[mythtv-users] Current state-of-the-art for h264 cutlist processing?

[John Pilkington]

On 01/02/18 13:10, John Pilkington wrote:
> Hi:  I rarely record DVB-T2 HD h264 recordings in which I want to make 
> internal cuts, but it would be good to be able to do make them in a way 
> that doesn't introduce glitches in playback.
> 
> I find that Mythfrontend does a good job in playing uncut recordings 
> with cutlists, but uPnP then plays all the ads and skipping is painful.
> 
> My MythDVBcut script chops at videokeyframes; there may be glitches at 
> cuts but there's no long-term loss of quality or a/v sync.  I've found 
> other scripts that work similarly and are more elegantly coded. Frontend 
> and uPnP glitches may differ in style and severity.
> 
> I've tried going via mkvmerge but at present see a/v sync drift and 
> haven't found an mkv/audio format that my tv plays acceptably via uPnP
> 
> So, before I waste yet more time, has anyone found (or developed) a 
> toolchain that is available and does this job properly?
> 
> Thanks,
> 

I posted that a few weeks ago.  There hasn't been much comeback, perhaps 
because multi-terabyte disks have become affordable, or perhaps through 
disillusionment, but I do now have a script that works reasonably well 
with UK DVB-T2 HD h264 recordings and might be useful elsewhere.  I have 
appended it to the MythDVBcut entry in the MythTV wiki; I've called it 
MythTScut.

It uses mythffmpeg, with mapping to give one video and one audio stream. 
  That could probably be changed, but I haven't tested any more.  I find 
that it needs two runs, the first with no cutlist, to discard 
unrecognised streams and get the cuts in (about) the right position.  At 
present the most successful commands seem to be:
============
with no cutlist

mythTScut.sh /path/to/infile.ts R 1

mv infile.ts.old ... to somewhere else, say infile_orig.ts

establish editpoints showing wanted keyframes using the frontend editor

mythTScut.sh /path/to/infile.ts R 1
============
The output may be either a Recording (R), replacing the renamed original 
file and clearing its cutlist and bookmarks, or a Video (V) which leaves 
these unchanged. The third parameter (1,2) is intended to define the way 
in which the input streams are synched, but I find that 2 is still 
rather unpredictable or prone to failure.  I have tried several ffmpeg 
options without getting anything that seemed better. YMMV

ffmpeg complains during both passes, which are primarily 
disk-speed-limited.  It still usually works.

Like my earlier scripts, this is intended for use from the desktop, 
giving feedback and creating a logfile that includes the position of the 
cutpoints in the output, and stream details from ffprobe.  The first 
page needs editing to define working directories and database access, 
and intermediate files are not all erased on exit.

I'm posting it as work-in-progress with no guarantees and no implied 
support, in the hope that it may be useful.

 > John P