[mythtv] DVB subtitles and TS->PES decoder

Juha Kuikka juha.kuikka at gmail.com
Thu Nov 25 08:38:58 UTC 2004


I am in the process of writing DVB subtiele parser, it is nowhere near
ready but I looked at how to best integrate it into myth.

First problem I run into is that hte current ts->pes parser in
transform.c does not seem to parse subtitle streams, at least I cannot
get it to output video, audio and subtitle streams, it seems to ignore
the subtitle stream. Does anyone know if this is possible at all or
should I just use my own ts->pes parser and replace the one in
transform.c ?

Concerning this replacement: It seems that DVB TS video stream
contains PES packets that have no size field (it is set to zero). This
is allowed in TS contained PES stream but if we want to store PES
stream in file this has to be corrected. Transform.c:s parser seems to
split these  long PES packets into smaller ones.

I have not yet looked closely at how transfor.c does this but I fear
it is not as simple as cutting the packet info nice pieces and
assembling those into smaller pes packets. One problem might be the
PTS's in the PES headers, I suspect those will have to be correctly
regenerated or it may cause synch problems.

Does anyone have deeper knowledge about this? Spec might be nice?

What is inside these video streams PES packets? Do I have to parse
those too to make the split correctly?

"Easy" solution might be to hack up transform.c to accept more than
two streams but I suspect that is not very easy as the HDTVRecorder
people seem not to have done this.

 - Juha
Juha Kuikka

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