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Re: Reviewing the Web Audio API (from webrtc)

From: Randell Jesup <randell-ietf@jesup.org>
Date: Thu, 19 Apr 2012 01:04:09 -0400
Message-ID: <4F8F9CC9.4010007@jesup.org>
To: public-audio@w3.org
On 4/18/2012 6:36 PM, Robert O'Callahan wrote:
> On Wed, Apr 18, 2012 at 12:23 PM, Randell Jesup <randell-ietf@jesup.org
> <mailto:randell-ietf@jesup.org>> wrote:
>     So it sounds like to modify audio in a MediaStream you'll need to:
>     * Extract each track from a MediaStream
>     * Turn each track into a source (might be combined with previous step)
>     * Attach each source to a graph
>     * Extract tracks from the destination of the graphs
>     * Extract the video stream(s) from the MediaStream source
>     * Combine all the tracks back into a new MediaStream
> And one of the downsides of doing it this way is that you lose sync
> between the audio and video streams. Usually not by much, but more for
> certain kinds of processing. Given there's a way to not lose sync at
> all, why not use it? Sorry to harp on this :-).

For that matter, you'd (in theory at least) lose sync between audio 
tracks as well.  (In practice if the graphs are identical you probably 
*shouldn't* lose sync, but it's not guaranteed - and what if you want to 
process tracks differently?  (add reverb to background but not 
voice-over, etc.)

Personally, I'd like to see MediaStreams be the primary "container" 
object for media in the HTML5 world, and have things operate on those. 
In that world, a processing node would operate on MediaStreams, and 
within it could have processing graphs, etc.  MediaStream sources can be 
hardware (getUserMedia), HTML5 media objects (<video>, <audio>), complex 
sources (PeerConnections), etc.  MediaStreams can be routed to similar 
sorts of things (minus getUserMedia).  It provides us with a unified 
abstraction of these media flows, instead of a set of 
similar-but-not-the-same ones that require a lot of conversion back and 
forth or make more of a forest of APIs and abstractions to learn.

Randell Jesup
Received on Thursday, 19 April 2012 05:05:09 UTC

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