CLUE WG A. Romanow
Internet-Draft Cisco Systems
Intended status: Informational M. Duckworth, Ed.
Expires: August 7, 2012 Polycom
A. Pepperell
B. Baldino
Cisco Systems
February 4, 2012
Framework for Telepresence Multi-Streams
draft-ietf-clue-framework-03.txt
Abstract
This memo offers a framework for a protocol that enables devices in a
telepresence conference to interoperate by specifying the
relationships between multiple media streams.
Status of this Memo
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This Internet-Draft will expire on August 7, 2012.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 3
3. Definitions . . . . . . . . . . . . . . . . . . . . . . . . . 3
4. Overview of the Framework/Model . . . . . . . . . . . . . . . 6
5. Spatial Relationships . . . . . . . . . . . . . . . . . . . . 8
6. Media Captures and Capture Sets . . . . . . . . . . . . . . . 8
6.1. Media Captures . . . . . . . . . . . . . . . . . . . . . . 9
6.1.1. Media Capture Attributes . . . . . . . . . . . . . . . 9
6.2. Capture Set . . . . . . . . . . . . . . . . . . . . . . . 11
6.2.1. Capture set attributes . . . . . . . . . . . . . . . . 12
6.3. Simultaneous Transmission Set Constraints . . . . . . . . 13
7. Encodings . . . . . . . . . . . . . . . . . . . . . . . . . . 14
7.1. Individual Encodings . . . . . . . . . . . . . . . . . . . 14
7.2. Encoding Group . . . . . . . . . . . . . . . . . . . . . . 15
8. Associating Media Captures with Encoding Groups . . . . . . . 16
9. Consumer's Choice of Streams to Receive from the Provider . . 17
9.1. Local preference . . . . . . . . . . . . . . . . . . . . . 17
9.2. Physical simultaneity restrictions . . . . . . . . . . . . 18
9.3. Encoding and encoding group limits . . . . . . . . . . . . 18
9.4. Message Flow . . . . . . . . . . . . . . . . . . . . . . . 18
10. Extensibility . . . . . . . . . . . . . . . . . . . . . . . . 19
11. Examples - Using the Framework . . . . . . . . . . . . . . . . 20
11.1. Three screen endpoint media provider . . . . . . . . . . . 20
11.2. Encoding Group Example . . . . . . . . . . . . . . . . . . 26
11.3. The MCU Case . . . . . . . . . . . . . . . . . . . . . . . 27
11.4. Media Consumer Behavior . . . . . . . . . . . . . . . . . 27
11.4.1. One screen consumer . . . . . . . . . . . . . . . . . 28
11.4.2. Two screen consumer configuring the example . . . . . 28
11.4.3. Three screen consumer configuring the example . . . . 29
12. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 29
13. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 29
14. Security Considerations . . . . . . . . . . . . . . . . . . . 29
15. Informative References . . . . . . . . . . . . . . . . . . . . 29
Appendix A. Open Issues . . . . . . . . . . . . . . . . . . . . . 30
A.1. Video layout arrangements and centralized composition . . 30
A.2. Source is selectable . . . . . . . . . . . . . . . . . . . 30
A.3. Media Source Selection . . . . . . . . . . . . . . . . . . 30
A.4. Endpoint requesting many streams from MCU . . . . . . . . 31
A.5. VAD (voice activity detection) tagging of audio streams . 31
A.6. Private Information . . . . . . . . . . . . . . . . . . . 31
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 31
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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 draft provides a framework for a protocol to
enable interoperability by handling multiple streams in a
standardized way. It is intended to support the use cases described
in draft-ietf-clue-telepresence-use-cases-02 and to meet the
requirements in draft-ietf-clue-telepresence-requirements-01.
The solution described here is strongly focused on what is being done
today, rather than on a vision of future conferencing. At the same
time, the highest priority has been given to creating an extensible
framework to make it easy to accommodate future conferencing
functionality as it evolves.
The purpose of this effort is to make it possible to handle multiple
streams of media in such a way that a satisfactory user experience is
possible even when participants are using different vendor equipment,
and also when they are using devices with different types of
communication capabilities. Information about the relationship of
media streams at the provider's end must be communicated so that
streams can be chosen and audio/video rendering can be done in the
best possible manner.
There is no attempt here to dictate to the renderer what it should
do. What the renderer does is up to the renderer.
After the following Definitions, a short section introduces key
concepts. The body of the text comprises several sections about the
key elements of the framework, how a consumer chooses streams to
receive, and some examples. The appendix describe topics that are
under discussion for adding to the document.
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 definitions marked with an "*" are new; all the others are from
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draft-wenger-clue-definitions-00-01.txt.
*Audio Capture: Media Capture for audio. Denoted as ACn.
Camera-Left and Right: For media captures, camera-left and camera-
right are from the point of view of a person observing the rendered
media. They are the opposite of stage-left and stage-right.
Capture Device: A device that converts audio and video input into an
electrical signal, in most cases to be fed into a media encoder.
Cameras and microphones are examples for capture devices.
