Hi everybody,
I'm trying to get information about an interactive service broadcasted on
TPS and CanalSatellite (in France). The service is broadcasted using a data
carrousel.
My goals are to detect the resets of this service (when the information
contained in the service is renewed, the broadcast is resetted (?) ) and to
survey the PIDs for technical parameters (like throughput, broadcast
incidents, carrousel period,...). I don't want to implement a MediaHighway
or OpenTV player...
I modified the DVB/apps/test/test.c program provided with the driver. I
managed to record the bit flow of the PIDs I'm interested in into files (I
won't get applause for that !).
I need now to decode further all this. I've read things about existing
structures to decode a video or audio flow but I couldn't find anything for
data carrousels. Or what I found did stick to my reality (I found the
'packet start code prefix' (0x000001) in the flow but the next byte was not
a valid StreamId !)
I've just looked a dvbtext (mentionned earlier in this mailing list) to see
how 'they' decode teletext. I've noticed the use of mapping tables and
bitewise operations, but I could not relate these operations to something
clear.
The program contains a lot of 'hard coding' (values like "0x3f7f" or "0x80"
in the lines below :
mag->sub=(unham(data[4],data[5])<<8)|(unham(data[2],data[3])&0x3f7f);
mag->flags=unham(data[2],data[3])&0x80; )
and is not fully explaining why these values and why these operations.
[I hope the developper will see no offense...;-) He probably did not mean
to explain DVB/MPEG2 to me in this file]
I would be more than happy if someone could share his knowledge about the
encoding of such data with me... Or share a few pointers on the info I need
to achieve that...
Thanks in advance,
Karim AMRANI
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