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Multiple destinations in a single AudioContext

From: olivier Thereaux <olivier.thereaux@bbc.co.uk>
Date: Mon, 13 Aug 2012 16:53:11 +0100
Message-Id: <08998F5A-6F7A-469A-BEEC-D59A609E9FD1@bbc.co.uk>
To: Audio Working Group <public-audio@w3.org>
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

Received on Monday, 13 August 2012 15:53:36 GMT

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