Re: Proposal for MediaTrackCapabilities discovery via enumerateDevices()

Thanks for the input.

I've filed an Issue (#198) 
https://github.com/w3c/mediacapture-main/issues/198 to keep track of the 
resolution.

Discussion should happen here.

Stefan

On 19/06/15 22:21, Joe Berkovitz wrote:
> Hello Media Capture,
>
> This is the second proposal from the Audio WG relating to our earlier
> Last Call requests. It relates to device capabilities discovery. (A
> third, future proposal will address a set of related issues with the
> Audio Output API, but we will skip those questions for now.)
>
> Summary:
>
> The proposed change will allow the MediaDeviceInfos in the array
> returned by enumerateDevices()  to include a new *capabilities*
> attribute of type MediaTrackCapabilities, available _only_ in the
> already-defined case where anti-fingerprinting filtering is not applied.
>
> Rationale:
>
> It is not possible for audio or video applications today to offer the
> user a choice of available devices that takes account of their
> capabilities or characteristics, e.g. channel count, pixel dimensions,
> sample rate, etc.
>
> While it is possible to enumerate devices and obtain their names, kinds
> and opaque IDs, applications also need to  a) filter device lists to
> only include usage-appropriate entries (e.g. only audio inputs >= 44k
> sample rate), or b) display useful information to accompany each
> device's name (e.g. whether it's mono, stereo, etc.). Other use cases
> also exist.
>
> The existing Media Capture API proposal already addresses potential
> fingerprinting exploits by prohibiting the return of device labels
> unless the user has explicitly granted access to at least one device.
> This proposal would apply the same restriction to the return of device
> capabilities.
>
> Proposed changes:
>
> - Add the following attribute to MediaDeviceInfo:
>
>      readonly attribute MediaTrackCapabilities capabilities;
>
> Its definition is as follows:
>
>    * If access to this information is disallowed to the caller, the
> attribute's value is null.
>    * Otherwise, the attribute contains a MediaTrackCapabilities object
> identical to that which would be obtained by the following algorithm:
>        - Let info be the MediaDeviceInfo whose capabilities attribute is
> being determined.
>        - If info.type is "audioinput" or "videoinput",
>          - Call getUserMedia({deviceId: info.deviceId})
>          - If the promise succeeds
>            - Let track be the first MediaStreamTrack in the returned
> MediaStream whose type is "audio" (if the device type was "audioinput")
> or "video" (if the device type was "videoinput").
>            - Assign the attribute's value from track.getCapabilities()
>        - Otherwise if info.type is "audiooutput" the attribute's value
> is a MediaTrackCapabilities describing the capabilities of the audio
> output device (if these can be obtained) or else null.
>
> - Change the description of enumerateDevices() in 9.2.2 as follows:
>
> In step 4, to the text " let filteredList be a copy of resultList, and
> all its elements, where the label member is the empty string", append
> "and the capabilities member is null".
>
> - Change the text of section 9.2.3 (Access control model) as follows:
>
> Modify the text "If access has been granted for a media device, the
> MediaDeviceInfo dictionary will contain the deviceId, kind, label, and
> groupId" to read "If access has been granted for a media device, the
> MediaDeviceInfo dictionary will contain the deviceId, kind, label,
> groupId and capabilities."
>
> Thanks very much for your consideration.
>
> --
> .            .       .    .  . ...Joe
>
> *Joe Berkovitz*
> President
>
> *Noteflight LLC*
> 49R Day Street / Somerville, MA 02144 / USA
> phone: +1 978 314 6271
> www.noteflight.com <http://www.noteflight.com>
> "Your music, everywhere"

Received on Saturday, 20 June 2015 05:03:11 UTC