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

Cory Papenfuss papenfuss at juneau.me.vt.edu
Fri May 6 13:35:40 UTC 2005

> After having used Project X for a long time now, and reading of these
> problems, I had a hunch it was the deumxing of the streams initially
> that may be causing the sync issues. After all, remuxing cannot add
> back what is not present in the demuxed streams, and so if the sync is
> not fixed at this stage, I can't see the remuxing magically sorting it
> out.
 	I had pretty much figured out that it was the demux/remux stage in 
almost all of the "MythTV to DVD" scripties and HOWTOs out there that was 
breaking the sync.  After I looked into it, I discovered the that the 
PTS/DTS info is that the ProgramStream level... once it's demuxed into ES 
or PES's, you've screwed the pooch....

... UNLESS it's fixed before it's demuxed.  After playing with ProjectX a 
bit more, I see that at the end of his little parsing, he spits this out:

--> MPEG Audio (0xC0)
Audio PTS: first packet 00:00:00.333, last packet 02:08:19.185
Video PTS: start 1.GOP 00:00:00.400, end last GOP 02:08:21.192
-> adjusting audio at video-timeline
-> src_audio: MPEG-1, Layer2, 48000Hz, stereo, 192kbps, noCRC @ 00:00:00.000
!> 81 frame(s) (1944ms) added @ 02:07:16.992p
audio frames: wri/pre/skip/ins/add 318289/0/0/0/81 @ 02:07:18.936 done...
---> new File: /space/HOME_VIDEOS/Tape5.mpa

summary of created media files:
.Video (m2v):   228939 Frames   02:07:18.930 
Audio 0 (mp2):  318289 Frames   02:07:18.936    0/0/0/81 
=> 4372557132 bytes written...

 	That looks like he added 81 frames of audio (as padding?) to keep 
demuxed sync.  Also, he threw out a bunch of bad B-frames, etc in the .m2v 

> On my 2.4G system, demuxing takes only a few minutes - if its >30
> minutes there could either be significant errors, non standard
> settings in ProjectX, or lots of other disk activity occuring at the
> same time.
 	I'll second that.  It's not *too* slow... I'd say 5-10 minutes on 
a 2-3 gig, 1-hour capture.  That's certainly acceptable if it's scripted.

> Haven't played much with the CLI yet as my video processing is not
> done on my myth box, but this may now soon change if a suitable
> demux/edit/remux combo is found.

 	I haven't convinced myself that a simple byte offset ASCII file is 
sufficient for a cutlist.  If it is, I'd like to try exporting a cutlist 
from mythtv to try GOPCHOPing.


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

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