[pvrusb2] Audio problem: DC offset?

[Jan Ceuleers]

Dear list,

I have an occasional problem whereby "an event" occurs following which
all recordings made using the affected tuner have no usable audio.

Tuner: HVR1900.

"Event": no clue. All recordings made using MythTV.

Audio symptoms: affected recordings, when starting or stopping playback
(at any location within the recording) produce a loud popping noise
followed by silence.

So in more detail:

- press Play: <POP> video starts, no audio
- press Pause: <POP> video freezes
- press Play again: <POP> video resumes, no audio
- press Fast Forward: <POP> video fast-forwards
- press Play: <POP> video resumes at normal speed, no audio
- press Stop: <POP>

If this were an analogue system I'd suspect that audio is being recorded
with a large DC offset that saturates the amp; does that ring any bells?

What fixes it (for subsequent recordings) is unloading and reloading the
pvrusb2 module, like so:

====
#!/bin/bash
/sbin/stop mythtv-backend
/sbin/rmmod pvrusb2
/bin/sleep 5s
/sbin/modprobe pvrusb2

while true
do
  [ -h /dev/videop0 ] && [ -h /dev/videop1 ] && [ -h /dev/videop2 ] && [
-h /dev/videop3 ] && break
  /bin/sleep 5s
done

/sbin/start mythtv-backend
====

(As you can see I have 4 tuners, and after reloading the module I have
to wait for udev to recreate the persistent links to the tuners before
restarting the Myth backend).

I have found and am using the "IVTV audio fix" [1] in my channel change
script; this does not prevent the problem.

[1]: http://www.mythtv.org/pipermail/mythtv-users/2014-May/363737.html

This problem does not happen very often. When it does I'm afraid I
rapidly delete the recording in hopes of catching a rerun. So I
currently don't have one to share. If it helps I will resist rapidly
deleting the next occurrence.

Version info:

root at zotac:~# lsb_release -a
No LSB modules are available.
Distributor ID:	Ubuntu
Description:	Ubuntu 12.04.4 LTS
Release:	12.04
Codename:	precise
root at zotac:~# uname -a
Linux zotac 3.11.0-23-generic #40~precise1-Ubuntu SMP Wed Jun 4 22:06:36
UTC 2014 x86_64 x86_64 x86_64 GNU/Linux
root at zotac:~# mythbackend --version
Please attach all output as a file in bug reports.
MythTV Version : v0.27.1-15-g050bf9d
MythTV Branch : fixes/0.27
Network Protocol : 77
Library API : 0.27.20140520-1
QT Version : 4.8.1
Options compiled in:
 linux profile use_hidesyms using_alsa using_oss using_pulse
using_pulseoutput using_backend using_bindings_perl
using_bindings_python using_bindings_php using_crystalhd using_dvb
using_firewire using_frontend using_hdhomerun using_ceton using_hdpvr
using_ivtv using_joystick_menu using_libcec using_libcrypto
using_libdns_sd using_libfftw3 using_libxml2 using_lirc using_mheg
using_opengl using_opengl_video using_qtwebkit using_qtscript
using_qtdbus using_sdl using_taglib using_v4l2 using_x11 using_xrandr
using_xv using_profiletype using_bindings_perl using_bindings_python
using_bindings_php using_mythtranscode using_opengl using_vaapi
using_vdpau using_ffmpeg_threads using_mheg using_libass using_libxml2


Any hints would be greatly appreciated.

Thx, Jan