*Capture Scene: the scene that is captured by a collection of Capture
Devices. A Capture Scene may be represented by more than one type of
Media. A Capture Scene may include more than one Media Capture of
the same type. An example of a Capture Scene is 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. A middle box may also express Capture Scenes that it constructs
from Media streams it receives.
*Capture Set: A Capture Set includes media captures that are arranged
by the provider to help the consumer choose which captures it wants.
The entries in a Capture Set represent different alternatives for
representing the same Capture Scene.
Conference: used as defined in [RFC4353], A Framework for
Conferencing within the Session Initiation Protocol (SIP).
*Individual Encoding: A variable with a set of attributes that
describes the maximum values of a single audio or video capture
encoding. The attributes include: maximum bandwidth- and for video
maximum macroblocks (for H.264), maximum width, maximum height,
maximum frame rate.
*Encoding Group: A set of encoding parameters representing a media
provider's encoding capabilities. Media stream providers formed of
multiple physical units, in each of which resides some encoding
capability, would typically advertise themselves to the remote media
stream consumer using multiple encoding groups. Within each encoding
group, multiple potential encodings are possible, with the sum of the
chosen encodings' characteristics constrained to being less than or
equal to the group-wide constraints.
Endpoint: 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
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exactly one [RFC4353] Participant (which, in turn, includes exactly
one SIP User Agent). In contrast to an endpoint, an MCU may also
send and receive media streams, but it is not the initiator nor the
final terminator in the sense that Media is Captured or Rendered.
Endpoints can be anything from multiscreen/multicamera rooms to
handheld devices.
Front: the portion of the room closest to the cameras. In going
towards back you move away from the cameras.
MCU: Multipoint Control Unit (MCU) - a device that connects two or
more endpoints together into one single multimedia conference
[RFC5117]. An MCU includes an [RFC4353] Mixer. [Edt. RFC4353 is
tardy in requiring that media from the mixer be sent to EACH
participant. I think we have practical use cases where this is not
the case. But the bug (if it is one) is in 4353 and not herein.]
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. A Media Capture (MC) may be the source of one or more Media
streams. A Media Capture may also be constructed from other Media
streams. A middle box can express Media Captures that it constructs
from Media streams it receives.
*Media Consumer: an Endpoint or middle box that receives media
streams
*Media Provider: an Endpoint or middle box that sends Media streams
Model: a set of assumptions a telepresence system of a given vendor
adheres to and expects the remote telepresence system(s) also to
adhere to.
*Plane of Interest: The spatial plane containing the most relevant
subject matter.
Render: the process of generating a representation from a 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.
Spatial Relation: The arrangement in space of two objects, in
contrast to relation in time or other relationships. See also
Camera-Left and Right.
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Stage-Left and Right: For media captures, stage-left and stage-right
are the opposite of camera-left and camera-right. For the case of a
person facing (and captured by) a camera, stage-left and stage-right
are from the point of view of that person.
*Stream: RTP stream as in [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 ID of a capture or a spatial location.
Telepresence: an environment that gives non co-located users or user
groups a feeling of (co-located) presence - the feeling that a Local
user is in the same room with other Local users and the Remote
parties. The inclusion of Remote parties is achieved through
multimedia communication including at least audio and video signals
of high fidelity.
*Video Capture: Media Capture for video. Denoted as VCn.
Video composite: A single image that is formed from combining visual
elements from separate sources.
4. Overview of the Framework/Model
The CLUE framework specifies how multiple media streams are to be
handled in a telepresence conference.
The main goals include:
o Interoperability
o Extensibility
o Flexibility
Interoperability is achieved by the media provider describing the
relationships between media streams in constructs that are understood
by the consumer, who can then render the media. Extensibility is
achieved through abstractions and the generality of the model, making
it easy to add new parameters. Flexibility is achieved largely by
having the consumer choose what content and format it wants to
receive from what the provider is capable of sending. This
constitutes a significant change from previous video conferencing
systems in which transmission of content was determined primarily by
the sender.
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A transmitting endpoint or MCU describes specific aspects of the
content of the media and the formatting of the media streams it can
send (advertisement); and the receiving end responds to the provider
by specifying which content and media streams it wants to receive
(configuration). The provider then transmits the asked for content
in the specified streams.
This advertisement and configuration occurs at call initiation but
may also happen at any time throughout the conference, whenever there
is a change in what the consumer wants or the provider can send.
An endpoint or MCU typically acts 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, describes
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 that represent the same scene
into capture sets. A consumer chooses which media captures it wants
to receive according to the capture sets sent by the provider.
In addition, the provider sends the consumer a description of the
streams it can send in terms of the media attributes of the stream,
in particular, well-known audio and video parameters such as
bandwidth, frame rate, macroblocks per second.
The provider also specifies constraints on its ability to provide
media, and the consumer must take these into account in choosing the
content and streams it wants. 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 constraints, such as maximum bandwidth
and maximum macroblocks/second.
The following sections discuss these constructs and processes in
detail, followed by use cases showing how the framework specification
can be used.
