[mythtv] Broken AV sync after mythtranscode

Geoffrey Hausheer mythtv0368 at phracturedblue.com
Fri Dec 30 11:27:18 EST 2005

On 12/30/05, Adam Egger wrote:
> I just found one failing file with the following last lines:
> 2005-12-30 11:52:36.610 VID: B #:7 nb: 2 pts: 00:17:03.786 dts: 00:17:03.786
> 2005-12-30 11:52:36.610 Id:0 00:17:03.786 V:1 EXT: 199
> 2005-12-30 11:52:36.610 Found invalid PTS (off by -00:00:31.840) at 13:57:47.094
> 2005-12-30 11:52:36.610 Found invalid PTS (off by -00:00:31.840) at 13:57:47.134
> 2005-12-30 11:52:36.610 Found invalid PTS (off by -00:00:31.840) at 13:57:47.174
> 2005-12-30 11:52:36.610 VID: P #:11 nb: 2 pts: 00:17:03.946 dts: 00:17:03.826
> 2005-12-30 11:52:36.610 Id:0 00:17:03.946 V:0 EXT: 199
> 2005-12-30 11:52:36.610 Deadlock detected.  One buffer is full when
>                 the other is empty!  Aborting
Yes, the negative PTS offset (which means the timestamp went backwards
within your file) is causing issues.  This one may be tricky to fix. 
I'll need probably 6 Megs of video around the problem area. 
Unfortunately there is no easy way to do it.  The issue starts at
around 16 mins, 50sec into the program.  I'd need you to cut the
relevant portion (about 10seconds before to 10secs afterward) and send
it to me.  The problem is that while I can correct the stream by hand,
mythtranscode can't process a stream unless it starts on a frame
boundary, so it won't be easy to tell whether you have the right
portion or not.  I think mplayer will play just about anything though,
so you could possibly use it to see whether you got the right portion.

So what you could do:
figure out approx where the cutpoint should be (if it is a 30 minute
recording, 17/30*total bytes)
use 'tail' to trim the front off the stream.  Watch it in mplayer
(you're looking for it to start around V:50250)
then use 'head' to trim the file down to 6MB (make sure you get past
the point in mplayer where you see large negative offsets)

You could possibly try using mpegcut too, but I'm not familiar with it.

Let me kow if this doesn't make sense.   And I'll try to think of a better way.

no, I haven't added support for '--show-progress'  Though it wouldn't
be too hard.  I'll look into it when I get a chance.

And, I added some code lately to try to do subtitle support, but it
turns out to be mostly wasted effort.  the types of subtitles in DVB
recordings aren't suppported in PS video (which is the only format
mythtranscode can write).  Until I add a TS writer, it'll be nearly
impossible to support subtitles (the only other way is to translate
them into DVD-style subtitles, which is far more work than I'm willing
to do).  So if anyone is waiting on subtitle support, it is likely a
long ways off.

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