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

Re: questions about direct assignment

From: Robert O'Callahan <robert@ocallahan.org>
Date: Thu, 30 May 2013 09:48:44 +1200
Message-ID: <CAOp6jLb7Hcwk1tAD_8aKjCUiE0x4abTs722vN1VW=gtHfA6H5w@mail.gmail.com>
To: Jim Barnett <Jim.Barnett@genesyslab.com>
Cc: "public-media-capture@w3.org" <public-media-capture@w3.org>
By direct assignment I assume you mean 'srcObject'...

On Thu, May 30, 2013 at 5:47 AM, Jim Barnett <Jim.Barnett@genesyslab.com>wrote:

>  1.       In the case of direct assignment, is currentSrc  null?   The
> HTML5 spec says that if currentSrc is null, there is no media resource, so
> there may be a problem lurking in here.
>

Yes, that spec needs to be clarified. In our implementation, when srcObject
is set, currentSrc returns the empty string. This means that the media
element is not loading its own resource.

**2.       **The HMTL5 spec allows for both the ‘src’ attribute and
> <source> children to be specified, and says that if they both occur, src
> takes precedence.  Do we want want to be consistent with this and allow
> direct assignment to occur with ‘src’ and <source>?  (Direct assignment
> would take precedence.)
>

We have to specify what happens when all of 'srcObject', 'src' and <source>
are present --- we can't stop authors from doing that. Our implementation
makes srcObject take precedence.


> ****
>
> **3.       **For the purposes of cross-origin constraints, what is the
> origin of the MediaStream?
>

That is a very good question! It's up to every API that can produce a
MediaStream to specify what the origin is of that MediaStream, that needs
to be added to at least the gUM and WebRTC specs.

For gUM, the origin of the MediaStream should be the origin of the page
that requested it. For WebRTC PeerConnections, it depends on the WebRTC
security model, and that group should take of that. For MediaStreams
constructed from tracks, we need to do something that merges the origins of
the streams from which each track comes.

Alternatively we could track origins per-track, but that doesn't fit media
elements very well.

****
>
> 4.       Do we say that the Tracks in the MediaStream must also implement
> AudioTrack and VideoTrack interfaces in the HTML5 spec?
>

No. A MediaStreamTrack is a different thing from a media element track. A
MediaStream with MediaStreamTracks feeding into a media element will cause
AudioTrack and VideoTrack objects to be added to the media element.

Rob
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Received on Wednesday, 29 May 2013 21:49:15 UTC

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