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5. Spatial Relationships
In order for a consumer to perform a proper rendering, it is often
necessary to provide spatial information about the streams it is
receiving. CLUE defines a coordinate system that allows producers to
describe the spatial relationships of their Media Captures to enable
proper scaling and spatial 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 either be in real, physical units (millimeters),
have an unknown scale or have no physical scale. Systems which
know their physical dimensions should always provide those real-
world measurements. Systems which don't know specific physical
dimensions but still know relative distances should 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 a middle
box).
* "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 set.
* "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 Cartesian X, Y, Z with the origin at a
spot of the provider's choosing. The provider must use the same
origin for all coordinates within the same capture set.
The direction of increasing coordinate values is:
X increases from camera left to camera right
Y increases from front to back
Z increases from low to high
6. Media Captures and Capture Sets
This section describes how media providers can describe the content
of media to consumers.
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6.1. 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 distinguish between multiple instances, video and audio captures
are numbered such as: VC1, VC2 and AC1, AC2. VC1 and VC2 refer to
two different video captures and AC1 and AC2 refer to two different
audio captures.
Each Media Capture can be associated with attributes to describe what
it represents.
6.1.1. Media Capture Attributes
Media Capture Attributes describe static information about the
captures that can be used by the consumer to help decide which Media
Captures should be requested. Attributes are defined by a variable
and its value. The currently defined attributes and their values
are:
Purpose: {main, presentation}
A field with enumerated values which describes the role of the Media
Capture and can be applied to any media type.
A value of 'main' describes the primary content of the room (such as
participant media).
A value of 'presentation' describes the secondary content of the room
(such as media coming from a laptop).
Composed: {true, false}
A field with a Boolean value which indicates whether or not the Media
Capture is a mix (audio) or composition (video) of streams.
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This attribute is not intended to describe the layout used when
compositing video streams.
Audio Channel Format: {mono, stereo} A field with enumerated values
which describes the method of encoding used for audio.
A value of 'mono' means the Audio Capture has one channel.
A value of 'stereo' means the Audio Capture has two audio channels,
left and right.
This attribute applies only to Audio Captures.
Switched: {true, false}
A field with a Boolean value which indicates whether or not the Media
Capture represents the (dynamic) most appropriate subset of a
'whole'. What is 'most appropriate' is up to the producer and could
be the active speaker, a lecturer or a VIP.
Point of Capture: {(X, Y, Z)} A field with a single Cartesian (X, Y,
Z) point value which describes the spatial location, virtual or
physical, of the capturing device (such as camera).
When the Point of Capture attribute is specified, it must include X,
Y and Z coordinates.
Area of Capture:
{bottom left(X1, Y1, Z1), bottom right(X2, Y2, Z2), top left(X3, Y3,
Z3), top right(X4, Y4, Z4)}
A field with a set of four (X, Y, Z) points as a value which describe
the spatial location of what is being "captured". By comparing the
Area of Capture for different Media Captures within the same capture
set a consumer can determine the spatial relationships between them
and render them correctly.
The four points should be co-planar. The four points form a
quadrilateral, not necessarily a rectangle.
The quadrilateral described by the four (X, Y, Z) points defines the
plane of interest for the particular media capture.
If the area of capture attribute is specified, it must include X, Y
and Z coordinates for all four points.
For a switched capture that switches between different sections
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within a larger area, the area of capture should use coordinates for
the larger potential area.
EncodingGroup: {<encodeGroupID value>}
A field with a value equal to the encodeGroupID of the encoding group
associated with the media capture.
6.2. Capture Set
In order for a provider's individual media captures to be used
effectively by a consumer, the provider organizes the media captures
into capture sets, with the structure and contents of these sets
being sent from the provider to the consumer.
A provider may advertise multiple capture sets or just a single
capture set. A capture set can be said to correspond to a provided
"scene", and a media provider might typically use one capture set for
main participant media and another capture set for a computer
generated presentation. Capture sets will commonly include media
captures of different types, for instance, audio captures and video
captures.
A provider can express spatial relationships between media captures
that are included in the same capture set. But there is no spatial
relationship between media captures that are in different capture
sets.
A capture set is most usefully thought of as being a collection of
entries, with each entry being a list of media captures. In grouping
multiple media captures together within a capture set entry, the
provider is signaling that those captures together form a
representation of that capture set's scene. Media captures within
the same capture set entry must be of the same media type - it is not
possible to mix audio and video captures in the same capture set
entry, for instance. The provider must be capable of encoding and
sending all media captures in a single entry simultaneously.
When a provider advertises a capture set with multiple entries, it is
essentially signaling that there are multiple representations of the
same scene available. In some cases, these multiple representations
would typically be used simultaneously (for instance a "video entry"
and an "audio entry"). In some cases the entries would conceptually
be alternatives (for instance an entry consisting of 3 video captures
versus an entry consisting of just a single video capture). In this
latter example, the provider would in the simple case end up
providing to the consumer the entry containing the number of video
captures that most closely matched the media consumer's number of
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display devices.
The following is an example of 4 potential capture set entries for an
endpoint-style media provider:
1. (VC0, VC1, VC2) - left, center and right camera video captures
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 entry in this capture set example is a list of video
captures with 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 entry (VC3) and the third entry (VC4) are additional
alternatives of how to capture the same room in different ways. The
inclusion of the audio capture in the same capture set indicates that
AC0 is associated with those video captures, meaning it comes from
the same scene. The audio should be rendered in conjunction with any
rendered video captures from the same capture set (for instance, the
consumer should attempt to perform lip sync between all audio and
video captures from the same capture set).
