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Re: Proposal to include channelCount constraint/capability

From: Harald Alvestrand <harald@alvestrand.no>
Date: Fri, 19 Jun 2015 10:18:17 +0200
Message-ID: <5583D049.2080705@alvestrand.no>
To: Joe Berkovitz <joe@noteflight.com>, public-media-capture@w3.org
CC: Audio Working Group <public-audio@w3.org>
Thank you!

I've filed this as issue #197 in the issue tracker:

https://github.com/w3c/mediacapture-main/issues/197

Discussion shoud happen on the list, but the issue tracker is used to 
keep track of what we think the resolution is.


On 06/19/2015 12:21 AM, Joe Berkovitz wrote:
> Summary:
>
> The proposed change will associate a channel count with an audio 
> MediaTrack, allowing both device discovery (via constraints) and 
> device description (via capabilities and settings) to account for the 
> number of audio channels in a track.
>
> Rationale:
>
> Channel counts are fundamental descriptors of audio tracks, as width 
> or height are fundamental to video tracks (for input, at any rate). 
> Knowing the potential and real channel counts of device streams are 
> essential for audio-based apps to present or make meaningful choices 
> between devices, and to adjust an application's behavior to best fit a 
> given device.
>
> The Audio WG did consider using an enumerated type for channel layouts 
> (e.g. "mono", "5.1", etc.) but has settled on channel counts because 
> they are always knowable and discoverable in the UA's native 
> environment, while knowledge of actual channel layouts are neither 
> universally available nor standardized. Channel layout constraints 
> could be added in the future if needed.
>
> Definitions:
>
> The channel count of an audio track is the number of independent 
> channels of sound that it contains, i.e. the number of audio samples 
> per sample frame.
>
> Proposed changes:
>
> - Add a *boolean channelCount* attribute to 
> MediaTrackSupportedConstraints.
> - Add a *long channelCount* attribute to MediaTrackSettings
> - Add a *long/LongRange channelCount* attribute to MediaTrackCapabilities
> - Add a *ConstraintLong channelCount* attribute to MediaTrackConstraintSet
>
> Thank you very much for your consideration.
Received on Friday, 19 June 2015 08:18:51 UTC

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