[whatwg] Audio canvas?

Mathieu HENRI p01 at opera.com
Wed Jul 16 05:18:28 PDT 2008

Dr. Markus Walther wrote:
> I have noted an asymmetry between <canvas> and <audio>:
> <canvas> supports loading of ready-made images _and_ pixel manipulation 
> (get/putImageData).
> <audio> supports loading of ready-made audio but _not_ sample manipulation.
> With browser JavaScript getting faster all the time (Squirrelfish...), 
> audio manipulation in the browser is within reach, if supported by rich 
> enough built-in objects.
> Minimally, sample-accurate methods would be needed to
> - get/set a sample value v at sample point t on channel c from audio
> - play a region from sample point t1 to sample point t2
> (Currently, everything is specified using absolute time, so rounding 
> errors might prevent sample-accurate work).
> More powerful methods might cut/add silence/amplify/fade portions of 
> audio in a sample-accurate way.
> It would be OK if this support were somewhat restricted, e.g. only for 
> certain uncompressed audio formats such as PCM WAVE.
> Question: What do people think about making <audio> more like <canvas> 
> as sketched above?

My understanding of HTMLMediaElement is that the currentTime, volume and 
playbackRate properties can be modified live.

So in a way Audio is already like Canvas : the developer modify things 
on the go. There is no automated animations/transitions like in SVG for 

Doing a cross fade in Audio is done exactly the same way as in Canvas.

> -- Markus

Mathieu 'p01' HENRI
JavaScript developer, Opera Software ASA

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