6.2.1. Capture set attributes
Attributes can be applied to capture sets as well as to individual
media captures. Attributes specified at this level apply to all
constituent media captures.
Area of Scene attribute
The area of scene attribute for a capture set has the same format as
the area of capture attribute for a media capture. The area of scene
is for the entire scene, which is captured by the one or more media
captures in the capture set entries.
Scale attribute
An optional attribute indicating if the numbers used for area of
scene, area of capture and point of capture are in terms of
millimeters, unknown scale factor, or not any scale, as described in
Section 5. If any media captures have an area of capture attribute
or point of capture attribute, then this scale attribute must also be
defined. The possible values for this attribute are:
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"millimeters"
"unknown"
"no scale"
6.3. Simultaneous Transmission Set Constraints
The provider may have constraints or limitations on its ability to
send media captures. One type 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 - bandwidth and
macroblocks/second. This type of constraint is captured by encoding
groups, discussed below.
An endpoint or MCU 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 advertisements are
made so that the consumer will 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
media captures that can be sent at the same time. This is easier to
show in an example.
Consider the example of a room system where there are 3 cameras each
of which can send a separate capture covering 2 persons each- VC0,
VC1, VC2. The middle camera can also zoom out and show all 6
persons, VC3. But the middle camera cannot be used in both modes at
the same time - it has to either show the space where 2 participants
sit or the whole 6 seats, but not both at the same time.
Simultaneous transmission sets are expressed as sets of the MCs that
could physically be transmitted at the same time, (though it may not
make sense to do so). In this example the two simultaneous sets are
shown in Table 1. The consumer must make sure that it chooses one
and not more of the mutually exclusive sets.
+-------------------+
| Simultaneous Sets |
+-------------------+
| {VC0, VC1, VC2} |
| {VC0, VC3, VC2} |
+-------------------+
Table 1: Two Simultaneous Transmission Sets
The Simultaneous Transmission Sets MUST allow all the Media Captures
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in a particular capture set entry to be used simultaneously.
7. Encodings
We have considered how providers can describe the content of media to
consumers. We will now consider how the providers communicate
information about their abilities to send streams. We introduce two
constructs - individual encodings and encoding groups. Consumers
will then map the media captures they want onto the encodings with
encoding parameters they want. This process is then described.
7.1. Individual Encodings
An individual encoding represents a way to encode a media capture to
become an encoded media stream sent from the media provider to the
media consumer. An individual encoding has a set of parameters
characterizing how the media is encoded. Different media types have
different parameters, and different encoding algorithms may have
different parameters. An individual encoding can be used for only
one actual encoded media stream at a time.
The parameters of an individual encoding represent the maximimum
values for certain aspects of the encoding. A particular
instantiation into an encoded stream might use lower values than
these maximums.
The following tables show the variables for audio and video encoding.
+--------------+----------------------------------------------------+
| Name | Description |
+--------------+----------------------------------------------------+
| encodeID | A unique identifier for the individual encoding |
| maxBandwidth | Maximum number of bits per second |
| maxH264Mbps | Maximum number of macroblocks per second: ((width |
| | + 15) / 16) * ((height + 15) / 16) * |
| | framesPerSecond |
| maxWidth | Video resolution's maximum supported width, |
| | expressed in pixels |
| maxHeight | Video resolution's maximum supported height, |
| | expressed in pixels |
| maxFrameRate | Maximum supported frame rate |
+--------------+----------------------------------------------------+
Table 2: Individual Video Encoding Parameters
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+--------------+-----------------------------------+
| Name | Description |
+--------------+-----------------------------------+
| maxBandwidth | Maximum number of bits per second |
+--------------+-----------------------------------+
Table 3: Individual Audio Encoding Parameters
7.2. Encoding Group
An encoding group includes a set of one or more individual encodings,
plus some parameters that apply to the group as a whole. By grouping
multiple individual encodings together, an encoding group describes
additional constraints on bandwidth and other parameters for the
group. Table 4 shows the parameters and individual encoding sets
that are part of an encoding group.
+-------------------+-----------------------------------------------+
| Name | Description |
+-------------------+-----------------------------------------------+
| encodeGroupID | A unique identifier for the encoding group |
| maxGroupBandwidth | Maximum number of bits per second relating to |
| | all encodings combined |
| maxGroupH264Mbps | Maximum number of macroblocks per second |
| | relating to all video encodings combined |
| videoEncodings[] | Set of potential encodings (list of |
| | encodeIDs) |
| audioEncodings[] | Set of potential encodings (list of |
| | encodeIDs) |
+-------------------+-----------------------------------------------+
Table 4: Encoding Group
When the individual encodings in a group are instantiated into actual
encoded media streams, each stream has a bandwidth that must be less
than or equal to the maxBandwidth for the particular individual
encoding. The maxGroupBandwidth parameter gives the additional
restriction that the sum of all the individual instantiated
bandwidths must be less than or equal to the maxGroupBandwidth value.
