W3C home > Mailing lists > Public > public-media-capture@w3.org > April 2013

Re: Rationalizing new/start/end/mute/unmute/enabled/disabled

From: Robert O'Callahan <robert@ocallahan.org>
Date: Mon, 8 Apr 2013 22:22:35 +1200
Message-ID: <CAOp6jLZu0rj_z8tFYborTRYNTx6mx79fip1Anxaz=Xmx+PsY5g@mail.gmail.com>
To: Stefan Håkansson LK <stefan.lk.hakansson@ericsson.com>
Cc: "public-media-capture@w3.org" <public-media-capture@w3.org>
On Mon, Apr 8, 2013 at 9:47 PM, Stefan Håkansson LK <
stefan.lk.hakansson@ericsson.com> wrote:

> 2. We should define how a saved stream (and perhaps other media files) can
> be converted to a MediaStream. Using the media element is one option, but
> would not meet the requirement of allowing the user to fool the application
> - something we have discussed we should support.

Fooling the application is only relevant for streams generated by
getUserMedia. If an application wants to stream its own saved resource as a
MediaStream, we don't need to let the user interfere with that.

A question on video_element.captureStreamUntilEnded(): does it capture only
> what is rendered, or also tracks that are not played?

All tracks that we can decode. So e.g. if you play a resource with a video
track in an <audio> element and capture that to a MediaStream, the
MediaStream contains the video track.

And for the case of multiple audio tracks: those are mixed by the media
> element when played.
Will those individual tracks be present in the captured MediaStream, or
> will there be just one audio track (representing the mixed audio)?

We don't currently support decoding more than one audio track, but when we
do I think we should represent those as separate tracks in the MediaStream.
The enabled state of those tracks will need to follow the track selections
of the media element --- we haven't thought about how to do that yet.

How well have you specified it, is there text available that could be used?

There was some text in the MediaStream Processing draft. It's not very good

In principle I agree, being able to switch source of a MediaStream(Track)
> would be a natural to have (and needed for certain legacy interop cases).

We may not need to "switch the source of a MediaStreamTrack". There are a
few ways to expose API to effective switch audio sources. One approach
would be to create a MediaStreamTrack from the output of a Web Audio
AudioNode. Then Web Audio can be used to switch from one audio source to
another. Web Audio already specs this:
no-one's implemented it yet AFAIK. It would be easy for us to

(Here you could also have a MediaStream with two video tracks sent to the
> other end, and switch at the target. Maybe not the most natural way, but
> doable.)

Trying do all these effects at the target sounds clumsy, fragile and

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Received on Monday, 8 April 2013 10:23:07 UTC

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