures can be encoded at the same time.
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encodeGroupID=EG3, maxGroupBandwidth=320000
encodeID=ENC9, maxBandwidth=64000
encodeID=ENC10, maxBandwidth=64000
encodeID=ENC11, maxBandwidth=64000
encodeID=ENC12, maxBandwidth=64000
encodeID=ENC13, maxBandwidth=64000
Figure 7: Example Encoding Group for Audio
Capture Scenes:
The following table represents the capture scenes for this
provider. Recall that a capture scene is composed of alternative
capture scene views covering the same spatial region. Capture
Scene #1 is for the main people captures, and Capture Scene #2 is
for presentation.
Each row in the table is a separate Capture Scene View
+------------------+
| Capture Scene #1 |
+------------------+
| VC0, VC1, VC2 |
| MCC3 |
| MCC4 |
| VC5 |
| AC0, AC1, AC2 |
| AC3 |
+------------------+
+------------------+
| Capture Scene #2 |
+------------------+
| VC6 |
| AC4 |
+------------------+
Table 7: Example Capture Scene Views
Different capture scenes are unique to each other, non-
overlapping. A consumer can choose a view from each capture scene.
In this case the three captures VC0, VC1, and VC2 are one way of
representing the video from the endpoint. These three captures
should appear adjacent next to each other. Alternatively, another
way of representing the Capture Scene is with the capture MCC3,
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which automatically shows the person who is talking. Similarly
for the MCC4 and VC5 alternatives.
As in the video case, the different views of audio in Capture
Scene #1 represent the "same thing", in that one way to receive
the audio is with the 3 audio captures (AC0, AC1, AC2), and
another way is with the mixed AC3. The Media Consumer can choose
an audio CSV it is capable of receiving.
The spatial ordering is understood by the media capture attributes
Area of Capture and Point of Capture and Point on Line of Capture.
A Media Consumer would likely want to choose a capture scene view
to receive based in part on how many streams it can simultaneously
receive. A consumer that can receive three people streams would
probably prefer to receive the first view of Capture Scene #1
(VC0, VC1, VC2) and not receive the other views. A consumer that
can receive only one people stream would probably choose one of
the other views.
If the consumer can receive a presentation stream too, it would
also choose to receive the only view from Capture Scene #2 (VC6).
12.1.2. Encoding Group Example
This is an example of an encoding group to illustrate how it can
express dependencies between encodings.
encodeGroupID=EG0 maxGroupBandwidth=6000000
encodeID=VIDENC0, maxWidth=1920, maxHeight=1088,
maxFrameRate=60, maxPps=62208000, maxBandwidth=4000000
encodeID=VIDENC1, maxWidth=1920, maxHeight=1088,
maxFrameRate=60, maxPps=62208000, maxBandwidth=4000000
encodeID=AUDENC0, maxBandwidth=96000
encodeID=AUDENC1, maxBandwidth=96000
encodeID=AUDENC2, maxBandwidth=96000
Here, the encoding group is EG0. Although the encoding group is
capable of transmitting up to 6Mbit/s, no individual video
encoding can exceed 4Mbit/s.
This encoding group also allows up to 3 audio encodings, AUDENC<0-
2>. It is not required that audio and video encodings reside
within the same encoding group, but if so then the group's overall
maxBandwidth value is a limit on the sum of all audio and video
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encodings configured by the consumer. A system that does not wish
or need to combine bandwidth limitations in this way should
instead use separate encoding groups for audio and video in order
for the bandwidth limitations on audio and video to not interact.
Audio and video can be expressed in separate encoding groups, as
in this illustration.
encodeGroupID=EG0 maxGroupBandwidth=6000000
encodeID=VIDENC0, maxWidth=1920, maxHeight=1088,
maxFrameRate=60, maxPps=62208000, maxBandwidth=4000000
encodeID=VIDENC1, maxWidth=1920, maxHeight=1088,
maxFrameRate=60, maxPps=62208000, maxBandwidth=4000000
encodeGroupID=EG1 maxGroupBandwidth=500000
encodeID=AUDENC0, maxBandwidth=96000
encodeID=AUDENC1, maxBandwidth=96000
encodeID=AUDENC2, maxBandwidth=96000
12.1.3. The MCU Case
This section shows how an MCU might express its Capture Scenes,
intending to offer different choices for consumers that can handle
different numbers of streams. A single audio capture stream is
provided for all single and multi-screen configurations that can
be associated (e.g. lip-synced) with any combination of video
captures at the consumer.
+-----------------------+---------------------------------+
| Capture Scene #1 | |
+-----------------------|---------------------------------+
| VC0 | VC for a single screen consumer |
| VC1, VC2 | VCs for a two screen consumer |
| VC3, VC4, VC5 | VCs for a three screen consumer |
| VC6, VC7, VC8, VC9 | VCs for a four screen consumer |
| AC0 | AC representing all participants|
| CSV(VC0) | |
| CSV(VC1,VC2) | |
| CSV(VC3,VC4,VC5) | |
| CSV(VC6,VC7,VC8,VC9) | |
| CSV(AC0) | |
+-----------------------+---------------------------------+
Table 8: MCU main Capture Scenes
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If / when a presentation stream becomes active within the
conference the MCU might re-advertise the available media as:
+------------------+--------------------------------------+
| Capture Scene #2 | note |
+------------------+--------------------------------------+
| VC10 | video capture for presentation |
| AC1 | presentation audio to accompany VC10 |
| CSV(VC10) | |
| CSV(AC1) | |
+------------------+--------------------------------------+
Table 9: MCU presentation Capture Scene
12.2. Media Consumer Behavior
This section gives an example of how a Media Consumer might behave
when deciding how to request streams from the three screen
endpoint described in the previous section.
The receive side of a call needs to balance its requirements,
based on number of screens and speakers, its decoding capabilities
and available bandwidth, and the provider's capabilities in order
to optimally configure the provider's streams. Typically it would
want to receive and decode media from each Capture Scene
advertised by the Provider.
