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Re: Multiple destinations in a single AudioContext

From: Olivier Thereaux <Olivier.Thereaux@bbc.co.uk>
Date: Mon, 13 Aug 2012 20:38:32 +0100
Message-ID: <DB2805F7-C003-4C25-AC86-5DC1111E6DF9@bbc.co.uk>
To: Chris Rogers <crogers@google.com>
CC: Audio Working Group <public-audio@w3.org>
That's great Chris, thanks for the pointer. I will update the Implementation Notes for that use case. 


On 13 Aug 2012, at 18:26, "Chris Rogers" <crogers@google.com> wrote:

> On Mon, Aug 13, 2012 at 8:53 AM, olivier Thereaux <olivier.thereaux@bbc.co.uk> wrote:
> Hello,
> As you know, Joe and I have been working on our Use Cases and Requirement document, detailing the specific requirements illustrated by each of our scenario.
> One of the scenario we added a few months ago was that of an "online DJ set".
> The current text of the scenario can be read at:
> http://dvcs.w3.org/hg/audio/raw-file/tip/reqs/Overview.html#connected-dj-booth
> One interesting aspect to the scenario is that it illustrates the need for audio to be sent to two different destinations (headphones + streaming). Even more interestingly, the application needs to switch a given context from one destination to another gradually and seamlessly.
> I cannot quite figure out how that could be done with the current draft of the Web Audio API. Ideally, it would look like this: https://dvcs.w3.org/hg/audio/raw-file/tip/reqs/DJ.png but given the API's constraint on the number of destinations a context can have, that is not possible.
> This might just work:
> https://dvcs.w3.org/hg/audio/raw-file/tip/reqs/DJ2.png
> if a given AudioContext is allowed to have two AudioDestinationNodes in its graph, but only one is connected as destination at any given time. This is a much lesser solution, because the DJ cannot continue listening to headphones as she fades the second track in, but it might just be doable.
> Am I missing an obvious alternative which would make this scenario a possibility? Any thought on how else you'd do it? Note that I am not saying that the API *MUST* enable this scenario - but it is interesting food for thought.
> Olivier
> Hi Olivier, you may have noticed the addition of createMediaStreamSource() to the specification.  It represents a source from a MediaStream, and work is underway in WebKit to support this now, including live audio input.  There will be a matching createMediaStreamDestination() for sending to remote peers.
> For the online DJ case, where headphone output is required in addition to the "main" audio output then multi-channel devices can be supported as described so far in the spec (.numberOfChannels and .maxNumberOfChannels of AudioContext).  We're working hard on implementing that part right now.
> p.s. The W3C server hosting the Web Audio spec seems to be down right now...

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Received on Monday, 13 August 2012 19:39:06 UTC

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