[vlc] Re: How RTP timestamps are used by VLC

[Ross Finlayson]

>VLC can also read ts in rtp through the livedotcom module. This is much less
>stable and can probably cause the problems described. You should try to make
>vlc not use the livedotcom module for ts streams.

Excuse me, but in what way is the 'livedotcom' module 'much less stable'?

If his incoming stream is a MPEG Transport Stream over RTP (or anything 
else over RTP), then the 'livedotcom' module is exactly what should be 
used.  As with all RTP streams, the 'presentation timestamp' (the "pts" 
parameter that's passed to "StreamRead()" in "livedotcom.cpp") is computed 
from each packet's RTP timestamp, using information in periodic RTCP 
'Sender Report' (SR) packets that map the RTP timestamp to real, 'wall 
clock' time.  (This computation of the 'presentation timestamp' is done by 
the LIVE.COM library code, not by the "livedotcom.cpp" code.)

So, the problem that the original poster (Dennis Darcy) had was apparently 
due to problems that VLC had with the "pts" parameter to "StreamRead()" - 
in the special case when the input stream was a MPEG Transport Stream (over 
RTP).  It turns out, though, that rendering MPEG Transport Stream data - 
because it contains its own timing information - does not need the 
presentation timestamps that are computed from the RTP timestamps.  (This 
is not true in general, but just for MPEG Transport Stream data.)

So, perhaps there should be code added somewhere to VLC (either to 
"livedotcom.cpp" or higher-level code that uses it) that tells it to ignore 
the "pts" timestamps if the input data is from a MPEG Transport Stream?


	Ross Finlayson
	LIVE.COM
	<http://www.live.com/>

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