A sane, basic, algorithm might be for the consumer to go through
each Capture Scene View in turn and find the collection of Video
Captures that best matches the number of screens it has (this
might include consideration of screens dedicated to presentation
video display rather than "people" video) and then decide between
alternative views in the video Capture Scenes based either on
hard-coded preferences or user choice. Once this choice has been
made, the consumer would then decide how to configure the
provider's encoding groups in order to make best use of the
available network bandwidth and its own decoding capabilities.
12.2.1. One screen Media Consumer
MCC3, MCC4 and VC5 are all different views by themselves, not
grouped together in a single view, so the receiving device should
choose between one of those. The choice would come down to
whether to see the greatest number of participants simultaneously
at roughly equal precedence (VC5), a switched view of just the
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loudest region (MCC3) or a switched view with PiPs (MCC4). An
endpoint device with a small amount of knowledge of these
differences could offer a dynamic choice of these options, in-
call, to the user.
12.2.2. Two screen Media Consumer configuring the example
Mixing systems with an even number of screens, "2n", and those
with "2n+1" cameras (and vice versa) is always likely to be the
problematic case. In this instance, the behavior is likely to be
determined by whether a "2 screen" system is really a "2 decoder"
system, i.e., whether only one received stream can be displayed
per screen or whether more than 2 streams can be received and
spread across the available screen area. To enumerate 3 possible
behaviors here for the 2 screen system when it learns that the far
end is "ideally" expressed via 3 capture streams:
1. Fall back to receiving just a single stream (MCC3, MCC4 or VC5
as per the 1 screen consumer case above) and either leave one
screen blank or use it for presentation if / when a
presentation becomes active.
2. Receive 3 streams (VC0, VC1 and VC2) and display across 2
screens (either with each capture being scaled to 2/3 of a
screen and the center capture being split across 2 screens) or,
as would be necessary if there were large bezels on the
screens, with each stream being scaled to 1/2 the screen width
and height and there being a 4th "blank" panel. This 4th panel
could potentially be used for any presentation that became
active during the call.
3. Receive 3 streams, decode all 3, and use control information
indicating which was the most active to switch between showing
the left and center streams (one per screen) and the center and
right streams.
For an endpoint capable of all 3 methods of working described
above, again it might be appropriate to offer the user the choice
of display mode.
12.2.3. Three screen Media Consumer configuring the example
This is the most straightforward case - the Media Consumer would
look to identify a set of streams to receive that best matched its
available screens and so the VC0 plus VC1 plus VC2 should match
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optimally. The spatial ordering would give sufficient information
for the correct video capture to be shown on the correct screen,
and the consumer would either need to divide a single encoding
group's capability by 3 to determine what resolution and frame
rate to configure the provider with or to configure the individual
video captures' encoding groups with what makes most sense (taking
into account the receive side decode capabilities, overall call
bandwidth, the resolution of the screens plus any user preferences
such as motion vs sharpness).
12.3. Multipoint Conference utilizing Multiple Content Captures
The use of MCCs allows the MCU to construct outgoing Advertisements
describing complex and media switching and composition scenarios.
The following sections provide several examples.
Note: In the examples the identities of the CLUE elements (e.g.
Captures, Capture Scene) in the incoming Advertisements overlap.
This is because there is no co-ordination between the endpoints.
The MCU is responsible for making these unique in the outgoing
advertisement.
12.3.1. Single Media Captures and MCC in the same Advertisement
Four endpoints are involved in a Conference where CLUE is used. An
MCU acts as a middlebox between the endpoints with a CLUE channel
between each endpoint and the MCU. The MCU receives the following
Advertisements.
+-----------------------+---------------------------------+
| Capture Scene #1 | Description=AustralianConfRoom |
+-----------------------|---------------------------------+
| VC1 | Description=Audience |
| | EncodeGroupID=1 |
| CSV(VC1) | |
+---------------------------------------------------------+
Table 10: Advertisement received from Endpoint A
+-----------------------+---------------------------------+
| Capture Scene #1 | Description=ChinaConfRoom |
+-----------------------|---------------------------------+
| VC1 | Description=Speaker |
| | EncodeGroupID=1 |
| VC2 | Description=Audience |
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| | EncodeGroupID=1 |
| CSV(VC1, VC2) | |
+---------------------------------------------------------+
Table 11: Advertisement received from Endpoint B
+-----------------------+---------------------------------+
| Capture Scene #1 | Description=USAConfRoom |
+-----------------------|---------------------------------+
| VC1 | Description=Audience |
| | EncodeGroupID=1 |
| CSV(VC1) | |
+---------------------------------------------------------+
Table 12: Advertisement received from Endpoint C
Note: Endpoint B above indicates that it sends two streams.
If the MCU wanted to provide a Multiple Content Capture containing
a round robin switched view of the audience from the 3 endpoints
and the speaker it could construct the following advertisement:
Advertisement sent to Endpoint F
+=======================+=================================+
| Capture Scene #1 | Description=AustralianConfRoom |
+-----------------------|---------------------------------+
| VC1 | Description=Audience |
| CSV(VC1) | |
+=======================+=================================+
| Capture Scene #2 | Description=ChinaConfRoom |
+-----------------------|---------------------------------+
| VC2 | Description=Speaker |
| VC3 | Description=Audience |
| CSV(VC2, VC3) | |
+=======================+=================================+
| Capture Scene #3 | Description=USAConfRoom |
+-----------------------|---------------------------------+
| VC4 | Description=Audience |
| CSV(VC4) | |
+=======================+=================================+
| Capture Scene #4 | |
+-----------------------|---------------------------------+
| MCC1(VC1,VC2,VC3,VC4) | Policy=RoundRobin:1 |
| | MaxCaptures=1 |
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| | EncodingGroup=1 |
| CSV(MCC1) | |
+=======================+=================================+
Table 13: Advertisement sent to Endpoint F - One Encoding
Alternatively if the MCU wanted to provide the speaker as one media
stream and the audiences as another it could assign an encoding
group to VC2 in Capture Scene 2 and provide a CSV in Capture Scene
#4 as per the example below.
