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Re: Web Audio WG feedback LC-3023 (Re: Media Capture and Streams Last Call review)

From: Joe Berkovitz <joe@noteflight.com>
Date: Fri, 15 May 2015 11:24:56 -0400
Message-ID: <CA+ojG-aXOFxeRT=Rz_2cqfJ5XdJT0wRv6tndbK7WGXYyTS_YYQ@mail.gmail.com>
To: Audio Working Group <public-audio@w3.org>
Before responding to Harald, I'd like to solicit some discussion within the
Audio WG. I think the most important questions here are:

1. If we want to be able to find out properties of devices in an enumerated
list without requesting device access from the user, then what is the
absolute "must have" set of properties for Web Audio to include in
enumerateDevices() results? The more we ask for, the less likely we will
get them -- and some may be more likely to generate long debates than
others, like HDMI.

2. Do we need to enumerate devices, or is it OK for us to use
getUserMedia() with constraints on these properties, and then pass the
deviceID of the returned mediaStream -- obtained with
mediastream.getCapabilities() --  that matches those constraints to an
AudioContext constructor? (As opposed to using
createMediaStreamDestination(mediaStream) which would have the various
sample rate issues raised by Chris).

---------- Forwarded message ----------
From: Harald Alvestrand <harald@alvestrand.no>
Date: Fri, May 15, 2015 at 7:12 AM
Subject: Web Audio WG feedback LC-3023 (Re: Media Capture and Streams Last
Call review)
To: Joe Berkovitz <joe@noteflight.com>, Stefan Håkansson LK <
stefan.lk.hakansson@ericsson.com>, public-media-capture@w3.org, Audio
Working Group <public-audio@w3.org>

Hello, and thanks for your input!

I'm seriously in two minds about this - on one hand, it seems like
functionality that is well worth having.

On the other hand, it seems like a long list of things that could be of
interest here, and I can easily envision considerable time passing while
we discuss the details of each (for instance, if we expose the fact that
an output is HDMI, we also expose the fact that it's either crypto
capable or not crypto capable....)

I think a lot of things can be addressed within the
capabilities/constraints/settings model we've adopted for getUserMedia -
one can define new constraints that get you the selectivity you want,
one can call getCapabilities() to figure out what kind of device one
has, one can use getSettings() to figure out what the current state of
play is. If so (and if the TF keeps the "registry" approach for
constraints), solving these problems can be as easy as authoring an
add-on document called "additional audio capabilities and constraints".

But I'm not sure if that will cover all your needs, or if this is the
most elegant way of doing it - certainly some will make immediate note
that the constraints mechanism isn't what they consider elegant.

What do you see as the best way forward here - aim to address this
later, or do we have parts of this problem that we *have* to address now?


