[mythtv] DVB subtitles and TS->PES decoder

Marcus Metzler mocm at mocm.de
Fri Nov 26 08:20:16 UTC 2004

>>>>> "Torbjörn" == Torbjörn Jansson <torbjorn.jansson at mbox200.swipnet.se> writes:

    >> AFAIKT the TS to PES conversion uses my routines from the
    >> dvb-mpegtools package. This is good enough for a quick and
    >> dirty transformation, but can not be used for e.g. authoring
    >> DVDs where you have to get the muxing correct and add some more
    >> time stamps. That's why I started dvb-replex (see
    >> http://www.metzlerbros.org/dvb/index.html)

    Torbjörn> A little comment about replex, i have a tt dvb-c card
    Torbjörn> that have some reception problems on certain channels.
    Torbjörn> Sometimes when i record with the dvb card the resulting
    Torbjörn> file somehow gets written corrupted, which casue
    Torbjörn> problems for mythtv.  I have tried to fix the files with
    Torbjörn> replex but it always quits at about the same place as
    Torbjörn> mythtv have problems, replex says something about video
    Torbjörn> ringbuffer overflow and some numbers.  I don't remeber
    Torbjörn> the exact error message.

    Torbjörn> even better fix mythtv so it can handle those
    Torbjörn> problematic files?

    Torbjörn> When this happeds i can play the file with video lan
    Torbjörn> client on my windows computer and it will usualy work
    Torbjörn> prety well, the picture may freeze at the problematic
    Torbjörn> position but i can always fix that by jumping forward a
    Torbjörn> bit in the file.

If you want to fix the file you have to take apart the MPEG stream and
check each frame and if you find a broken frame have some strategy to
fix it. replex right now takes apart the stream and tries to recognize
single frames, tag them with a time stamp and then put the stream back
together. What woud have to be done is not only find trhe frames but
check their integrity and then fix it, i.e. put another layer into the
replex process.
For an MPEG player it is a little easier. The player alread checks or
better has to decode every frame, so it certainly can find a broken
frame. The question is what it does to recover from the error.It could
just ignore it and continue with the next time I-frame, that would
lead to a small freeze in playback or in case of an audio frame to a
sound drop out.


| Dr. Marcus O.C. Metzler        |                                   |
| mocm at metzlerbros.de            | http://www.metzlerbros.de/        |
 |>>>             Quis custodiet ipsos custodies                 <<<|

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