Advertisement sent to Endpoint F
+=======================+=================================+
| Capture Scene #1 | Description=AustralianConfRoom |
+-----------------------|---------------------------------+
| VC1 | Description=Audience |
| CSV(VC1) | |
+=======================+=================================+
| Capture Scene #2 | Description=ChinaConfRoom |
+-----------------------|---------------------------------+
| VC2 | Description=Speaker |
| | EncodingGroup=1 |
| VC3 | Description=Audience |
| CSV(VC2, VC3) | |
+=======================+=================================+
| Capture Scene #3 | Description=USAConfRoom |
+-----------------------|---------------------------------+
| VC4 | Description=Audience |
| CSV(VC4) | |
+=======================+=================================+
| Capture Scene #4 | |
+-----------------------|---------------------------------+
| MCC1(VC1,VC3,VC4) | Policy=RoundRobin:1 |
| | MaxCaptures=1 |
| | EncodingGroup=1 |
| MCC2(VC2) | MaxCaptures=1 |
| | EncodingGroup=1 |
| CSV2(MCC1,MCC2) | |
+=======================+=================================+
Table 14: Advertisement sent to Endpoint F - Two Encodings
Therefore a Consumer could choose whether or not to have a separate
speaker related stream and could choose which endpoints to see. If
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it wanted the second stream but not the Australian conference room
it could indicate the following captures in the Configure message:
+-----------------------+---------------------------------+
| MCC1(VC3,VC4) | Encoding |
| VC2 | Encoding |
+-----------------------|---------------------------------+
Table 15: MCU case: Consumer Response
12.3.2. Several MCCs in the same Advertisement
Multiple MCCs can be used where multiple streams are used to carry
media from multiple endpoints. For example:
A conference has three endpoints D, E and F. Each end point has
three video captures covering the left, middle and right regions of
each conference room. The MCU receives the following
advertisements from D and E.
+-----------------------+---------------------------------+
| Capture Scene #1 | Description=AustralianConfRoom |
+-----------------------|---------------------------------+
| VC1 | CaptureArea=Left |
| | EncodingGroup=1 |
| VC2 | CaptureArea=Centre |
| | EncodingGroup=1 |
| VC3 | CaptureArea=Right |
| | EncodingGroup=1 |
| CSV(VC1,VC2,VC3) | |
+---------------------------------------------------------+
Table 16: Advertisement received from Endpoint D
+-----------------------+---------------------------------+
| Capture Scene #1 | Description=ChinaConfRoom |
+-----------------------|---------------------------------+
| VC1 | CaptureArea=Left |
| | EncodingGroup=1 |
| VC2 | CaptureArea=Centre |
| | EncodingGroup=1 |
| VC3 | CaptureArea=Right |
| | EncodingGroup=1 |
| CSV(VC1,VC2,VC3) | |
+---------------------------------------------------------+
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Table 17: Advertisement received from Endpoint E
The MCU wants to offer Endpoint F three Capture Encodings. Each
Capture Encoding would contain all the Captures from either
Endpoint D or Endpoint E depending based on the active speaker.
The MCU sends the following Advertisement:
+=======================+=================================+
| Capture Scene #1 | Description=AustralianConfRoom |
+-----------------------|---------------------------------+
| VC1 | |
| VC2 | |
| VC3 | |
| CSV(VC1,VC2,VC3) | |
+=======================+=================================+
| Capture Scene #2 | Description=ChinaConfRoom |
+-----------------------|---------------------------------+
| VC4 | |
| VC5 | |
| VC6 | |
| CSV(VC4,VC5,VC6) | |
+=======================+=================================+
| Capture Scene #3 | |
+-----------------------|---------------------------------+
| MCC1(VC1,VC4) | CaptureArea=Left |
| | MaxCaptures=1 |
| | SynchronisationID=1 |
| | EncodingGroup=1 |
| MCC2(VC2,VC5) | CaptureArea=Centre |
| | MaxCaptures=1 |
| | SynchronisationID=1 |
| | EncodingGroup=1 |
| MCC3(VC3,VC6) | CaptureArea=Right |
| | MaxCaptures=1 |
| | SynchronisationID=1 |
| | EncodingGroup=1 |
| CSV(MCC1,MCC2,MCC3) | |
+=======================+=================================+
Table 17: Advertisement received from Endpoint E
12.3.3. Heterogeneous conference with switching and composition
Consider a conference between endpoints with the following
characteristics:
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Endpoint A - 4 screens, 3 cameras
Endpoint B - 3 screens, 3 cameras
Endpoint C - 3 screens, 3 cameras
Endpoint D - 3 screens, 3 cameras
Endpoint E - 1 screen, 1 camera
Endpoint F - 2 screens, 1 camera
Endpoint G - 1 screen, 1 camera
This example focuses on what the user in one of the 3-camera multi-
screen endpoints sees. Call this person User A, at Endpoint A.
There are 4 large display screens at Endpoint A. Whenever somebody
at another site is speaking, all the video captures from that
endpoint are shown on the large screens. If the talker is at a 3-
camera site, then the video from those 3 cameras fills 3 of the
screens. If the talker is at a single-camera site, then video from
that camera fills one of the screens, while the other screens show
video from other single-camera endpoints.
User A hears audio from the 4 loudest talkers.
User A can also see video from other endpoints, in addition to the
current talker, although much smaller in size. Endpoint A has 4
screens, so one of those screens shows up to 9 other Media Captures
in a tiled fashion. When video from a 3 camera endpoint appears in
the tiled area, video from all 3 cameras appears together across
the screen with correct spatial relationship among those 3 images.
