[linux-dvb] Technicalities of channel searching

["[iso-8859-2] František Boček" <bocekf@iol.cz>]

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> Hello,
> 
> I am slightly confused over what tuning information is _required_ for the 
> DVB-S card to receive a channel, and would be grateful for some 
> clarification.  (The background to these questions is my search for "feeds", 
> for which not all of the tuning information is always known).
> 
> From what I understand, the frequency, polarity, symbol rate and fec give you 
> access to a transport stream, which is split into small (188 byte) packets 
> identified by their PIDs.  The Siemens card seems to auto-detect the fec - is 
> it possible to auto-detect the symbol rate, or do you have to test various 
> symbol rates "manually"?  The latter seems to be the way that "pscan" works.
> 
> However, when searching for feeds (e.g. at 31.5W, 10967V, sr 5632, vpid 308, 
> apid 256 - 1.1m dish in London), pscan-0.5 doesn't find a PMT in the stream - 
> but I can tune into a clear signal using VDR.  How would I go about 
> automatically searching for such transmissions?
> 
I also try to receive/find feeds.  
I think that you can try to find unknown pids  by setting up  demux PES filters for each PID value.
That means you start with PID=1, you set up the filter so the output goes to PC memory, then  you
check whether data are comming from the demux. You can guess if the data are video/audio by checking
the bitrate. Then you try PID=2, 3 and so on.
Note that it's only an idea and I did not check it if it could really work. Also at this moment I don't have an idea how long
does it takes to create a filter+receive some data from it. 

Regards,
Frantisek





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