[mythtv] Error: Wrong PMT and Failed CRC check after UK freeview network changes

Roger James roger at beardandsandals.co.uk
Tue Nov 24 12:20:31 UTC 2009

After the recent DVB transmission network changes here if the north west 
of England my rescanning of transports on mythtv 0.21 installation 
seemed to have worked OK (after a few hiccups involving the the 
transport scan picking up frequencies from the main transmitter not the 
relays out of the NIT). However after a while I noticed that one channel 
was not picking  up EIT(EPG) information. This channel was BBC2, 
serviceid 4287 on transportid 4168. Other channels on the same transport 
appeared to getting updated guide data fine.

I turned on eit and siparser logging and noticed the following errors 
being logged when I switched live tv to the BBC2 channel (which viewed 

2009-11-23 17:44:42.324 PESPacket: Failed CRC check 0x76174442 != 
0xc3bfa4b5 for StreamID = 0x70
2009-11-23 17:44:43.322 PESPacket: Failed CRC check 0x76174443 != 
0xc3bfa4b5 for StreamID = 0x70
2009-11-23 17:44:44.327 PESPacket: Failed CRC check 0x76174444 != 
0xc3bfa4b5 for StreamID = 0x70
2009-11-23 17:44:45.323 PESPacket: Failed CRC check 0x76174445 != 
0xc3bfa4b5 for StreamID = 0x70
2009-11-23 17:44:46.323 PESPacket: Failed CRC check 0x76174446 != 
0xc3bfa4b5 for StreamID = 0x70
2009-11-23 17:44:47.328 PESPacket: Failed CRC check 0x76174447 != 
0xc3bfa4b5 for StreamID = 0x70
2009-11-23 17:44:48.325 PESPacket: Failed CRC check 0x76174448 != 
0xc3bfa4b5 for StreamID = 0x70
2009-11-23 17:44:49.313 PESPacket: Failed CRC check 0x76174449 != 
0xc3bfa4b5 for StreamID = 0x70
2009-11-23 17:44:50.327 PESPacket: Failed CRC check 0x76174450 != 
0xc3bfa4b5 for StreamID = 0x70
2009-11-23 17:44:51.324 PESPacket: Failed CRC check 0x76174451 != 
0xc3bfa4b5 for StreamID = 0x70
2009-11-23 17:44:53.715 DTVSM(201) Error: Wrong PMT; pmt->pn(6016) 
2009-11-23 17:44:53.721 DTVSM(201) Error: Wrong PMT; pmt->pn(4544) 
2009-11-23 17:44:53.722 DTVSM(201) Error: Wrong PMT; pmt->pn(4288) 
2009-11-23 17:44:53.723 DTVSM(201) Error: Wrong PMT; pmt->pn(4608) 
2009-11-23 17:44:53.724 DTVSM(201) Error: Wrong PMT; pmt->pn(4672) 
2009-11-23 17:44:53.726 DTVSM(201) Error: Wrong PMT; pmt->pn(4352) 
2009-11-23 17:44:53.727 DTVSM(201) Error: Wrong PMT; pmt->pn(4736) 
2009-11-23 17:44:53.728 DTVSM(201) Error: Wrong PMT; pmt->pn(4168) 

I then used dvbsnoop to look at the PAT and PMT. The PAT showed that the 
PMT for 4287 was being transmitted on PID 200 and the snoop for this PID 
produced a correctly formatted PMT with the correct program number (4287).

I then noticed that I never saw a PAT for the correct transport (4168) 
being built, other numerous other ones were. My suspicion is that 
somehow an old PAT is being used although a quick glance through the 
database did not produce any obvious candidates for where it might be 
stored.  So my first question is. Does myth cache PATs and if so where? 
If it doesn't then how does it determine which PMT pids to look at?

Also I wonder if the CRC errors are something to do with this as they 
occur immediately before the Wrong PMT errors are logged.

I do not want to upgrade to 0.22 (it does not seem to be available on 
debian.multimedia yet) before I have bottomed this out.

Any ideas anyone?



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