[vlc-devel] commit: Remove non-sensical NPT computation code from c9569b35.

[Ross Finlayson]

>This is an entire session for that URL. it starts playing, and after a 
>couple of secs I execute a seek. Obviously some of those PTS values 
>are out of whack.

Yes, this stream is real weird.  Looking at the PTSs for the audio 
stream only, we see that all of the diffs are 96000 microseconds, 
except for the following:

[00000403] live555 demux debug: PTS 1216933811532764, diff for track 
mp4a, is now: -7004189878605393497

This is just initialization => OK

[00000403] live555 demux debug: PTS 1216933810096000, diff for track 
mp4a, is now: -1436764

This is the transition between unsynched and (RTCP)synced PTSs => OK

[00000403] live555 demux debug: PTS 1216933817096000, diff for track 
mp4a, is now: -7400000
[00000403] live555 demux debug: PTS 1216933824096000, diff for track 
mp4a, is now: -7400000
[00000403] live555 demux debug: PTS 1216933831096000, diff for track 
mp4a, is now: -7112000
[00000403] live555 demux debug: PTS 1216933838096000, diff for track 
mp4a, is now: -2696000

WTF?  Why is the server reducing the PTS by several seconds at a 
time?  I have no idea, but the server seems to be broken.

[00000403] live555 demux debug: PTS 1216933845096000, diff for track 
mp4a, is now: 88000
[00000403] live555 demux debug: PTS 1216933852096000, diff for track 
mp4a, is now: 88000

These are probably just the result of minor clock sync adjustments at 
the server end => OK

[00000403] live555 demux debug: PTS 1216934815648000, diff for track 
mp4a, is now: 960672000

This is the jump that occurred after you did the seek.  You had 
played the stream for about 44 seconds, and then requested a seek to 
start at point (roughly) 1030 seconds, so that would be a jump of 986 
seconds.  That's a bit different from the PTS jump that we actually 
saw (960 seconds), but it kinda makes sense...

[00000403] live555 demux debug: PTS 1216934815648000, diff for track 
mp4a, is now: -1344000

Again, WTF?  Why is the server reducing the PTS by more than 1 second??

[00000403] live555 demux debug: PTS 1216933859096000, diff for track 
mp4a, is now: -963656000

Arggh!!  WTF is this server doing??  This makes no sense to me!!

The bottom line is that this server is broken.  I don't know why, but 
it might have something to do with the fact that it's part of an 
Akamai content distribution network.

In any case, it seems that - to handle such streams - VLC (and other 
RTSP/RTP clients) need to watch for unusually large changes in PTS, 
and reset the PTS->PCR mapping accordngly.

What's strange, though, is that when I tried playing the same stream 
recently (using the "openRTSP" client, without seeking), I didn't see 
any unusual PTS changes (for either the audio or video stream). So I 
don't know why you saw those strange PTS changes (before you did the 
seek)...

-- 

Ross Finlayson
Live Networks, Inc.
http://www.live555.com/