[linux-dvb] Re: GOPs, ts2ps and replex WAS: (Refactored drivers, GOPs, and KaxTV)

[Marcus Metzler <mocm@mocm.de>]

>>>>> "Christophe" == Christophe Thommeret <hftom@free.fr> writes:

    Christophe> Le Mercredi 05 Janvier 2005 09:50, Soyeb Aswat a
    Christophe> écrit :
    >> Hello all,
    >> 
    >> I've recently been finding a problem recording DVB programs
    >> where GOP sections are very large with sometimes many minutes
    >> worth of pictures (they should be only a fraction of a
    >> section).  It doesn't always occur, sometimes the recording is
    >> fine.
    >> 
    >> This problem has been occuring two cards with the refactored
    >> drivers, a Hauppauge Nova-T 90002 and a KWorld DVB-T, and using
    >> the KaxTV version 0.3 (with and without additional patches and
    >> changes).
    >> 
    >> I'm going to investigate this further, but in the meantime I'm
    >> sending this message out to gauge whether anyone else is having
    >> a similar problem.
    >> 
    >> The problem is most noticable with gopchop which, amazingly
    >> enough, tries to chop MPEG-PS files on GOP boundaries.
    >> 
    >> Regards,
    >> 
    >> Soyeb

    Christophe> Hi Soyeb,

    Christophe> Yes, in a well encoded stream, gops typically contain
    Christophe> one iframe.  And i can confirm that on some
    Christophe> channels/providers ts2ps gives huge gops while replex
    Christophe> doesn't. But i don't know if either ts2ps is
    Christophe> responsible of these mad gops or if replex is simply
    Christophe> correcting it.  May Dr. Metzler say more ?

    Christophe> At least, i really doubt that drivers are faulty here.

Neither ts2ps nor replex change anything in the elementary stream,
i.e. GOP or sequence headers. It may be that the program that analyses
the MPEG program stream expects GOP headers to be at the beginning of
PES payloads. Since replex analyses the stream and starts a new PES
for every frame (including setting PTS and DTS) the GOP headers always
occur at the beginning of PES payloads. ts2ps only looks for the start
of a PES in the TS and hacks it into smaller parts (especially video
PES whose length is not restricted in TSs). 
But neither the drivers nor any of my appliactions change anything on
the GOP or sequence header level.

Marcus


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