+---+---+---+ +-------------+ +-------------+ +-------------+
| | | | | | | | | |
+---+---+---+ | | | | | |
| | | | | | | | | |
+---+---+---+ | | | | | |
| | | | | | | | | |
+---+---+---+ +-------------+ +-------------+ +-------------+
Figure 8: Endpoint A - 4 Screen Display
User B at Endpoint B sees a similar arrangement, except there are
only 3 screens, so the 9 other Media Captures are spread out across
the bottom of the 3 displays, in a picture-in-picture (PIP) format.
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When video from a 3 camera endpoint appears in the PIP area, video
from all 3 cameras appears together across a single screen with
correct spatial relationship.
+-------------+ +-------------+ +-------------+
| | | | | |
| | | | | |
| | | | | |
| +-+ +-+ +-+ | | +-+ +-+ +-+ | | +-+ +-+ +-+ |
| +-+ +-+ +-+ | | +-+ +-+ +-+ | | +-+ +-+ +-+ |
+-------------+ +-------------+ +-------------+
Figure 9: Endpoint B - 3 Screen Display with PiPs
When somebody at a different endpoint becomes the current talker,
then User A and User B both see the video from the new talker
appear on their large screen area, while the previous talker takes
one of the smaller tiled or PIP areas. The person who is the
current talker doesn't see themselves; they see the previous talker
in their large screen area.
One of the points of this example is that endpoints A and B each
want to receive 3 capture encodings for their large display areas,
and 9 encodings for their smaller areas. A and B are be able to
each send the same Configure message to the MCU, and each receive
the same conceptual Media Captures from the MCU. The differences
are in how they are rendered and are purely a local matter at A and
B.
The Advertisements for such a scenario are described below.
+-----------------------+---------------------------------+
| Capture Scene #1 | Description=Endpoint x |
+-----------------------|---------------------------------+
| VC1 | EncodingGroup=1 |
| VC2 | EncodingGroup=1 |
| VC3 | EncodingGroup=1 |
| AC1 | EncodingGroup=2 |
| CSV1(VC1, VC2, VC3) | |
| CSV2(AC1) | |
+---------------------------------------------------------+
Table 19: Advertisement received at the MCU from Endpoints A to D
+-----------------------+---------------------------------+
| Capture Scene #1 | Description=Endpoint y |
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+-----------------------|---------------------------------+
| VC1 | EncodingGroup=1 |
| AC1 | EncodingGroup=2 |
| CSV1(VC1) | |
| CSV2(AC1) | |
+---------------------------------------------------------+
Table 20: Advertisement received at the MCU from Endpoints E to F
Rather than considering what is displayed CLUE concentrates more
on what the MCU sends. The MCU doesn't know anything about the
number of screens an endpoint has.
As Endpoints A to D each advertise that three Captures make up a
Capture Scene, the MCU offers these in a "site" switching mode.
That is that there are three Multiple Content Captures (and
Capture Encodings) each switching between Endpoints. The MCU
switches in the applicable media into the stream based on voice
activity. Endpoint A will not see a capture from itself.
Using the MCC concept the MCU would send the following
Advertisement to endpoint A:
+=======================+=================================+
| Capture Scene #1 | Description=Endpoint B |
+-----------------------|---------------------------------+
| VC4 | Left |
| VC5 | Center |
| VC6 | Right |
| AC1 | |
| CSV(VC4,VC5,VC6) | |
| CSV(AC1) | |
+=======================+=================================+
| Capture Scene #2 | Description=Endpoint C |
+-----------------------|---------------------------------+
| VC7 | Left |
| VC8 | Center |
| VC9 | Right |
| AC2 | |
| CSV(VC7,VC8,VC9) | |
| CSV(AC2) | |
+=======================+=================================+
| Capture Scene #3 | Description=Endpoint D |
+-----------------------|---------------------------------+
| VC10 | Left |
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| VC11 | Center |
| VC12 | Right |
| AC3 | |
| CSV(VC10,VC11,VC12) | |
| CSV(AC3) | |
+=======================+=================================+
| Capture Scene #4 | Description=Endpoint E |
+-----------------------|---------------------------------+
| VC13 | |
| AC4 | |
| CSV(VC13) | |
| CSV(AC4) | |
+=======================+=================================+
| Capture Scene #5 | Description=Endpoint F |
+-----------------------|---------------------------------+
| VC14 | |
| AC5 | |
| CSV(VC14) | |
| CSV(AC5) | |
+=======================+=================================+
| Capture Scene #6 | Description=Endpoint G |
+-----------------------|---------------------------------+
| VC15 | |
| AC6 | |
| CSV(VC15) | |
| CSV(AC6) | |
+=======================+=================================+
Table 21: Advertisement sent to endpoint A - Source Part
The above part of the Advertisement presents information about the
sources to the MCC. The information is effectively the same as the
received Advertisements except that there are no Capture Encodings
associated with them and the identities have been re-numbered.
In addition to the source Capture information the MCU advertises
"site" switching of Endpoints B to G in three streams.
+=======================+=================================+
| Capture Scene #7 | Description=Output3streammix |
+-----------------------|---------------------------------+
| MCC1(VC4,VC7,VC10, | CaptureArea=Left |
| VC13) | MaxCaptures=1 |
| | SynchronisationID=1 |
| | Policy=SoundLevel:0 |
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| | EncodingGroup=1 |
| | |
| MCC2(VC5,VC8,VC11, | CaptureArea=Center |
| VC14) | MaxCaptures=1 |
| | SynchronisationID=1 |
| | Policy=SoundLevel:0 |
| | EncodingGroup=1 |
| | |
| MCC3(VC6,VC9,VC12, | CaptureArea=Right |
| VC15) | MaxCaptures=1 |
| | SynchronisationID=1 |
| | Policy=SoundLevel:0 |
| | EncodingGroup=1 |
| | |
| MCC4() (for audio) | CaptureArea=whole scene |
| | MaxCaptures=1 |
| | Policy=SoundLevel:0 |
| | EncodingGroup=2 |
| | |
| MCC5() (for audio) | CaptureArea=whole scene |
| | MaxCaptures=1 |
| | Policy=SoundLevel:1 |
| | EncodingGroup=2 |
| | |
| MCC6() (for audio) | CaptureArea=whole scene |
| | MaxCaptures=1 |
| | Policy=SoundLevel:2 |
| | EncodingGroup=2 |
| | |
| MCC7() (for audio) | CaptureArea=whole scene |
| | MaxCaptures=1 |
| | Policy=SoundLevel:3 |
| | EncodingGroup=2 |
| | |
| CSV(MCC1,MCC2,MCC3) | |
| CSV(MCC4,MCC5,MCC6, | |
| MCC7) | |
+=======================+=================================+
Table 22: Advertisement send to endpoint A - switching part
The above part describes the switched 3 main streams that relate to
site switching. MaxCaptures=1 indicates that only one Capture from
the MCC is sent at a particular time. SynchronisationID=1 indicates
that the source sending is synchronised. The provider can choose to
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group together VC13, VC14, and VC15 for the purpose of switching
according to the SynchronisationID. Therefore when the provider
switches one of them into an MCC, it can also switch the others
even though they are not part of the same Capture Scene.
