[mythtv-users] Lossless Transcode 0.25

[Scott & Nicole Harris]

>> As far as the other suggestion, it's a bit above my paygrade, so I'll 
>> have to look into how to dothat.  Do you mean multiplex one of the "bad" 
>> recordings?

>It's not at all difficult.  All three of those have some form of GUI
>available.  Just add one of the bad files into the source list in the
>GUI, and hit run.  All it's going to do is take those raw codec streams
>and stuff them into a different container type.  Think of it like
>extracting files from a ZIP archive and putting them in a tarball.  Your
>recordings start as an MPEG TS container, and the lossless transcoder
>outputs an MPEG PS container.  I'm curious as to whether the new bits of
>video are actually damaged, or if something strange is going on with the
>container that is giving MythTV troubles.

OK, here's what we got.  I tried playing a post transcode damaged file with 
VLC (on Ubuntu and Windows).  Where in Myth playback, there would be a 1 
second flash of purple lines, in VLC, it just stuttered all over itself at 
those points.  More accurately, in Myth playback playcback is [fade to 
commercial] -> [purple bars where lossless transcode took the commercial 
out] -> [show picks up at cut point].  In VLC, it was [fade to 
commerical] -> [5 - 6 seconds of black screen] -> [3 or 4 seconds of 
stuttering audio and video before finally "catching" itself about 10 seconds 
into the next scene of the show].

I then used mkvtoolnix and multiplexed it as requested.  When I played that 
file back in VLC, it displayed the purple lines like Myth playback does.

mkvtoolnix als had some warnings while doing its thing....

Warning: Found one or more B frames without second reference in the first 
GOP. You may want to fix the MPEG2 video stream or use smart reencode before 
attempting to multiplex it.
Warning: Shortened GOP detected. Some frames have been dropped. You may want 
to fix the MPEG2 video stream before attempting to multiplex it.
Warning: Shortened GOP detected. Some frames have been dropped. You may want 
to fix the MPEG2 video stream before attempting to multiplex it.
Warning: Shortened GOP detected. Some frames have been dropped. You may want 
to fix the MPEG2 video stream before attempting to multiplex it.
Warning: Shortened GOP detected. Some frames have been dropped. You may want 
to fix the MPEG2 video stream before attempting to multiplex it.
Warning: Shortened GOP detected. Some frames have been dropped. You may want 
to fix the MPEG2 video stream before attempting to multiplex it.
Warning: '/mythtv_storage2/recordings/1031_20120319213100.mpg' track 1: This 
AC3 track contains 1442 bytes of non-AC3 data which were skipped. The 
audio/video synchronization may have been lost.
Warning: Shortened GOP detected. Some frames have been dropped. You may want 
to fix the MPEG2 video stream before attempting to multiplex it.
Warning: Shortened GOP detected. Some frames have been dropped. You may want 
to fix the MPEG2 video stream before attempting to multiplex it.
Warning: Shortened GOP detected. Some frames have been dropped. You may want 
to fix the MPEG2 video stream before attempting to multiplex it.
Warning: Shortened GOP detected. Some frames have been dropped. You may want 
to fix the MPEG2 video stream before attempting to multiplex it.
Warning: Shortened GOP detected. Some frames have been dropped. You may want 
to fix the MPEG2 video stream before attempting to multiplex it.
Warning: Shortened GOP detected. Some frames have been dropped. You may want 
to fix the MPEG2 video stream before attempting to multiplex it.
Warning: Shortened GOP detected. Some frames have been dropped. You may want 
to fix the MPEG2 video stream before attempting to multiplex it.
Warning: Video ended with a shortened group of pictures. Some frames have 
been dropped. You may want to fix the MPEG2 video stream before attempting 
to multiplex it.

Now, one other thing I've noticed.  The purple lines every 50 seconds is not 
as consistent as the purple lines at every removed cutpoint (which is 100% 
of the time) across recordings.   Some files have no 50 second purple and 
some have it every 50 seconds, and it SEEMS (I can't 100% confirm this yet) 
that 720p recordings have it every 50 seconds and 1080i recordings do not; 
again both have them 100% of the time at removed cut points.