Re: How to choose the optimal buffer length

Hi Antonio,

You're right that the smallest working buffer size can vary depending on the
type and speed of the machine, the type of browser, etc.  We have talked on
this list about removing the buffer size argument from
createJavaScriptNode() and instead letting the system choose the optimal
buffer size automatically.  Optionally, we could provide a hint as to how
tolerant we would be of glitching which could influence this choice.  I
believe Flash has a different approach where they have an additional
internal buffering which can dynamically increase even while the callback
buffer size remains fixed and could be small.  The disadvantage to that
approach is that the latency becomes unpredictable and can increase over
time, for example during gameplay.  The advantage is that it's dynamically
able to adapt to fix the glitching as it comes up and also let's the user
pick a relatively small callback buffer size if that's convenient for them.

It's clear we need something better than the current approach of simply
picking a buffer size and hoping for the best.  I'm interested in hearing
from people who have experience using the Flash API and their thoughts on
the dynamically increasing internal buffering (with latency implications)...

Cheers,
Chris

On Fri, May 20, 2011 at 9:32 PM, Antonio Josť Villena Godoy <_@
antoniovillena.es> wrote:

>
>  Hello
>
>  I have created a small program:
>
> <!DOCTYPE html><html><head>
> <script type='text/javascript'>
> function buffer(e){
>  if( !(++counter % (0x10000/bufferSize)) ){
>    nt= new Date().getTime();
>    if( counter == (0x20000/bufferSize) ){
>      text+= bufferSize + '->' + parseInt(0x10000 * 1000 / (nt - time)) +
> '\n';
>      e.currentTarget.disconnect();
>      bufferSize<<= 1;
>      if( bufferSize == 32768 )
>        alert(text);
>      else
>        context= new webkitAudioContext(),
>        node= context.createJavaScriptNode(bufferSize, 0, 1),
>        counter= 0x10000/bufferSize - 5,
>        node.onaudioprocess= buffer,
>        node.connect(context.destination);
>    }
>    time= nt;
>  }
>  data1= e.outputBuffer.getChannelData(0);
>  data2= e.outputBuffer.getChannelData(1);
>  for (var i = 0; i < bufferSize; i++)
>    data1[i]= data2[i]= Math.sin(4e3 * (phase++ / context.sampleRate));
> }
> bufferSize= 256;
> context= new webkitAudioContext();
> text= 'SampleRate->' + context.sampleRate + '\n';
> node= context.createJavaScriptNode(bufferSize, 0, 1);
> time= counter= phase= 0;
> node.onaudioprocess= buffer;
> node.connect(context.destination);
> </script></head><body/></html>
>
>  The program sends a sinus wave to the output device at differents buffer
> length. When finishes it shows the results: the original sample rate, and
> the sample speed for each buffer length (from 256 to 16384).
>
>  A similar test is needed in every application, because optimal buffer
> depends on machine performance. So, is possible to add a recommended "buffer
> length value" to specification? Something like context.optimalBufferLength
> or context.recommendedBufferLength
>
>  Regards
>
> --
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>
>

Received on Saturday, 21 May 2011 17:38:13 UTC