Likewise, the sum of the macroblocks per second of each instantiated
encoding in the group must not exceed the maxGroupH264Mbps value.
The following diagram illustrates the structure of a media provider's
Encoding Groups and their contents.
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,-------------------------------------------------.
| Media Provider |
| |
| ,--------------------------------------. |
| | ,--------------------------------------. |
| | | ,--------------------------------------. |
| | | | Encoding Group | |
| | | | ,-----------. | |
| | | | | | ,---------. | |
| | | | | | | | ,---------.| |
| | | | | Encoding1 | |Encoding2| |Encoding3|| |
| `.| | | | | | `---------'| |
| `.| `-----------' `---------' | |
| `--------------------------------------' |
`-------------------------------------------------'
Figure 1: Encoding Group Structure
A media 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.
While a typical 3 codec/display system might have one encoding group
per "codec box", 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 once.
8. Associating Media Captures with Encoding Groups
Every media capture is associated with an encoding group, which is
used to instantiate that media capture into one or more encoded
streams. Each media capture has an encoding group attribute. The
value of this attribute is the encodeGroupID for the encoding group
with which it is associated. More than one media capture may use the
same encoding group.
The maximum number of streams that can result from a particular
encoding group constraint is equal to the number of individual
encodings in the group. The actual number of streams used at any
time may be less than this maximum. Any of the media captures that
use a particular encoding group can be encoded according to any of
the individual encodings in the group. If there are multiple
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individual encodings in the group, then a single media capture can be
encoded into multiple different streams at the same time, with each
stream following the constraints of a different individual encoding.
The Encoding Groups MUST allow all the media captures in a particular
capture set entry to be used simultaneously.
9. Consumer's Choice of Streams to Receive from the Provider
After receiving the provider's advertised media captures and
associated constraints, the consumer must choose which media captures
it wishes to receive, and which individual encodings from the
provider it wants to use to encode the capture. Each media capture
has an encoding group ID attribute which specifies which individual
encodings are available to be used for that media capture.
For each media capture the consumer wants to receive, it configures
one or more of the encodings in that capture's encoding group. The
consumer does this by telling the provider the resolution, frame
rate, bandwidth, etc. when asking for streams for its chosen
captures. Upon receipt of this configuration command from the
consumer, the provider generates streams for each such configured
encoding and sends those streams to the consumer.
The consumer must have received at least one capture advertisement
from the provider to be able to configure the provider's generation
of media streams.
The consumer is able to change its configuration of the provider's
encodings any number of times during the call, either in response to
a new capture advertisement from the provider or autonomously. The
consumer need not send a new configure message to the provider when
it receives a new capture advertisement from the provider unless the
contents of the new capture advertisement cause the consumer's
current configure message to become invalid.
When choosing which streams to receive from the provider, and the
encoding characteristics of those streams, the consumer needs to take
several things into account its local preference, simultaneity
restrictions, and encoding limits.
9.1. Local preference
A variety of local factors will influence the consumer's choice of
streams to be received from the provider:
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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 a middle box such as 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 media captures, or different encoding
characteristics, being required by the consumer
9.2. Physical simultaneity restrictions
There may be physical simultaneity constraints imposed by the
provider that affect the provider's ability to simultaneously send
all of the captures the consumer would wish to receive. For
instance, a middle box such as an MCU, when connected to a multi-
camera room system, might prefer to receive both individual camera
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
may not (if the overall room view were produced by changing the zoom
level on the center camera, for instance).
9.3. Encoding and encoding group limits
Each of the provider's encoding groups has limits on bandwidth and
macroblocks per second, and the constituent potential encodings have
limits on the bandwidth, macroblocks per second, video frame rate,
and resolution that can be provided. When choosing the media
captures to be received from a provider, a consumer device must
ensure that the encoding characteristics requested for each
individual media capture fits within the capability of the encoding
it is being configured to use, as well as ensuring that the combined
encoding characteristics for media captures fit within the
capabilities of their associated encoding groups. In some cases,
this could cause an otherwise "preferred" choice of streams to be
passed over in favour of different streams - for instance, if a set
of 3 media captures could only be provided at a low resolution then a
3 screen device could switch to favoring a single, higher quality,
stream.
9.4. Message Flow
The following diagram shows the basic flow of messages between a
media provider and a media consumer. The usage of the "capture
advertisement" and "configure encodings" message is described above.
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The consumer also sends its own capability message to the provider
which may contain information about its own capabilities or
restrictions.
Diagram for Message Flow
Media Consumer Media Provider
-------------- ------------
| |
|----- Consumer Capability ---------->|
| |
| |
|<---- Capture advertisement ---------|
| |
| |
|------ Configure encodings --------->|
| |
In order for a maximally-capable provider to be able to advertise a
manageable number of video captures to a consumer, there is a
potential use for the consumer, at the start of CLUE, to be able to
inform the provider of its capabilities. One example here would be
the video capture attribute set - a consumer could tell the provider
the complete set of video capture attributes it is able to understand
and so the provider would be able to reduce the capture set it
advertises to be tailored to the consumer.
