[vlc-devel] bug in reading rtcp information from .sdp files ?

Ross Finlayson finlayson at live555.com
Fri Jul 24 11:03:15 CEST 2015

>>  - If vlc does not have access to rtcp/rtp packets, does it default
>> back to some other (lame-)scheme of measuring the time, say, the
>> arrival time of the packets/frames, etc.?
> If RTCP is unavailable, I presume live555 falls back to RTP timestamps.


>>  - .. wouldn't it be cool if vlc would, in such a case, inform about
>> this behaviour (i.e. by printing "using xxx scheme for timing", etc.)?
> I don't know how exactly live555 deals with this. But the lack of RTCP should have no bearing on intra-stream buffering.

yes, Rémi is correct here.

>>  - Do I need to specify the rtcp port in the .sdp file, say
>> "a=rtcp:50507", or is it calculated automagically as the media rtp
>> port + 1 ?
> It should work either way, but this is really up to live555 implementation.

Right now the LIVE555 library doesn’t recognize the “a=rtcp:” SDP attribute; instead it (if “a=rtcp-mux” is not present) assumes that RTP will use the even port, and RTCP will use the odd port (i.e., even port+1).

But anyway, as Rémi noted, if you have only a single stream (e.g., video only), then RTCP is pretty much irrelevant to VLC, so focusing on it is a ‘red herring’.  Your problem is simply that you have a crappy network.  (You may, however, be able to compensate somewhat for this by increasing VLC’s buffering; there’s a configuration option somewhere for this.)

Ross Finlayson
Live Networks, Inc.

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