Resolution Constraints in Web Real Time Communications
draft-alvestrand-constraints-resolution-00

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Network Working Group                                      H. Alvestrand
Internet-Draft                                                    Google
Intended status: Informational                           August 26, 2012
Expires: February 27, 2013

         Resolution Constraints in Web Real Time Communications
               draft-alvestrand-constraints-resolution-00

Abstract

   This document specifies the constraints necessary for a Javascript
   application to successfully indicate to a browser that supports
   WebRTC what resolutions it desires on a video stream.

Requirements Language

   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].

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 February 27, 2013.

Copyright Notice

   Copyright (c) 2012 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

   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

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   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
     1.1.  Disposition of this text  . . . . . . . . . . . . . . . . . 3
   2.  Usage considerations  . . . . . . . . . . . . . . . . . . . . . 3
   3.  Usage examples  . . . . . . . . . . . . . . . . . . . . . . . . 4
     3.1.  Examples with GetUserMedia  . . . . . . . . . . . . . . . . 4
     3.2.  Possible SDP mappings . . . . . . . . . . . . . . . . . . . 5
   4.  IANA Considerations . . . . . . . . . . . . . . . . . . . . . . 5
   5.  Security Considerations . . . . . . . . . . . . . . . . . . . . 6
   6.  Acknowledgements  . . . . . . . . . . . . . . . . . . . . . . . 6
   7.  References  . . . . . . . . . . . . . . . . . . . . . . . . . . 6
     7.1.  Normative References  . . . . . . . . . . . . . . . . . . . 6
     7.2.  Informative References  . . . . . . . . . . . . . . . . . . 7
   Author's Address  . . . . . . . . . . . . . . . . . . . . . . . . . 7

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1.  Introduction

   There are a number of scenarios where it's useful for a WebRTC
   application to indicate to the WebRTC implementation in the supported
   browser what the desired characteristics of a video stream are.
   These include, but are not limited to:

   o  Specifying a minimum desired resolution for a given application,
      in order to control the user experience or resource tradeoffs made
      by the browser to favour a particular stream

   o  Specifying a maximum desired resolution for a given stream, in
      order to save some resource (bandwidth, CPU....), possibly outside
      of the browser where the browser can't tell that it's exceeding a
      constraint

   o  Specifying resolutions that are a reasonable fit for the current
      usage of the video stream, for instance fitting with the number of
      pixels available on the part of a device's display surface that is
      devoted to displaying this video stream

   o  Specifying the shape of a video stream, in order to fit the video
      onto a display surface without the need for black bars or image
      distortion

   Similar considerations apply for framerate.

1.1.  Disposition of this text

   This draft is written in order to get something specific out to refer
   to during spec-writing and implementation.  The text may eventually
   get merged into either the IETF document on SDP usage by RTCWEB, or
   the W3C WEBRTC document on PeerConnection.

2.  Usage considerations
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