TBD - the content of this message needs to be better defined. The
authors believe there is a need for this message, but have not worked
out the details yet.
10. Extensibility
One of the most important characteristics of the Framework is its
extensibility. Telepresence is a relatively new industry and while
we can foresee certain directions, we also do not know everything
about how it will develop. 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.
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o Adding new functionalities , such as 3-D, say, will require
additional attributes describing the captures.
o Adding a new codecs, such as H.265, can be accomplished by
defining new encoding variables.
The infrastructure is designed to be extended rather than requiring
new infrastructure elements. Extension comes through adding to
defined types.
Assuming the implementation is in something like XML, adding data
elements and attributes makes extensibility easy.
11. Examples - Using the Framework
This section shows some examples in more detail how to use the
framework to represent a typical case for telepresence rooms. First
an endpoint is illustrated, then an MCU case is shown.
11.1. Three screen endpoint media provider
Consider an endpoint with the following description:
o 3 cameras, 3 displays, a 6 person table
o Each video device can provide one capture for each 1/3 section of
the table
o A single capture representing the active speaker can be provided
o A single capture representing the active speaker with the other 2
captures shown picture in picture within the stream can be
provided
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 camera-left camera stream), encoding group=EG0,
purpose=main;auto-switched:no
o VC1- (the center camera stream), encoding group=EG1, purpose=main;
auto-switched:no
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o VC2- (the camera-right camera stream), encoding group=EG2,
purpose=main;auto-switched:no
o VC3- (the loudest panel stream), encoding group=EG1,
purpose=main;auto-switched:yes
o VC4- (the loudest panel stream with PiPs), encoding group=EG1,
purpose=main; composed=true; auto-switched:yes
o VC5- (the zoomed out view of all people in the room), encoding
group=EG1, purpose=main; composed=no; auto-switched:no
o VC6- (presentation stream), encoding group=EG1,
purpose=presentation;auto-switched:no
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.
,-. d
( )`--.__ +---+
`-' / `--.__ | |
,-. | `-.._ |_-+Camera 2 (VC2)
( ).' ___..-+-''`+-+
`-' |_...---'' | |
,-.c+-..__ +---+
( )| ``--..__ | |
`-' | ``+-..|_-+Camera 1 (VC1)
,-. | __..--'|+-+
( )| __..--' | |
`-'b|..--' +---+
,-. |``---..___ | |
( )\ ```--..._|_-+Camera 0 (VC0)
`-' \ _..-''`-+
,-. \ __.--'' | |
( ) |..-'' +---+
`-' a
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.
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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)
VC3 (-2011,2850,0) (2011,2850,0) (-2011,2850,757) (2011,3000,757)
VC4 (-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)
VC3 none
VC4 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 camera-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
captures and attributes.
Audio Captures:
o AC0 (camera-left), encoding group=EG3, purpose=main, channel
format=mono
o AC1 (camera-right), encoding group=EG3, purpose=main, channel
format=mono
o AC2 (center) encoding group=EG3, purpose=main, channel format=mono
o AC3 being a simple pre-mixed audio stream from the room (mono),
encoding group=EG3, purpose=main, channel format=mono
o AC4 audio stream associated with the presentation video (mono)
encoding group=EG3, purpose=presentation, channel format=mono
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Areas of capture:
bottom left bottom right top left top right
AC0 (-2011,2850,0) (-673,3000,0) (-2011,2850,757) (-673,3000,757)
AC1 ( 673,3000,0) (2011,2850,0) ( 673,3000,757) (2011,3000,757)
AC2 ( -673,3000,0) ( 673,3000,0) ( -673,3000,757) ( 673,3000,757)
AC3 (-2011,2850,0) (2011,2850,0) (-2011,2850,757) (2011,3000,757)
AC4 none
The physical simultaneity information is:
{VC0, VC1, VC2, VC3, VC4, VC6}
{VC0, VC2, VC5, VC6}
This constraint indicates it is not possible to use all the VCs at
the same time. VC5 can not be used at the same time as VC1 or VC3 or
VC4. Also, using every member in the set simultaneously may not make
sense - for example VC3(loudest) and VC4 (loudest with PIP). (In
addition, there are encoding constraints that make choosing all of
the VCs in a set impossible. VC1, VC3, VC4, VC5, VC6 all use EG1 and
EG1 has only 3 ENCs. This constraint 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 maxMbps
value compatible with that) as long as it is the only active encoding
in the group(as maxMbps for the entire encoding group is also
489600). 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 entry in the capture set. For example VC1
and VC3 at the same time.
It is also possible to transmit multiple encodings of a single video
capture. For example VC0 can be encoded using ENC0 and ENC1 at the
same time, as long as the encoding parameters satisfy the constraints
of ENC0, ENC1, and EG0, such as one at 1080p30 and one at 720p30.