All the audio for the conference is included in this Scene #7.
There isn't necessarily a one to one relation between any audio
capture and video capture in this scene. Typically a change in
loudest talker will cause the MCU to switch the audio streams more
quickly than switching video streams.
The MCU can also supply nine media streams showing the active and
previous eight speakers. It includes the following in the
Advertisement:
+=======================+=================================+
| Capture Scene #8 | Description=Output9stream |
+-----------------------|---------------------------------+
| MCC8(VC4,VC5,VC6,VC7, | MaxCaptures=1 |
| VC8,VC9,VC10,VC11, | Policy=SoundLevel:0 |
| VC12,VC13,VC14,VC15)| EncodingGroup=1 |
| | |
| MCC9(VC4,VC5,VC6,VC7, | MaxCaptures=1 |
| VC8,VC9,VC10,VC11, | Policy=SoundLevel:1 |
| VC12,VC13,VC14,VC15)| EncodingGroup=1 |
| | |
to to |
| | |
| MCC16(VC4,VC5,VC6,VC7,| MaxCaptures=1 |
| VC8,VC9,VC10,VC11, | Policy=SoundLevel:8 |
| VC12,VC13,VC14,VC15)| EncodingGroup=1 |
| | |
| CSV(MCC8,MCC9,MCC10, | |
| MCC11,MCC12,MCC13,| |
| MCC14,MCC15,MCC16)| |
+=======================+=================================+
Table 23: Advertisement sent to endpoint A - 9 switched part
The above part indicates that there are 9 capture encodings. Each
of the Capture Encodings may contain any captures from any source
site with a maximum of one Capture at a time. Which Capture is
present is determined by the policy. The MCCs in this scene do not
have any spatial attributes.
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Note: The Provider alternatively could provide each of the MCCs
above in its own Capture Scene.
If the MCU wanted to provide a composed Capture Encoding containing
all of the 9 captures it could Advertise in addition:
+=======================+=================================+
| Capture Scene #9 | Description=NineTiles |
+-----------------------|---------------------------------+
| MCC13(MCC8,MCC9,MCC10,| MaxCaptures=9 |
| MCC11,MCC12,MCC13,| EncodingGroup=1 |
| MCC14,MCC15,MCC16)| |
| | |
| CSV(MCC13) | |
+=======================+=================================+
Table 24: Advertisement sent to endpoint A - 9 composed part
As MaxCaptures is 9 it indicates that the capture encoding contains
information from 9 sources at a time.
The Advertisement to Endpoint B is identical to the above other
than the captures from Endpoint A would be added and the captures
from Endpoint B would be removed. Whether the Captures are rendered
on a four screen display or a three screen display is up to the
Consumer to determine. The Consumer wants to place video captures
from the same original source endpoint together, in the correct
spatial order, but the MCCs do not have spatial attributes. So the
Consumer needs to associate incoming media packets with the
original individual captures in the advertisement (such as VC4,
VC5, and VC6) in order to know the spatial information it needs for
correct placement on the screens. The Provider can use the RTCP
CaptureId SDES item and associated RTP header extension, as
described in [I-D.ietf-clue-rtp-mapping], to convey this
information to the Consumer.
12.3.4. Heterogeneous conference with voice activated switching
This example illustrates how multipoint "voice activated switching"
behavior can be realized, with an endpoint making its own decision
about which of its outgoing video streams is considered the "active
talker" from that endpoint. Then an MCU can decide which is the
active talker among the whole conference.
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Consider a conference between endpoints with the following
characteristics:
Endpoint A - 3 screens, 3 cameras
Endpoint B - 3 screens, 3 cameras
Endpoint C - 1 screen, 1 camera
This example focuses on what the user at endpoint C sees. The
user would like to see the video capture of the current talker,
without composing it with any other video capture. In this
example endpoint C is capable of receiving only a single video
stream. The following tables describe advertisements from A and B
to the MCU, and from the MCU to C, that can be used to accomplish
this.
+-----------------------+---------------------------------+
| Capture Scene #1 | Description=Endpoint x |
+-----------------------|---------------------------------+
| VC1 | CaptureArea=Left |
| | EncodingGroup=1 |
| VC2 | CaptureArea=Center |
| | EncodingGroup=1 |
| VC3 | CaptureArea=Right |
| | EncodingGroup=1 |
| MCC1(VC1,VC2,VC3) | MaxCaptures=1 |
| | CaptureArea=whole scene |
| | Policy=SoundLevel:0 |
| | EncodingGroup=1 |
| AC1 | CaptureArea=whole scene |
| | EncodingGroup=2 |
| CSV1(VC1, VC2, VC3) | |
| CSV2(MCC1) | |
| CSV3(AC1) | |
+---------------------------------------------------------+
Table 25: Advertisement received at the MCU from Endpoints A and B
Endpoints A and B are advertising each individual video capture,
and also a switched capture MCC1 which switches between the other
three based on who is the active talker. These endpoints do not
advertise distinct audio captures associated with each individual
video capture, so it would be impossible for the MCU (as a media
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consumer) to make its own determination of which video capture is
the active talker based just on information in the audio streams.
