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Re: [mediacapture-main] Clarify getUserMedia({audio:{deviceId:{exact:<audiooutput_device>}}}) in this specification mandates capability to capture of audio output device - not exclusively microphone input device (#650)

From: guidou via GitHub <sysbot+gh@w3.org>
Date: Wed, 11 Dec 2019 04:51:12 +0000
To: public-webrtc-logs@w3.org
Message-ID: <issue_comment.created-564378758-1576039871-sysbot+gh@w3.org>
> > The actual question I have is why would a reader conclude that it would be possible for getUserMedia() to capture from output devices when its definition mentions only input devices.
> 
> Because
> 
> > `MediaDeviceKind` Enumeration description
> > `audiooutput` | Represents an audio output device; for example a pair of headphones.
> 
> at least amends, if not repeals and substitutes for
> 
> > Note that this document describes the use of microphone and camera type sources only
> 
> by implication.

There is no amendment or substitution at all, or anything that implies it.

The MediaDeviceKind part that you mention is in Section 9, which defines enumerateDevices() (not getUserMedia). The definition of enumerateDevices() explicitly states that it allows querying input and output devices. 

getUserMedia() is defined in a different section that says it deals with input devices (not output). Results are returned as MediaStream/MediaStreamTrack. The only supported sources for those MediaStreamTracks are microphones or webcams (i.e., input devices only) and those are the only sources supported in this spec. 

Note that enumerateDevices does not deal at all with MediaStreamTracks or sources, while getUserMedia does not deal at all with MediaDeviceKind. There is no way to interpret from the spec text that one substitutes the other.

In short, output devices are mentioned only for enumerateDevices() and are not mentioned anywhere as possible sources for MediaStreamTracks/getUserMedia.

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Received on Wednesday, 11 December 2019 04:51:13 UTC

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