[mythtv-users] How do you "tune" subchannels in QAM?

Marc Tousignant drayson at net1plus.com
Fri Apr 1 01:55:43 UTC 2005

>Have you been able to successfully tune the frequencies using azap? (get 
>the instructions for installing it here: 
>You might try just getting your card to successfully tune the channels, 
>and as a worst case scenario, use the frequencies reported by azap for 
>your channels in the DVB Transports section of the MythTV configuration.
>But first, just to rule out problems with your driver setup, you need to 
>make sure azap works.


Azap works to tune channels and Dvbscan confirms there are subchannels

yggdrasil root # azap -c /root/channels.conf-qam-correct -r c82
using '/dev/dvb/adapter0/frontend0' and '/dev/dvb/adapter0/demux0'
tuning to 573000000 Hz
video pid 0x0000, audio pid 0x0000
status 1f | signal 0977 | snr fded | ber 00000000 | unc 00000000 |
status 1f | signal 0977 | snr fdd5 | ber 00000000 | unc 00000000 |
status 1f | signal 0977 | snr fded | ber 00000000 | unc 00000000 |

yggdrasil root # dvbscan -cvvv
using '/dev/dvb/adapter0/frontend0' and '/dev/dvb/adapter0/demux0'
parse_section:981: pid 0x00 tid 0x00 table_id_ext 0x80b6, 0/0 (version 2)
parse_section:981: pid 0x30 tid 0x02 table_id_ext 0x0001, 0/0 (version 4)
PMT 0x0030 for service 0x0001
  VIDEO     : PID 0x0800
  OTHER     : PID 0x0801 TYPE 0x81
  OTHER     : PID 0x0802 TYPE 0x81
parse_pmt:798: 0x0000 0x0001: (null) -- (null), pmt_pid 0x0030, vpid 0x0800,
apid 0x0000 ()
parse_section:981: pid 0x31 tid 0x02 table_id_ext 0x0002, 0/0 (version 26)
PMT 0x0031 for service 0x0002
  VIDEO     : PID 0x0840
  OTHER     : PID 0x0841 TYPE 0x81
parse_pmt:798: 0x0000 0x0002: (null) -- (null), pmt_pid 0x0031, vpid 0x0840,
apid 0x0000 ()
WARNING: filter timeout pid 0x0011
dumping lists (2 services)
[0001]                   (0x0001) 00: PCR == V   V 0x0800
[0002]                   (0x0002) 00: PCR == V   V 0x0840

Dvbstream broadcasts the TS over the network so I can watch it live with
yggdrasil root # ./dvbstream/dvbstream -v -qam 256 -f 573000000 -c 0 8192
dvbstream v0.6 - (C) Dave Chapman 2001-2004
Released under the GPL.
Latest version available from http://www.linuxstb.org/
Tuning to 573000000 Hz
Using DVB card "pcHDTV HD3000 HDTV", freq=573000000
tuning ATSC to 573000000, modulation=5
Getting frontend status
Bit error rate: 0
Signal strength: 916
SNR: 64981
UNC: 0
dvbstream will stop after -1 seconds (71582788 minutes)
Streaming 1 stream

>You shouldn't have to do this! Please make sure your card is configured 
>correctly.. (see my previous post) Channel scanning should work just 
>fine, and put all of the appropriate entries in your channels lineup. If 
>it doesn't, something else is probably wrong.

It's the only way I can get myth to agree with me that there is something
coming in on my card.
The channel scan myth performs locks on all the right channels but reports
timed out while tuning.

You got any better ideas I'm open to trying.

Got home and tried the channel I setup. It plays.. Kinda.. it's almost as if
something within mythtv itself is interfering with the signal or hampering
playback. I get massive pixelization and the audio skips so much you can't
hear anything understandable.

Feeding from dvbstream to videolan works flawlessly through my network.
Both my myth system (yggdrasil) and my gaming system (nidheg) are P4
3.40GHz's with GeForce FX 5700LE's
The key differences between them are; nidheg has an audigy card and 1 gig
ram and yggdrasil has the capture cards, PVR-350 and HD3000, and 512 meg
Ya overkill but yggdrasil is intended to be front/back and a transcoder with
all intentions of lasting a long time.


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