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encodeGroupID=EG0, maxGroupH264Mbps=489600, maxGroupBandwidth=6000000
encodeID=ENC0, maxWidth=1920, maxHeight=1088, maxFrameRate=60,
maxH264Mbps=489600, maxBandwidth=4000000
encodeID=ENC1, maxWidth=1280, maxHeight=720, maxFrameRate=30,
maxH264Mbps=108000, maxBandwidth=4000000
encodeID=ENC2, maxWidth=960, maxHeight=544, maxFrameRate=30,
maxH264Mbps=61200, maxBandwidth=4000000
encodeGroupID=EG1 maxGroupH264Mbps=489600 maxGroupBandwidth=6000000
encodeID=ENC3, maxWidth=1920, maxHeight=1088, maxFrameRate=60,
maxH264Mbps=489600, maxBandwidth=4000000
encodeID=ENC4, maxWidth=1280, maxHeight=720, maxFrameRate=30,
maxH264Mbps=108000, maxBandwidth=4000000
encodeID=ENC5, maxWidth=960, maxHeight=544, maxFrameRate=30,
maxH264Mbps=61200, maxBandwidth=4000000
encodeGroupID=EG2 maxGroupH264Mbps=489600 maxGroupBandwidth=6000000
encodeID=ENC6, maxWidth=1920, maxHeight=1088, maxFrameRate=60,
maxH264Mbps=489600, maxBandwidth=4000000
encodeID=ENC7, maxWidth=1280, maxHeight=720, maxFrameRate=30,
maxH264Mbps=108000, maxBandwidth=4000000
encodeID=ENC8, maxWidth=960, maxHeight=544, maxFrameRate=30,
maxH264Mbps=61200, maxBandwidth=4000000
Figure 2: 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.
encodeGroupID=EG3, maxGroupH264Mbps=0, maxGroupBandwidth=320000
encodeID=ENC9, maxBandwidth=64000
encodeID=ENC10, maxBandwidth=64000
encodeID=ENC11, maxBandwidth=64000
encodeID=ENC12, maxBandwidth=64000
encodeID=ENC13, maxBandwidth=64000
Figure 3: Example Encoding Group for Audio
Capture Sets:
The following table represents the capture sets for this provider.
Recall that a capture set is composed of alternative captures
covering the same scene. Capture Set #1 is for the main people
captures, and Capture Set #2 is for presentation.
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Each row in the table is a separate entry in the capture set
+----------------+
| Capture Set #1 |
+----------------+
| VC0, VC1, VC2 |
| VC3 |
| VC4 |
| VC5 |
| AC0, AC1, AC2 |
| AC3 |
+----------------+
+----------------+
| Capture Set #2 |
+----------------+
| VC6 |
| AC4 |
+----------------+
Different capture sets are unique to each other, non-overlapping. A
consumer can choose an entry from each capture set. 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 VC3, which automatically shows the
person who is talking. Similarly for the VC4 and VC5 alternatives.
As in the video case, the different entries of audio in Capture Set
#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 capture entry
it is capable of receiving.
The spatial ordering is understood by the media capture attributes
area and point of capture.
A Media Consumer would likely want to choose a capture set entry 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 entry of Capture Set #1 (VC0,
VC1, VC2) and not receive the other entries. A consumer that can
receive only one people stream would probably choose one of the other
entries.
If the consumer can receive a presentation stream too, it would also
choose to receive the only entry from Capture Set #2 (VC6).
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11.2. Encoding Group Example
This is an example of an encoding group to illustrate how it can
express dependencies between encodings.
encodeGroupID=EG0, maxGroupH264Mbps=489600, maxGroupBandwidth=6000000
encodeID=VIDENC0, maxWidth=1920, maxHeight=1088, maxFrameRate=60,
maxH264Mbps=244800, maxBandwidth=4000000
encodeID=VIDENC1, maxWidth=1920, maxHeight=1088, maxFrameRate=60,
maxH264Mbps=244800, maxBandwidth=4000000
encodeID=AUDENC0, maxBandwidth=96000
encodeID=AUDENC1, maxBandwidth=96000
encodeID=AUDENC2, maxBandwidth=96000
Here, the encoding group is EG0. It can transmit up to two 1080p30
encodings (Mbps for 1080p = 244800), but it is capable of
transmitting a maxFrameRate of 60 frames per second (fps). To
achieve the maximum resolution (1920 x 1088) the frame rate is
limited to 30 fps. However 60 fps can be achieved at a lower
resolution if required by the consumer. 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 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, maxGroupH264Mbps=489600, maxGroupBandwidth=6000000
encodeID=VIDENC0, maxWidth=1920, maxHeight=1088, maxFrameRate=60,
maxH264Mbps=244800, maxBandwidth=4000000
encodeID=VIDENC1, maxWidth=1920, maxHeight=1088, maxFrameRate=60,
maxH264Mbps=244800, maxBandwidth=4000000
encodeGroupID=EG1, maxGroupH264Mbps=0, maxGroupBandwidth=500000
encodeID=AUDENC0, maxBandwidth=96000
encodeID=AUDENC1, maxBandwidth=96000
encodeID=AUDENC2, maxBandwidth=96000
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11.3. The MCU Case
This section shows how an MCU might express its Capture Sets,
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 Set #1 | note |
+--------------------+---------------------------------------------+
| VC0 | video capture for single screen consumer |
| VC1, VC2 | video capture for 2 screen consumer |
| VC3, VC4, VC5 | video capture for 3 screen consumer |
| VC6, VC7, VC8, VC9 | video capture for 4 screen consumer |
| AC0 | audio capture representing all participants |
+--------------------+---------------------------------------------+
If / when a presentation stream becomes active within the conference,
the MCU might re-advertise the available media as:
+----------------+--------------------------------------+
| Capture Set #2 | note |
+----------------+--------------------------------------+
| VC10 | video capture for presentation |
| AC1 | presentation audio to accompany VC10 |
+----------------+--------------------------------------+
11.4. 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 set advertised by the
provider.