+-----------------------+---------------------------------+
| Capture Scene #1 | Description=conference |
+-----------------------|---------------------------------+
| MCC1() | CaptureArea=Left |
| | MaxCaptures=1 |
| | SynchronisationID=1 |
| | Policy=SoundLevel:0 |
| | EncodingGroup=1 |
| | |
| MCC2() | CaptureArea=Center |
| | MaxCaptures=1 |
| | SynchronisationID=1 |
| | Policy=SoundLevel:0 |
| | EncodingGroup=1 |
| | |
| MCC3() | CaptureArea=Right |
| | MaxCaptures=1 |
| | SynchronisationID=1 |
| | Policy=SoundLevel:0 |
| | EncodingGroup=1 |
| | |
| MCC4() | CaptureArea=whole scene |
| | MaxCaptures=1 |
| | Policy=SoundLevel:0 |
| | EncodingGroup=1 |
| | |
| MCC5() (for audio) | CaptureArea=whole scene |
| | MaxCaptures=1 |
| | Policy=SoundLevel:0 |
| | EncodingGroup=2 |
| | |
| MCC6() (for audio) | CaptureArea=whole scene |
| | MaxCaptures=1 |
| | Policy=SoundLevel:1 |
| | EncodingGroup=2 |
| CSV1(MCC1,MCC2,MCC3 | |
| CSV2(MCC4) | |
| CSV3(MCC5,MCC6) | |
+---------------------------------------------------------+
Table 26: Advertisement sent from the MCU to C
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The MCU advertises one scene, with four video MCCs. Three of them
in CSV1 give a left, center, right view of the conference, with
"site switching". MCC4 provides a single video capture
representing a view of the whole conference. The MCU intends for
MCC4 to be switched between all the other original source
captures. In this example advertisement the MCU is not giving all
the information about all the other endpoints' scenes and which of
those captures is included in the MCCs. The MCU could include all
that information if it wants to give the consumers more
information, but it is not necessary for this example scenario.
The Provider advertises MCC5 and MCC6 for audio. Both are
switched captures, with different SoundLevel policies indicating
they are the top two dominant talkers. The Provider advertises
CSV3 with both MCCs, suggesting the Consumer should use both if it
can.
Endpoint C, in its configure message to the MCU, requests to
receive MCC4 for video, and MCC5 and MCC6 for audio. In order for
the MCU to get the information it needs to construct MCC4, it has
to send configure messages to A and B asking to receive MCC1 from
each of them, along with their AC1 audio. Now the MCU can use
audio energy information from the two incoming audio streams from
A and B to determine which of those alternatives is the current
talker. Based on that, the MCU uses either MCC1 from A or MCC1
from B as the source of MCC4 to send to C.
13. Acknowledgements
Allyn Romanow and Brian Baldino were authors of early versions.
Mark Gorzynski also contributed much to the initial approach.
Many others also contributed, including Christian Groves, Jonathan
Lennox, Paul Kyzivat, Rob Hansen, Roni Even, Christer Holmberg,
Stephen Botzko, Mary Barnes, John Leslie, Paul Coverdale.
14. IANA Considerations
None.
15. Security Considerations
There are several potential attacks related to telepresence, and
specifically the protocols used by CLUE, in the case of
conferencing sessions, due to the natural involvement of multiple
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endpoints and the many, often user-invoked, capabilities provided
by the systems.
An MCU involved in a CLUE session can experience many of the same
attacks as that of a conferencing system such as that enabled by
the XCON framework [RFC 6503]. Examples of attacks include the
following: an endpoint attempting to listen to sessions in which
it is not authorized to participate, an endpoint attempting to
disconnect or mute other users, and theft of service by an
endpoint in attempting to create telepresence sessions it is not
allowed to create. Thus, it is RECOMMENDED that an MCU
implementing the protocols necessary to support CLUE, follow the
security recommendations specified in the conference control
protocol documents. In the case of CLUE, SIP is the default
conferencing protocol, thus the security considerations in RFC
4579 MUST be followed.
One primary security concern, surrounding the CLUE framework
introduced in this document, involves securing the actual
protocols and the associated authorization mechanisms. These
concerns apply to endpoint to endpoint sessions, as well as
sessions involving multiple endpoints and MCUs. Figure 2 in
section 5 provides a basic flow of information exchange for CLUE
and the protocols involved.
As described in section 5, CLUE uses SIP/SDP to establish the
session prior to exchanging any CLUE specific information. Thus
the security mechanisms recommended for SIP [RFC 3261], including
user authentication and authorization, SHOULD be followed. In
addition, the media is based on RTP and thus existing RTP security
mechanisms, such as DTLS/SRTP, MUST be supported.
A separate data channel is established to transport the CLUE
protocol messages. The contents of the CLUE protocol messages are
based on information introduced in this document, which is
represented by an XML schema for this information defined in the
CLUE data model [ref]. Some of the information which could
possibly introduce privacy concerns is the xCard information as
described in section 7.1.1.11. In addition, the (text)
description field in the Media Capture attribute (section 7.1.1.7)
could possibly reveal sensitive information or specific
identities. The same would be true for the descriptions in the
Capture Scene (section 7.3.1) and Capture Scene View (7.3.2)
attributes. One other important consideration for the
information in the xCard as well as the description field in the
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Media Capture and Capture Scene View attributes is that while the
endpoints involved in the session have been authenticated, there
is no assurance that the information in the xCard or description
fields is authentic. Thus, this information SHOULD not be used to
make any authorization decisions and the participants in the
sessions SHOULD be made aware of this.
