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

[Sigmund Augdal]

On Tue, Feb 01, 2005 at 12:12:40PM -0800, Ross Finlayson wrote:
> 
> >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'?

I might have meen a bit inpresice here, what I wanted to say is that there
are known issues with mpeg2 ts over rtp using the livedotcom module. This is
most likely because this needs a highly experimental demux chaining code
from vlc's core. This code isn't used anywhere else as far as I know.

I did not mean to say that the livedotcom module in general unstable, and
even less anything about live.com libraries.

Hope this clears the air about that.

Sigmund



> 
> 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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