[vdr] Understanding AC-3

Rob Davis rob at davis-family.info
Thu Sep 2 15:21:56 CEST 2010


Hi Guy's,

How do you go about understanding AC-3 within a VDR context?
(apart from reading up on it online - which now has my head spinning).

I have a Hauppauge PVR-HD and two ATSC cards.  The ATSC cards work as 
they should and with the new atsc/dn patch on 1.7.15 now have the 
correct dpids.

However, if I turn on add new transponders or update pids, then my 
Hauppauge PVR channels lose their dpid values..

Sep  1 19:10:33 oac vdr: [8186] changing pids of channel 920 from 
4113+4097=27:0;4352=eng at 106:0:0 to 4113+4097=27:0:0:0

If I keep automatic channel updates off, then xineliboutput and 
streamdev work for these channels, but vdr-vnsi (xbmc) and vdr-xine 
don't (no audio)..

I'm assuming vdr parses the ac3 headers in some way and sends 
information onto the playback frontend.  How would I go about seeing 
what those headers might be and looking into patching pat.c accordingly?

I noticed all the comments about e-ac3 and wonder if a similar patch 
should be made for this device.

As an aside, vdr recordings from these channels play back fine in vdr-xine.

So, more specifically, I suppose I would like to know how to find out 
the STREAMTYPE:

I'm pretty sure it falls under this:

               case 6: // STREAMTYPE_13818_PES_PRIVATE


But I'd be interested in seeing the flow through this section of pat.c 
and what is happening.. Mainly to see if something needs to be forced on?

I can create a five second VDR recording if someone wants to see what 
the TS stream looks like.. But I'd be interested in diagnosing it myself..

Thanks.

-- 

Rob Davis



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