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Using the Web Audio API in Web Workers

From: Ashley Gullen <ashley@scirra.com>
Date: Wed, 8 Apr 2015 17:11:12 +0100
Message-ID: <CAABs73ie3tVuPz31zJRv+K=kcG2xjqZ=xd936jUouH2o5J7fvQ@mail.gmail.com>
To: "public-audio@w3.org" <public-audio@w3.org>
We develop a HTML5 game engine and our goal is to ultimately have the
entire engine running from a Web Worker, off the main thread.

There is progress on getting canvas rendering from workers specced. The
last major hurdle to running an entire game engine in a worker is audio
playback. Currently AFAIK Web Audio is only specced to work from the main
thread, and it is a relatively complex API, so if a game engine is running
in a worker there would need to be a bridge between the worker and the main
thread with lots of postMessage going on, which could impact performance
and add latency while adding complexity. Having Web Audio available in Web
Workers would solve this. Has this been investigated yet?

Ideally AudioContext could be made available in WorkerGlobalScope. However
I can immediately see a number of issues:

- integration with Media Elements would not be available (e.g.
createMediaElementSource), because they are part of the DOM which is not
available in a Worker
- integration with Media Streams would not be available, including from
getUserMedia, since these are not available in a Worker (AFAIK)
- selection of audio input and output devices is currently only available
on the main thread (although this may not be a problem if device ID strings
can be posted to the worker)
- ideally types like AudioBuffer would be Transferrable

Implementation ideas:
- a WorkerAudioContext with the unsupported features removed (e.g. anything
using media elements or media streams) but otherwise working identically to
- a WorkerAudioContext with all features, but some way of integrating with
media elements/media streams from the main thread (e.g. by ID
strings/object URLs)
- a WorkerAudioContext with some kind of specialised WorkerMediaStream that
can access an object URL created from the main thread and route audio from
either a media element or media stream to the WorkerAudioContext
- a WorkerAudioContext with all features, including speccing Media Streams
for workers! (possibly very difficult)
- a Transferrable AudioContextProxy that can be obtained from an existing
AudioContext on the main thread and sent to a worker. Calls to
AudioContextProxy would simply be forwarded to the existing AudioContext
similar to what a postMessage implementation would do, so it's really using
the same context. AudioContextProxy would also be missing media
element/media stream features, but these could still be implemented from
the main thread since it can use all features there. This is probably the
simplest solution and significantly reduces the burden of bridging the APIs
in JS (reducing the bridge to only the features necessary to cover media
elements/media streams), but in the long term implementing MediaStreams in
workers seems like it would be desirable too.

Any thoughts?

Ashley Gullen
Received on Wednesday, 8 April 2015 16:11:43 UTC

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