A sane, basic, algorithm might be for the consumer to go through each
capture set 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
entries in the video capture sets based either on hard-coded
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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.
11.4.1. One screen consumer
VC3, VC4 and VC5 are all different entries by themselves, not grouped
together in a single entry, 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 loudest region (VC3) or
a switched view with PiPs (VC4). 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.
11.4.2. Two screen 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 (VC3, VC4 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
centre 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 centre streams (one per screen) and the centre 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
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mode.
11.4.3. Three screen consumer configuring the example
This is the most straightforward case - the 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 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. Acknowledgements
Mark Gorzyinski contributed much to the approach. We want to thank
Stephen Botzko for helpful discussions on audio.
13. IANA Considerations
TBD
14. Security Considerations
TBD
15. Informative References
[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.
[RFC3550] Schulzrinne, H., Casner, S., Frederick, R., and V.
Jacobson, "RTP: A Transport Protocol for Real-Time
Applications", STD 64, RFC 3550, July 2003.
[RFC4353] Rosenberg, J., "A Framework for Conferencing with the
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Session Initiation Protocol (SIP)", RFC 4353,
February 2006.
[RFC5117] Westerlund, M. and S. Wenger, "RTP Topologies", RFC 5117,
January 2008.
Appendix A. Open Issues
A.1. Video layout arrangements and centralized composition
In the context of a conference with a central MCU, there has been
discussion about a consumer requesting the provider to provide a
certain type of layout arrangement or perform a certain composition
algorithm, such as combining some number of most recent talkers, or
producing a video layout using a 2x2 grid or 1 large cell with 5
smaller cells around it. The current framework does not address
this. It isn't clear if this topic should be included in this
framework, or maybe a different part of CLUE, or maybe outside of
CLUE altogether.
A.2. Source is selectable
A Boolean variable. True indicates the media consumer can request a
particular media source be mapped to a media capture. Default is
false.
TBD - how does the consumer make the request for a particular source?
How does the consumer know what is available? Need to explain better
how multiple media captures are different from a single media capture
with choices for the source, and when each concept should be used.
A.3. Media Source Selection
The use cases include a case where the person at a receiving endpoint
can request to receive media from a particular other endpoint, for
example in a multipoint call to request to receive the video from a
certain section of a certain room, whether or not people there are
talking.
TBD - this framework should address this case. Maybe need a roster
list of rooms or people in the conference, with a mechanism to select
from the roster and associate it with media captures. This is
different from selecting a particular media capture from a capture
set. The mechanism to do this will probably need to be different
than selecting media captures based on capture sets and attributes.
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A.4. Endpoint requesting many streams from MCU
TBD - how to do VC selection for a system where the endpoint media
consumers want to receive lots of streams and do their own
composition, rather than MCU doing transcoding and composing.
Example is 3 screen consumer that wants 3 large loudest speaker
streams, and a bunch of small ones to render as PiP. How the small
ones are chosen, which could potentially be chosen by either the
endpoint or MCU. There are other more complicated examples also. Is
the current framework adequate to support this?
A.5. VAD (voice activity detection) tagging of audio streams
TBD - do we want to have VAD be mandatory? All audio streams
originating from a media provider must be tagged with VAD
information. This tagging would include an overall energy value for
the stream plus information on which sections of the capture scene
are "active".
Each audio stream which forms a constituent of an entry within a
capture set should include this tagging, and the energy value within
it calculated using a fixed, consistent algorithm.
When a system determines the most active area of a capture scene
(either "loudest", or determined by other means such as a button
press) it should convey that information to the corresponding media
stream consumer via any audio streams being sent within that capture
set. Specifically, there should be a list of active coordinates and
their VAD characteristics within the audio stream in addition to the
overall VAD information for the capture set. This is to ensure all
media stream consumers receive the same, consistent, audio energy
information whichever audio capture or captures they choose to
receive for a capture set. Additionally, coordinate information can
be mapped to video captures by a media stream consumer in order that
it can perform "panel switching" if required.
A.6. Private Information
Do we want a way to include private information?
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Authors' Addresses
Allyn Romanow
Cisco Systems
San Jose, CA 95134
USA
Email: allyn@cisco.com
Mark Duckworth (editor)
Polycom
Andover, MA 01810
US
Email: mark.duckworth@polycom.com
Andrew Pepperell
Langley, England
UK
Email: apeppere@gmail.com
Brian Baldino
Cisco Systems
San Jose, CA 95134
US
Email: bbaldino@cisco.com
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