Den 21. april 2015 20:59, skrev Joe Berkovitz:
> Hello Stefan,
> Thank you for your recent solicitation of feedback to on the Media
> Capture and Streams API, which I passed to the Web Audio Working Group.
> The Web Audio WG so far has identified one key item that we would like
> to see addressed. The MediaDeviceInfo result from enumerateDevices()
> (
> lacks information that is typically available in the underlying OS
> implementations that we think would be very helpful for implementations:
> __ __
> __·         __Channel count and configuration (Mono, Stereo, 5.1, 7.1,
> etc…)____
> __·         __Physical Output (Headphone, Speaker, HDMI, …)____
> __·         __Latency (this matters a lot for gaming -- it will be very
> low for on-board hardware, perhaps quite high for wireless audio
> bridging like Apple TV)____
> __·         __Output capabilities (bitstream passthrough vs PCM –
> relevant in digital media adapter cases (Chromecast, etc))____
> It is perhaps sufficient from a user interface point of view to have a
> string to display, but for a program to be able to either adapt to the
> user selection or to guide and default the user selection, the above are
> pretty important characteristics, at least in some use cases. Many if
> not most of the host OSes that user agents run on expose these sorts of
> output device characteristics. ____
> Aside from the difficulty with enumerating devices, there is also
> perhaps a need to make it possible for applications to query the set of
> available devices with respect to the above
> charateristics. MediaTrackConstraints and MediaTrackSettings do not
> currently  include constraint attributes that map to items in the above
> list. And even if they do, arriving at a practical goodness-of-fit
> metric that can be generalized across a spectrum of audio apps may be
> difficult.
> The same concerns apply to the set of input devices.__
> __ __
> Please let us know if this issue makes sense to the group and can be
> addressed within the timeframe of the coming run-up to a Last Call WD.
> We'd be happy to arrange some sort of inter-WG call to try to make
> progress on this together.
> Thank you!
> Best regards,
> Joe Berkovitz
> co-chair Web Audio WG
> *Noteflight LLC*
> Boston, Mass.
> phone: +1 978 314 6271
> www.noteflight.com <http://www.noteflight.com/>
> "Your music, everywhere"
> On Wed, Apr 15, 2015 at 1:31 AM, Stefan Håkansson LK
> <stefan.lk.hakansson@ericsson.com
> <mailto:stefan.lk.hakansson@ericsson.com>> wrote:
>     The WebRTC and Device APIs Working Groups request feedback on the Last
>     Call Working Draft of Media Capture and Streams, a JavaScript API that
>     enables access to cameras and microphones from Web browsers as well as
>     control of the use of the data generated (e.g. rendering what a camera
>     captures in a html video element):
>     http://www.w3.org/TR/2015/WD-mediacapture-streams-20150414/
>     The groups have identified the following other W3C Working Groups as
>     likely sources of feedback:
>     - HTML Working Group, especially the HTML Media Task Force, as our API
>     extends the HTMLMediaElement interface and defines a new type of media
>     input via MediaStream
>     - WebApps Working Group, especially on the overall usage of Web IDL
>     the definition of error handling
>     Audio Working Group, as the Web Audio API builds upon the MediaStream
>     interface
>     - WAI Protocol and Formats Working Group, especially on the impact of
>     the user consent dialog and the applicability of the indicators of
>     device usage in assistive tools
>     - Web and TV Interest Group, as the manipulation of media input can be
>     relevant to some of their use cases (e.g. glass to glass)
>     - Web App Security Working Group, especially on our links between
>     secured origins and persistent permissions, and our current policy
>     regard to handling access to this "powerful feature"
>     - Web Security Interest Group, especially on our security
>     Privacy Interest Group, as access to camera and microphone has strong
>     privacy implications
>     - Technical Architecture Group, for an overall review of the API,
>     especially the introduction of the concept of a IANA registry-based
>     constraints system, the use of promises, and our handling of
>     permissions
>     We naturally also welcome feedback from any other reviewers.
>     The end of last call review for this specification is set to May 15
>     2015; should that deadline prove difficult to meet, please get in
>     so that we can determine a new deadline for your group.
>     As indicated in the document, comments should be sent to the
>     public-media-capture@w3.org <mailto:public-media-capture@w3.org>
>     mailing list.
>     Thanks,
>     Frederick Hirsch, Device APIs Working Group Chair,
>     Harald Alvestrand and Stefan Hakansson, WebRTC Working Group Chairs
>     Media Capture Task Force Chairs
> --
> .            .       .    .  . ...Joe
> *Joe Berkovitz*
> President
> *Noteflight LLC*
> Boston, Mass.
> phone: +1 978 314 6271
> www.noteflight.com <http://www.noteflight.com>
> "Your music, everywhere"

.            .       .    .  . ...Joe

*Joe Berkovitz*

*Noteflight LLC*
49R Day Street / Somerville, MA 02144 / USA
phone: +1 978 314 6271
"Your music, everywhere"
Received on Friday, 15 May 2015 15:25:25 UTC

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