- From: Grant Galitz <grantgalitz@gmail.com>
- Date: Mon, 11 Jul 2011 02:11:22 -0400
- To: public-audio@w3.org
- Message-ID: <CAD8zUBaJHKiFebNe41tyJ=Hh4uSj8z+C2LkHwtYgZ0486z0J8g@mail.gmail.com>
I'll briefly compare the mozilla audio data api and the web audio api and run through this list of what can be improved upon in web audio. - Web Audio does not allow resampling, this is a major thorn in probably a couple people's butts, because I have to do this in JavaScript manually. If there is a security concern for bottlenecking, then I'd assume we could throw in some implementation-side limitations on the number of concurrent supposed resampling nodes that could be run at the same time. - Web Audio forces the JavaScript developer to maintain an audio buffer in JavaScript. This applies for audio that cannot be timed to the web audio callback, such as an app timed by setInterval that has to produce x samples every x milliseconds. The Mozilla Audio Data API allows the JS developer to push samples to the browser and let the browser manage the buffer on its own. The callback grabbing x number of samples every call is not a buffer on its own, that's the callback sampling the whole buffer of what I'm talking about. Buffer ring management in JavaScript takes up some CPU load and it would always be better in my opinion to let the browser manage such a task. - "The callback method knows how often to fire," this is a fallacy, even flash falls for this issue and can produce clicks and pops on real-time generated audio (Even their docs hint at this). This is because by the time the callback API figures out a delay, its buffering may be premature due to previous calculations and may as a result gap the audio. It is imperative you let the developer control the buffering process, since only the developer would truly know how much buffering is needed. Web Audio in chrome gaps out for instance when we're drawing to a canvas stretched to fullscreen and a canvas op takes a few milliseconds to perform, to a reasonable person this would seem inappropriate. This ties in basically with the previous point of letting the browser manage the buffer passed to it, and allowing the JS developer to buffer ahead of time rather than having a real-time thread try to play catch-up with an inherently bad plan. - Building up on the last point, in order to achieve ahead-of-time buffering, I believe it would be wise to either introduce a stub function that allows samples to be added at any time without waiting for a callback, just like mozWriteAudio, OR to allow the callback method to be called when buffering reaches a specified low point *specified* by the developer. This low point is not how many samples are to be sent to the browser each callback, but lets the API know WHEN to fire the callback, with the firing being at a certain number of samples before buffer empty. I hope we can use some or all of these points listed in providing a proper API for real-time generated audio output in JavaScript in a 21st century browser. :D
Received on Monday, 11 July 2011 06:11:49 UTC