[Webkit-unassigned] [Bug 75119] AudioBufferSourceNode and MediaElementAudioSourceNode should support multi-channel > stereo

[bugzilla-daemon at webkit.org]

https://bugs.webkit.org/show_bug.cgi?id=75119





--- Comment #5 from Chris Rogers <crogers at google.com>  2012-01-03 17:49:19 PST ---
(In reply to comment #4)
> (In reply to comment #3)
> > Hi James, thanks for offering to do this.  I think it's something you could probably tackle.  But we'll have to first sort out the details of your other vsmul() optimizations in that same part of the code.  If you see my latest comment there, I think we should maybe simplify the denormal handling:
> > 
> > https://bugs.webkit.org/show_bug.cgi?id=75334
> > 
> > As far as the 5.1 to stereo case, the only question is the exact scaling factors (constant multipliers), so you can prepare a patch with close to the exact code (except the numeric values) and we can sort that out later.
> 
> roger, thanks for the guidance. I will work on #75334 firstly. 
> 
> for up and down mixing, for source and destination, we both have 5 options: mono, stereo, quad, 5.0, 5.1.  Current we only have 3 options: mono->mono, mono->stereo, stereo->stereo. 
> 
> do we need to support all channel up and down mixing(that is all 25 options)?

We don't have to support all of them to start with.  After all we only currently support a few of them, so anything is an improvement.  Quad (4-channels) we can probably skip for now (and get to it later).  Also, the most important are the up-mixing options (as opposed to down-mixing).  For up-mixing to a number of channels which isn't known as having a specific channel layout such as 3 channels (which isn't 1,2,4,6 - for mono,stereo,quad,5.1) , the default up-mix should just be to copy/sum the channels into the first available channels, and then just ignore (or zero) the remaining channels.

For example, if up-mixing stereo to 3 channels:
channel0 -> channel0
channel1 -> channel1
ignore/silence -> channel2

This type of up-mix may also be interesting for 1,2,4,6, but we don't have to worry about that for now.

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