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

Rémi Denis-Courmont remi at remlab.net
Fri Jul 24 10:52:42 CEST 2015

Le 2015-07-24 11:04, Sampsa Riikonen a écrit :
> 1) I imagine that error (***) results from the fact, that rtcp
> information is not being read correctly.
>   - Does this assumption make sense?

That would seem rather unlikely. Also RTCP does not have much practical 
effects when receiving a single RTP stream. It is mostly useful for 
cross-stream synchronization.

>   - 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. 
That is up to live555 though.

>   - .. 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.

> 2) As vlc reads the input "streamfile.sdp", what does it do with the 
> file ..
>   - .. passes it "as-is" to live555 ?

Reads it into a buffer and passes the buffer to live555.

>   - .. parses the file, populates an object with parameters and then
> passes that object to live555 ?


>   - Could you please point out where in the vlc/live555 source code
> these things are being done? (tried to find them by myself but no
> success so far..)


>   - 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 

Rémi Denis-Courmont

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