[mythtv-users] Bad DVB-T picture quality on Nova T-500

[Jeppe Madsen]

Hi,

I've been running a mythtv setup for quite a while, but have always
had mixed results with the quality of the recordings. I'm using a Nova
T-500 dual tuner DVB-t card to record standard SD channels.

The problem I'm seeing is that many recordings have very bad mpeg
artifacts, with high pitching noise etc. I've looked at the logs at
one of the recordings, and I see a lot of this:

2009-04-13 19:38:33.494 [mpeg2video @ 0x2b9400cbf6f0]skipped MB in I frame
at 29 25
2009-04-13 19:38:33.692 [mpeg2video @ 0x2b9400cbf6f0]skipped MB in I frame
at 10 24
2009-04-13 19:38:35.469 [mpeg2video @ 0x2b9400cbf6f0]00 motion_type at 10 15
2009-04-13 19:38:35.696 [mpeg2video @ 0x2b9400cbf6f0]ac-tex damaged at 43 11
2009-04-13 19:38:35.701 [mpeg2video @ 0x2b9400cbf6f0]ac-tex damaged at 37 13
2009-04-13 19:38:35.792 [mpeg2video @ 0x2b9400cbf6f0]00 motion_type at 1 23
2009-04-13 19:38:36.696 [mpeg2video @ 0x2b9400cbf6f0]skipped MB in I frame
at 6 22
2009-04-13 19:38:41.215 [mpeg2video @ 0x2b9400cbf6f0]skipped MB in I frame
at 0 24
2009-04-13 19:38:41.337 [mpeg2video @ 0x2b9400cbf6f0]ac-tex damaged at 34 23
2009-04-13 19:38:41.416 [mpeg2video @ 0x2b9400cbf6f0]skipped MB in I frame
at 24 20
2009-04-13 19:38:41.454 [mpeg2video @ 0x2b9400cbf6f0]invalid mb type in P
Frame at 28 13
2009-04-13 19:38:41.477 [mpeg2video @ 0x2b9400cbf6f0]00 motion_type at 40 19
2009-04-13 19:38:41.495 [mpeg2video @ 0x2b9400cbf6f0]00 motion_type at 43 23
2009-04-13 19:38:41.515 [mpeg2video @ 0x2b9400cbf6f0]ac-tex damaged at 21 18
2009-04-13 19:38:41.544 [mpeg2video @ 0x2b9400cbf6f0]00 motion_type at 3 22


So my questions are:

1) Any idea what's the root cause of this?
2) Is it a signal problem? Sometimes the recordings are flawless,
   sometimes they are all messed up. I think there may be a
   correlation with the weather conditions....
3) Can it be a hw/os system problem? (I'm running this under Xen
   btw). If so, how to diagnose?


Some system info:

mediaserver2:~# uname -a && cat /etc/debian_version &&  mythbackend
--version
Linux mediaserver2 2.6.18-6-xen-amd64 #1 SMP Thu Dec 25 22:21:42 UTC 2008
x86_64 GNU/Linux
4.0
Please include all output in bug reports.
MythTV Version   : Unknown
MythTV Branch    : tags/release-0-21
Library API      : 0.21.20080304-1
Network Protocol : 40
Options compiled in:
 linux profile using_oss using_alsa using_arts using_jack using_backend
using_dbox2 using_dvb using_firewire using_frontend using_hdhomerun
using_iptv using_ivtv usioystick_menu using_libfftw3 using_lirc
using_opengl_vsync using_v4l using_x11 using_xrandr using_xv using_xvmc
using_xvmcw using_xvmc_vld using_bindings_perl using_bngs_python
using_opengl using_ffmpeg_threads using_libavc_5_3 using_live


mediaserver2:~# cat /etc/modprobe.d/options

options dvb_usb disable_rc_polling=1
options dvb-usb-dib0700 force_lna_activation=1 debug=2

rgds
Jeppe
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