[mythtv] mythtranscode MPEG2->MPEG2 issues

[Paul Koster]

Based on some recent threads (e.g.
http://www.gossamer-threads.com/perl/mailarc/gforum.cgi?post=102099;search_string=;guest=2272713&t=search_engine#102099 )
I decided to dive a bit into mythtranscode to transcode from MPEG2->MPEG2 .

First of all I made a bunch of fixes related to the handling of (wrong)
input parameters. I'll make up a patch in a few days for this.

Second, I did a number of tests transcoding a number of recordings without
cutlists and one transcoding with cutlist. The results:
- 4 files completed the transcoding without any problems (for details see
below)
- 1 file failed the transcoding because it encountered a block type of 0xba
indicating a pack header
- 2 files failed the transcoding because mythtranscode encountered a block
type of 0xf4 (I've not been able to find out what kind of object this is)

For one of the files that completed the initial transcoding successfullly I
repeated it with a cutlist (cutting of the end of a show) and tested the
resulting file in a number of players:
- it seems that the cutlist works okay, except that the last (few) frame(s)
are still in there just at the end of the resulting file
- the resulting file plays okay in the internal MythTV 'watch recording'
option without noticable problems
- the resulting file suffers from many artifacts at certain points
(unrelated to the cutpoints ) when playing in Windows Media Player with the
Elegard MPEG2 decoder (compared to the original)
- the resulting file suffers from minor artifacts at certain points
(unrelated to the cutpoints ) when playing in PowerDVD (compared to the
original)

For the 3 files that failed:
- the loop in mythtrans.cpp can't handle unknown object types and will get
into an endless loop because it does not increase framelen, etc.
- I tried to include support for type 0xba, but it seems that just skipping
12 (or 16?) bytes in the stream does not solve the problem as I've seen in
comparable demuxers. I'll try to get a hand on some decent documentation to
see if my PVR 250 outputs valid streams anyway.
- should program streams work or is it just luck that they worked and is the
current code still aimed at transport streams (as mentioned somewhere in a
very old thread)?

All recordings were made with my PVR 250 ivtv 0.19 576x576 MPEG2 Program
Stream 5000 kbps video, 384 kbps audio (mp2). To do the transcoding I used
mythtranscode -i filename.nuv .

Are more people working on this issue beside Geoff (who has no time until
march I read)? It would be so nice to have this feature working :)

--
Paul