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RE: tvapi-ACTION-25: Look at the timeshifting requirements and the html video element

From: HU, BIN <bh526r@att.com>
Date: Mon, 16 Mar 2015 20:45:53 +0000
To: Chris Needham <chris.needham@bbc.co.uk>, TV Control API Community Group <public-tvapi@w3.org>
Message-ID: <179FD336116F754C876A9347238FE29A02851166@CAFRFD1MSGUSRIA.ITServices.sbc.com>
Thank you Chris for looking into this.

It seems to me that a change to Media Capture and Streams to allow buffering by the User Agent makes it easier to meet our requirement.

Do you or does anyone know the rational of current "The User Agent must not buffer data from a MediaStream"?

Thanks
Bin

-----Original Message-----
From: Chris Needham [mailto:chris.needham@bbc.co.uk] 
Sent: Monday, March 16, 2015 7:49 AM
To: TV Control API Community Group
Subject: tvapi-ACTION-25: Look at the timeshifting requirements and the html video element

Hi all,

An action I took from the last meeting was to investigate support for the timeshift requirements [1].

Pause and resume are supported by the HTMLMediaElement [2, 3], but when used with a MediaStream object, constraints are applied [4] that are relevant to timeshifted playback. The MediaStream spec says: "The User Agent must not buffer data from a MediaStream. When playing, the User Agent must always play the current data from the stream." This disallows pausing, and as the MediaStream is not seekable, and the playbackRate must be 1.0, it also prevents the user from fast-forwarding or rewinding through time-shifted content.

Our requirements mapping table [5] says timeshifting could be done using the MediaStream Recording API [6], but this would mean users implementing it in JavaScript rather than it being directly supported by the platform. The considerations are similar to those Paul found with regard to the recording requirements [7], e.g., use of the timeslice parameter and ondataavailable event. An application would then, I think, have to use Media Source Extensions to play the timeshifted media.

I wonder whether the MediaStream Recording API is the right approach here, or whether we should propose a change to Media Capture and Streams to allow buffering by the User Agent?

Chris

[1] http://www.w3.org/community/tvapi/wiki/Main_Page/Technical_Requirement
[2] http://www.w3.org/html/wg/drafts/html/master/semantics.html#dom-media-pause
[3] http://www.w3.org/html/wg/drafts/html/master/semantics.html#dom-media-play
[4] http://w3c.github.io/mediacapture-main/#media-element-attributes-when-playing-a-mediastream
[5] http://www.w3.org/community/tvapi/wiki/Main_Page/Requirements_Mapping
[6] http://www.w3.org/TR/mediastream-recording/
[7] https://lists.w3.org/Archives/Public/public-tvapi/2015Feb/0008.html

________________________________________
From: TV Control API Community Group Issue Tracker [sysbot+tracker@w3.org]
Sent: 17 February 2015 14:36
To: public-tvapi@w3.org
Subject: tvapi-ACTION-25: Look at the timeshifting requirements and the html video element

tvapi-ACTION-25: Look at the timeshifting requirements and the html video element

http://www.w3.org/community/tvapi/track/actions/25

Assigned to: Chris Needham
Received on Monday, 16 March 2015 20:46:47 UTC

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