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RE: recording proposal

From: Jim Barnett <Jim.Barnett@genesyslab.com>
Date: Sun, 7 Oct 2012 12:45:31 -0700
Message-ID: <E17CAD772E76C742B645BD4DC602CD8106CDFD9F@NAHALD.us.int.genesyslab.com>
To: "Harald Alvestrand" <harald@alvestrand.no>, <public-media-capture@w3.org>
Harald,

Travis and I started with record() attached to MediaStream, but we ran
into problems:

1.       Nothing I see requires that a MediaStream have only a single
video track.  Should recording blend all the video tracks into one
incomprehensible mess?  (The <video> element has a concept of the
'active' or 'primary' video track, but MediaStream doesn't.)

2.       Any form of media processing (e.g., inserting still images into
the video stream is one of the use cases, talking to an ASR system will
be another) requires access to the individual media streams.  

 

As far as I can tell, you need both combined recording and access to the
individual tracks.  If that's the case, it's better to start off with a
Track level API and figure out how to form a combined recording on top
of it, than to start off with a Stream level API and try to extract the
individual tracks from it.  

 

-          Jim

 

From: Harald Alvestrand [mailto:harald@alvestrand.no] 
Sent: Sunday, October 07, 2012 1:40 PM
To: public-media-capture@w3.org
Subject: Re: recording proposal

 

On 10/05/2012 03:55 PM, Jim Barnett wrote:

	partial interface MediaStreamTrack : EventTarget  {
	    void        record
<imap://hta@eikenes.alvestrand.no:143/fetch%3EUID%3E.INBOX.W3C.webrtc.me
dia%3E872#widl-record>  (optional timeSliceType
<imap://hta@eikenes.alvestrand.no:143/fetch%3EUID%3E.INBOX.W3C.webrtc.me
dia%3E872#idl-timeSliceType>  timeSlice);
	    void        stopRecording
<imap://hta@eikenes.alvestrand.no:143/fetch%3EUID%3E.INBOX.W3C.webrtc.me
dia%3E872#widl-stoprecording>  ();

Oops..... I got lost here.

A MediaStreamTrack contains either audio or video.

Recording, for any practical purpose, requires that one records audio
and video together - synchronized, and in some kind of container format.

This also means that the format produced by record() cannot possibly be
compatible with the MediaSource API, since that's a combined format.

I don't think this is what people expect of us.

(I see this is listed under "open issues", but I don't think we should
even start down this path with this fundamental limitation in place.)

                  Harald
Received on Sunday, 7 October 2012 19:46:31 GMT

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