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Re: Stopping a looping source when an envelope cycle has ended

From: Marcus Geelnard <marcus.geelnard@gmail.com>
Date: Mon, 9 May 2016 23:13:03 +0200
To: Raymond Toy <rtoy@google.com>, Paul Adenot <padenot@mozilla.com>
Cc: "public-audio@w3.org" <public-audio@w3.org>
Message-ID: <5730FD5F.3080508@gmail.com>
I filed bugs for Chromium and Firefox:



The example used in the bug reports can be found here: 

My personal feeling/opinion is that either the Web Audio API should take 
care of these kind of things (which could be tricky, given all the 
possible corner cases), or there should be some easy-to-use API for 
catching things like AudioParam automation events (e.g. 
EventQueueEmpty). In general, looping/infinite sources are tricky, 
especially if they are only used for a short period of time (e.g. for a 
single note, as in my example).



Den 2016-05-09 kl. 19:27, skrev Raymond Toy:
> First, what Paul said:  File a bug with the browser.
> However, it seems to me that if you have a looping source, it can 
> never be stopped (unless you stop or disconnect it). Everything it's 
> connected to must continue to process.
> In chrome, we do take some shortcuts if the gain is 0, but probably 
> not when you have automations on the gain.  This would be an 
> optimization that we need to do.
> On Thu, May 5, 2016 at 2:20 PM, Marcus Geelnard 
> <marcus.geelnard@gmail.com <mailto:marcus.geelnard@gmail.com>> wrote:
>     Hi all!
>     I just recently started doing some (almost) serious work with Web
>     Audio, and I'm glad to find that the API and the implementations
>     are moving along nicely!
>     One of the things I have not been able to find a nice solution to
>     yet, though, is a situation that leaks memory and CPU cycles...
>     (I'm sure there's a solution that I have missed)
>     I'm playing an AudioBuffer using a looping AudioBufferSourceNode,
>     followed by a GainNode that acts as an envelope modulator.
>     Now, one AudioBufferSourceNode + GainNode is created and
>     start():ed for each note that I play, and all JS references to the
>     nodes are dropped. Eventually the GainNode will reach zero (when
>     the envelope cycle has ended), but as far as I can tell, the
>     AudioBufferSourceNode will continue sampling and eat CPU cycles.
>     I think that this is correct behavior (the AudioBufferSourceNode
>     has the playing state set, so it will not be GC:ed), although
>     there seems to be a difference between Blink & Gecko w.r.t how
>     much CPU is consumed by all the silent nodes.
>     Question: What is the best method for stopping / disconnecting a
>     looping source node at a predefined AudioContext time (i.e. when
>     the GainNode has finished all the automation events)? I would like
>     to avoid keeping track of all the active nodes myself (e.g. array
>     of active source nodes + polling & checking against currentTime)..
>     /Marcus
Received on Monday, 9 May 2016 22:15:45 UTC

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