Subject: [rtcweb] Using PAUSED to trigger API event

From: Magnus Westerlund <[email-masked]>
Date: Thu, 26 Jul 2012 15:12:36 +0200

Hi,
(as individual)

Bo and I have a proposal in AVTEXT for an RTCP based mechanism for RTP
Media stream pause and resume.
https://datatracker.ietf.org/doc/draft-westerlund-avtext-rtp-stream-pause/

This will be discussed in the AVTEXT session on Thursday 17.30 in
Regency E.

The reason I am bring this up for WebRTC is that we think it can
actually resolve one potential issue between the media transport
protocol and the API. A media sender in RTP can stop sending a media
stream at any point in time. This may be the result of a sender side
Disable on the media stream track using the API. In the case of
centralized media servers it could be that server that stops
distributing that media stream based on lack of input or adaptation
control.

What I believe to be a potential issue is that the media receiving
browser will not get any explicit indication that the discontinued
transmission happened at the source and was intentional. The reason a
receiver isn't receiving a media stream could be that the packets get
lost en-route.

Thus a question arise in how the receiving browser knows when to trigger
the event indicating that mediaStream track has stopped. It can clearly
be timer-based but that timer needs to be sufficiently robust to rarely
misclassifying transport interruptions from an actual intentional media
delivery stop.

Thus I propose that this could be improved significantly by having media
senders use the PAUSED indication from
draft-westerlund-avtext-rtp-stream-pause to indicate to the media
receiver that yes, this was an intentional halt in media delivery. Thus
enabling a triggering of the event immediately when the last media is
being processed/displayed rather than later after some timeout has
occurred. Thus greatly improving the applications possibility to remove
blank video displays, reconfigure the GUI etc based on the current
availability of media streams.

Comments and views?

Cheers

Magnus Westerlund

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