[whatwg] Type strings to specify number of AAC audio channels

Ian Hickson ian at hixie.ch
Wed Nov 27 16:27:13 PST 2013

On Mon, 23 Sep 2013, Bolin Hsu wrote:
> Since the royalty for decoding surround sound AAC is higher than stereo 
> AAC, some platforms can decode stereo AAC but not surround sound AAC. 
> But the type string passed to HTMLMediaElement.canPlayType(type) doesn't 
> specify number of channels. I discussed this with some colleagues before 
> I found this list. Has this been covered by standard? Below are some 
> ideas came up during discussion:
> - Use a new codec string, such as 
> HTMLMediaElement.canPlayType('audio/mp4; codecs="aac51"')
> - Add a new parameter, such as
> HTMLMediaElement.canPlayType('audio/mp4; codecs="mp4a.40.2", channels="6")

These seem like appropriate approaches. They would merely need updates to 
the relevant RFCs.

> - Add new element for platform configuration. Some platforms can only
> output stereo audio, so the surround sound is down mixed to stereo. This
> can potentially query the platform if it can really output 6 simultaneous
> audio streams, amount other things:
> HTMLNewElement.getCapability('audio')

I don't think this would be appropriate for an element. As an API, it's a 
client capability query, which, if we support it, would probably belong to 
an API for doing such things. Not sure what the right spec would be for 
that. Anyone?

Ian Hickson               U+1047E                )\._.,--....,'``.    fL
http://ln.hixie.ch/       U+263A                /,   _.. \   _\  ;`._ ,.
Things that are impossible just take longer.   `._.-(,_..'--(,_..'`-.;.'

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