While other information in the CLUE protocol messages does not
reveal specific identities, it can reveal characteristics and
capabilities of the endpoints. That information could possibly
uniquely identify specific endpoints. It might also be possible
for an attacker to manipulate the information and disrupt the CLUE
sessions. It would also be possible to mount a DoS attack on the
CLUE endpoints if a malicious agent has access to the data
channel. Thus, It MUST be possible for the endpoints to establish
a channel which is secure against both message recovery and
message modification. Further details on this are provided in the
CLUE data channel solution document.
There are also security issues associated with the authorization
to perform actions at the CLUE endpoints to invoke specific
capabilities (e.g., re-arranging screens, sharing content, etc.).
However, the policies and security associated with these actions
are outside the scope of this document and the overall CLUE
solution.
16. Changes Since Last Version
NOTE TO THE RFC-Editor: Please remove this section prior to
publication as an RFC.
Changes from 18 to 19:
1. Remove the Max Capture Encodings media capture attribute.
2. Refer to RTP mapping document in the MCC example section.
3. Update references to current versions of drafts in progress.
Changes from 17 to 18:
1. Add separate definition of Global View List.
2. Add diagram for Global View List structure.
3. Tweak definitions of Media Consumer and Provider.
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Changes from 16 to 17:
1. Ticket #59 - rename Capture Scene Entry (CSE) to Capture
Scene View (CSV)
2. Ticket #60 - rename Global CSE List to Global View List
3. Ticket #61 - Proposal for describing the coordinate system.
Describe it better, without conflicts if cameras point in
different directions.
4. Minor clarifications and improved wording for Synchronisation
Identity, MCC, Simultaneous Transmission Set.
5. Add definitions for CLUE-capable device and CLUE-enabled
call, taken from the signaling draft.
6. Update definitions of Capture Device, Media Consumer, Media
Provider, Endpoint, MCU, MCC.
7. Replace "middle box" with "MCU".
8. Explicitly state there can also be Media Captures that are
not included in a Capture Scene View.
9. Explicitly state "A single Encoding Group MAY refer to
encodings for different media types."
10. In example 12.1.1 add axes and audio captures to the
diagram, and describe placement of microphones.
11. Add references to data model and signaling drafts.
12. Split references into Normative and Informative sections.
Add heading number for references section.
Changes from 15 to 16:
1. Remove Audio Channel Format attribute
2. Add Audio Capture Sensitivity Pattern attribute
3. Clarify audio spatial information regarding point of capture
and point on line of capture. Area of capture does not apply
to audio.
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4. Update section 12 example for new treatment of audio spatial
information.
5. Clean up wording of some definitions, and various places in
sections 5 and 10.
6. Remove individual encoding parameter paragraph from section
9.
7. Update Advertisement diagram.
8. Update Acknowledgements.
9. References to use cases and requirements now refer to RFCs.
10. Minor editorial changes.
Changes from 14 to 15:
1. Add "=" and "<=" qualifiers to MaxCaptures attribute, and
clarify the meaning regarding switched and composed MCC.
2. Add section 7.3.3 Global Capture Scene Entry List, and a few
other sentences elsewhere that refer to global CSE sets.
3. Clarify: The Provider MUST be capable of encoding and sending
all Captures (*that have an encoding group*) in a single
Capture Scene Entry simultaneously.
4. Add voice activated switching example in section 12.
5. Change name of attributes Participant Info/Type to Person
Info/Type.
6. Clarify the Person Info/Type attributes have the same meaning
regardless of whether or not the capture has a Presentation
attribute.
7. Update example section 12.1 to be consistent with the rest of
the document, regarding MCC and capture attributes.
8. State explicitly each CSE has a unique ID.
Changes from 13 to 14:
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1. Fill in section for Security Considerations.
2. Replace Role placeholder with Participant Information,
Participant Type, and Scene Information attributes.
3. Spatial information implies nothing about how constituent
media captures are combined into a composed MCC.
4. Clean up MCC example in Section 12.3.3. Clarify behavior of
tiled and PIP display windows. Add audio. Add new open
issue about associating incoming packets to original source
capture.
5. Remove editor's note and associated statement about RTP
multiplexing at end of section 5.
6. Remove editor's note and associated paragraph about
overloading media channel with both CLUE and non-CLUE usage,
in section 5.
7. In section 10, clarify intent of media encodings conforming
to SDP, even with multiple CLUE message exchanges. Remove
associated editor's note.
Changes from 12 to 13:
1. Added the MCC concept including updates to existing sections
to incorporate the MCC concept. New MCC attributes:
MaxCaptures, SynchronisationID and Policy.
2. Removed the "composed" and "switched" Capture attributes due
to overlap with the MCC concept.
3. Removed the "Scene-switch-policy" CSE attribute, replaced by
MCC and SynchronisationID.
4. Editorial enhancements including numbering of the Capture
attribute sections, tables, figures etc.
Changes from 11 to 12:
1. Ticket #44. Remove note questioning about requiring a
Consumer to send a Configure after receiving Advertisement.
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2. Ticket #43. Remove ability for consumer to choose value of
attribute for scene-switch-policy.
3. Ticket #36. Remove computational complexity parameter,
MaxGroupPps, from Encoding Groups.
4. Reword the Abstract and parts of sections 1 and 4 (now 5)
based on Mary's suggestions as discussed on the list. Move
part of the Introduction into a new section Overview &
Motivation.
5. Add diagram of an Advertisement, in the Overview of the
Framework/Model section.
6. Change Intended Status to Standards Track.
7. Clean up RFC2119 keyword language.
Changes from 10 to 11:
1. Add description attribute to Media Capture and Capture Scene
Entry.
2. Remove contradiction and change the note about open issue
regarding always responding to Advertisement with a Configure
message.
3. Update example section, to cleanup formatting and make the
media capture attributes and encoding parameters consistent
with the rest of the document.
Changes from 09 to 10:
1. Several minor clarifications such as about SDP usage, Media
Captures, Configure message.
2. Simultaneous Set can be expressed in terms of Capture Scene
and Capture Scene Entry.
