[mythtv-users] DVD recording sync issues with PVR 350

Cory Papenfuss papenfuss at juneau.me.vt.edu
Thu May 5 18:25:43 UTC 2005

>>         Most likely due to changing A/V sync within the MPEG2 stream.
>> It's a known problem without a known (bug-free) solution.
> Cory,
> Is this just a known issue for hardware-MPEG2-card recorded streams,
> or all MPEG2 streams in general? I regularly record DVB and PVR-350
> streams here in the UK, demux them, edit them, and then burn to DVD
> with no issues at all (using Project X (Java) to demux and fix,
> Cuttermaran to edit [uses mplex], and then DVD Hive [uses dvdauthor,
> mplex, and mkisofs] to create ISO images). I sometimes also reencode
> edited MPEG2 streams that have been through the demux/remux process
> into XVID/DIV5 with no A/V sync problems.
 	It's a known problem for *some* hardware-mpeg2-card captures.  It 
doesn't happen all the time... quite infrequently with broadcast/cable 
sources, actually.  It's caused by the card having a glitch in an A or V 
frame and then throwing it away.  It just adjusts the timestampe to 
compensate.  Particularly problematic captures are those from analog tape 
(VHS, 8mm, etc)... tape players typically put out pretty lousy signal 
quality.  The quality isn't normally perceivable, but it could be missing 
some sync info, have the timing off a bit, etc... people don't mind, but 
capture cards have major issues with small timing glitches.

> Does this problem affect all popular linux-based tools mentioned in
> this thread? I use the above tools on my Win2K box because they are
> all GUI-driven and, having not tried other tools and because they
> worked, have not looked at others. It'd sure be good to be able to do
> it all driven from a GUI on my myth box from the sofa!
 	Most linux-based tools use the same backend tools to do the 
processing.  Basically, anything that relies on stripping A and V streams 
apart and then remuxing them will break.  The PTS info is at the PS 
level... once it's been ripped into PES or ES, the sync info is gone. 
Digital broadcasts (like HD or DVB) will most likely be better mastered 
without the varying sync (although not necessarily).

 	Notable programs that definately *are* broken are any scripts that 
strip A/V and remux, or those that use avidemux.  Avidemux cannot deal 
with varying sync.


* Cory Papenfuss                                                        *
* Electrical Engineering candidate Ph.D. graduate student               *
* Virginia Polytechnic Institute and State University                   *

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