W3C home > Mailing lists > Public > public-webrtc@w3.org > November 2011

Proposal: Media streams, media stream tracks and channels

From: Harald Alvestrand <harald@alvestrand.no>
Date: Tue, 08 Nov 2011 01:15:16 +0100
Message-ID: <4EB87494.7090107@alvestrand.no>
To: "public-webrtc@w3.org" <public-webrtc@w3.org>
Discharging a task taken on at the TPAC meeting, some possible words on 
what a media stream, a media stream track or a channel is....

This is based on the introduction section in section 3.1 of the current 
API editors' draft.

The|MediaStream 
<http://dev.w3.org/2011/webrtc/editor/webrtc.html#mediastream>|interface 
is used to represent streams of media data, typically (but not 
necessarily) of audio and/or video content, e.g. from a local camera or 
a remote site. The data from a|MediaStream 
<http://dev.w3.org/2011/webrtc/editor/webrtc.html#mediastream>|object 
does not necessarily have a canonical binary form; for example, it could 
just be "the video currently coming from the user's video camera". This 
allows user agents to manipulate media streams in whatever fashion is 
most suitable on the user's platform.

Each|MediaStream 
<http://dev.w3.org/2011/webrtc/editor/webrtc.html#mediastream>|object 
can represent zero or more tracks, in particular audio and video tracks. 
Tracks can contain multiple channels of parallel data; for example a 
single audio track could have nine channels of audio data to represent a 
7.2 surround sound audio track.

<new text below>

All tracks in a MediaStream are presumed to be synchronized at some 
level. Different MediaStreams may or may not be synchronized.

Each track represented by a|MediaStream 
<http://dev.w3.org/2011/webrtc/editor/webrtc.html#mediastream>|object 
has a corresponding|MediaStreamTrack 
<http://dev.w3.org/2011/webrtc/editor/webrtc.html#mediastreamtrack>|object.

A MediaStreamTrack represents content comprising one or more channels, 
where the channels have a defined well known  relationship to each other 
(such as a stereo or 5.1 audio signal), and may be encoded together for 
transmission as, for instance, an RTP payload type.

A channel is the smallest unit considered in this API specification.

<end new text>

Would including this text help add any clarity after our discussions at 
TPAC?

Query: What other examples of embedded channels would be useful to add? 
Are there good examples of audio or non-audio data embedded in video tracks?

                 Harald
Received on Tuesday, 8 November 2011 00:15:46 UTC

This archive was generated by hypermail 2.3.1 : Monday, 23 October 2017 15:19:26 UTC