3. Removed Area of Scene attribute.
4. Add attributes from draft-groves-clue-capture-attr-01.
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5. Move some of the Media Capture attribute descriptions back
into this document, but try to leave detailed syntax to the
data model. Remove the OUTSOURCE sections, which are already
incorporated into the data model document.
Changes from 08 to 09:
1. Use "document" instead of "memo".
2. Add basic call flow sequence diagram to introduction.
3. Add definitions for Advertisement and Configure messages.
4. Add definitions for Capture and Provider.
5. Update definition of Capture Scene.
6. Update definition of Individual Encoding.
7. Shorten definition of Media Capture and add key points in the
Media Captures section.
8. Reword a bit about capture scenes in overview.
9. Reword about labeling Media Captures.
10. Remove the Consumer Capability message.
11. New example section heading for media provider behavior
12. Clarifications in the Capture Scene section.
13. Clarifications in the Simultaneous Transmission Set section.
14. Capitalize defined terms.
15. Move call flow example from introduction to overview section
16. General editorial cleanup
17. Add some editors' notes requesting input on issues
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18. Summarize some sections, and propose details be outsourced
to other documents.
Changes from 06 to 07:
1. Ticket #9. Rename Axis of Capture Point attribute to Point
on Line of Capture. Clarify the description of this
attribute.
2. Ticket #17. Add "capture encoding" definition. Use this new
term throughout document as appropriate, replacing some usage
of the terms "stream" and "encoding".
3. Ticket #18. Add Max Capture Encodings media capture
attribute.
4. Add clarification that different capture scene entries are
not necessarily mutually exclusive.
Changes from 05 to 06:
1. Capture scene description attribute is a list of text strings,
each in a different language, rather than just a single string.
2. Add new Axis of Capture Point attribute.
3. Remove appendices A.1 through A.6.
4. Clarify that the provider must use the same coordinate system
with same scale and origin for all coordinates within the same
capture scene.
Changes from 04 to 05:
1. Clarify limitations of "composed" attribute.
2. Add new section "capture scene entry attributes" and add the
attribute "scene-switch-policy".
3. Add capture scene description attribute and description
language attribute.
4. Editorial changes to examples section for consistency with the
rest of the document.
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Changes from 03 to 04:
1. Remove sentence from overview - "This constitutes a significant
change ..."
2. Clarify a consumer can choose a subset of captures from a
capture scene entry or a simultaneous set (in section "capture
scene" and "consumer's choice...").
3. Reword first paragraph of Media Capture Attributes section.
4. Clarify a stereo audio capture is different from two mono audio
captures (description of audio channel format attribute).
5. Clarify what it means when coordinate information is not
specified for area of capture, point of capture, area of scene.
6. Change the term "producer" to "provider" to be consistent (it
was just in two places).
7. Change name of "purpose" attribute to "content" and refer to
RFC4796 for values.
8. Clarify simultaneous sets are part of a provider advertisement,
and apply across all capture scenes in the advertisement.
9. Remove sentence about lip-sync between all media captures in a
capture scene.
10. Combine the concepts of "capture scene" and "capture set"
into a single concept, using the term "capture scene" to
replace the previous term "capture set", and eliminating the
original separate capture scene concept.
17. Normative References
[I-D.ietf-clue-datachannel]
Holmberg, C., "CLUE Protocol Data Channel", draft-
ietf-clue-datachannel-05 (work in progress), November
2014.
[I-D.ietf-clue-data-model-schema]
Presta, R., Romano, S P., "An XML Schema for the CLUE
data model", draft-ietf-clue-data-model-schema-07 (work
in progress), September 2014.
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[I-D.ietf-clue-protocol]
Presta, R. and S. Romano, "CLUE protocol", draft-
ietf-clue-protocol-02 (work in progress), October 2014.
[I-D.ietf-clue-signaling]
Kyzivat, P., Xiao, L., Groves, C., Hansen, R., "CLUE
Signaling", draft-ietf-clue-signaling-04 (work in
progress), October 2014.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC3261] Rosenberg, J., Schulzrinne, H., Camarillo, G.,
Johnston,
A., Peterson, J., Sparks, R., Handley, M., and E.
Schooler, "SIP: Session Initiation Protocol", RFC 3261,
June 2002.
[RFC3264] Rosenberg, J., Schulzrinne, H., "An Offer/Answer Model
with the Session Description Protocol (SDP)", RFC 3264,
June 2002.
[RFC3550] Schulzrinne, H., Casner, S., Frederick, R., and V.
Jacobson, "RTP: A Transport Protocol for Real-Time
Applications", STD 64, RFC 3550, July 2003.
[RFC4579] Johnston, A., Levin, O., "SIP Call Control -
Conferencing for User Agents", RFC 4579, August 2006
18. Informative References
[I-D.ietf-clue-rtp-mapping]
Even, R., Lennox, J., "Mapping RP streams to CLUE media
captures", draft-ietf-clue-rtp-mapping-03 (work in
progress), October 2014.
[RFC4353] Rosenberg, J., "A Framework for Conferencing with the
Session Initiation Protocol (SIP)", RFC 4353,
February 2006.
[RFC5117] Westerlund, M. and S. Wenger, "RTP Topologies", RFC
5117, January 2008.
[RFC7205] Romanow, A., Botzko, S., Duckworth, M., Even, R.,
"Use Cases for Telepresence Multistreams", RFC 7205,
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April 2014.
[RFC7262] Romanow, A., Botzko, S., Barnes, M., "Requirements
for Telepresence Multistreams", RFC 7262, June 2014.
19. Authors' Addresses
Mark Duckworth (editor)
Polycom
Andover, MA 01810
USA
Email: mark.duckworth@polycom.com
Andrew Pepperell
Acano
Uxbridge, England
UK
Email: apeppere@gmail.com
Stephan Wenger
Vidyo, Inc.
433 Hackensack Ave.
Hackensack, N.J. 07601
USA
Email: stewe@stewe.org
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