[mythtv-users] Gravely audio -- now with buffer underrun!

[steve]

>>Now that I have playback audio working on my system, I notice there is
terrible audio quality.  This is hard to describe, but it’s 
>>“gravely,” like there are very frequent short drop-outs.  This happens not
>only when I play back via Mythtv, but also when I play 
>>the mpeg via the Totem movie player in Gnome.
>> 
>>To rule out the possibility that the capture device (HDPVR) is defective,
I copied the mpeg file onto a windoze machine and played it, and the 
>>audio sounds fine.  To rule out some problem with the >audio hardware on
the linux box I played a CD, which also sounds fine.
>> 
>>So somehow the problem only occurs when playing the audio from mpeg
files.  Mythtv is configured to use ALSA:front for output (ALSA:default 
>>wouldn’t work).  I don’t know if Totem uses that too.  
>> 
>>I realize this appears not to be a mythtv-specific problem (I also posted
on the fedora list) but I was wondering if any other mythtv users 
>>have had this problem, and if so how they fixed it.
>> 
>>Well I checked the frontend log and found additional information (below). 
This explains the intermittent dropouts of audio.  BTW the 
>>subject should have been “graveley” (though the situation is grave). 
Other posts describe this sound as “crackely” or “stuttering.”
>> 
>>Checking some other posts/wiki entries suggested that pulse audio might be
the problem but when I uninstalled alsa-plugins-pulseaudio 
>>the audio quit altogether, so I reinstalled it.  
>> 
>>Tried “aggressive buffering” option.  No help so I turned it off.
>> 
>>Not sure where to go from here.
>> 
>>Steve
>> 
>>2010-01-22 17:22:02.861 TV: Attempting to change from None to Watching
WatchingPreRecorded
>>2010-01-22 17:22:02.921 TV: StartPlayer(0, Watching WatchingPreRecorded,
main) -- begin
>>2010-01-22 17:22:03.241 AFD: Opened codec 0x3223cc0, id(H264) type(Video)
>>2010-01-22 17:22:03.242 AFD: codec AAC has 2 channels
>>2010-01-22 17:22:03.242 AFD: Opened codec 0x32244b0, id(AAC) type(Audio)
>>2010-01-22 17:22:03.243 Opening audio device 'front'. ch 2(2) sr 48000
>>2010-01-22 17:22:03.244 Opening ALSA audio device 'front'.
>>2010-01-22 17:22:03.324 Mixer unable to find control PCM
>>2010-01-22 17:22:03.324 Mixer unable to find control PCM
>>2010-01-22 17:22:03.324 Mixer unable to find control PCM
>>2010-01-22 17:22:03.324 Mixer unable to find control PCM
>>2010-01-22 17:22:03.325 Mixer unable to find control PCM
>>2010-01-22 17:22:03.325 Mixer unable to find control PCM
>>2010-01-22 17:22:03.325 Mixer unable to find control PCM
>>2010-01-22 17:22:03.325 Mixer unable to find control PCM
>>2010-01-22 17:22:03.325 Mixer unable to find control PCM
>>2010-01-22 17:22:03.940 OSD Theme Dimensions W: 1280 H: 720
>>2010-01-22 17:22:04.694 TV: StartPlayer(0, Watching WatchingPreRecorded,
main) -- end ok
>>2010-01-22 17:22:04.695 TV: Changing from None to Watching
WatchingPreRecorded
>>2010-01-22 17:22:04.695 New DB connection, total: 3
>>2010-01-22 17:22:04.698 Connected to database 'mythconverg' at host:
mythtv
>>2010-01-22 17:22:04.700 Realtime priority would require SUID as root.
>>2010-01-22 17:22:04.701 Video timing method: USleep with busy wait
>>2010-01-22 17:22:04.719 ScreenSaverX11Private: DPMS Deactivated 1
>>2010-01-22 17:22:05.014 WriteAudio: buffer underrun
>>2010-01-22 17:22:06.391 NVP(0): prebuffering pause
>>2010-01-22 17:22:06.419 NVP(0): prebuffering pause
>>2010-01-22 17:22:06.456 NVP(0): prebuffering pause
>>2010-01-22 17:22:06.476 NVP(0): prebuffering pause
>>2010-01-22 17:22:06.528 NVP(0): prebuffering pause
>>2010-01-22 17:22:06.568 NVP(0): prebuffering pause
>>2010-01-22 17:22:06.605 NVP(0): prebuffering pause
>>2010-01-22 17:22:06.647 NVP(0): prebuffering pause
>>2010-01-22 17:22:06.698 NVP(0): prebuffering pause
>>2010-01-22 17:22:06.733 NVP(0): prebuffering pause
>>2010-01-22 17:22:06.772 NVP(0): prebuffering pause
>>[continues like this till I escape playback]
>
>I didn't have this problem, but I got the ALSA:front tip from the myth
how-to (http://www.mythtv.org/wiki/Installing_MythTV_on_Fedora) - 
>see the last line in the guide. It also mentioned changing the mixer
setting to master from PCM. Worth a try - I'm not too experienced 
>with this stuff so I'm grasping. Hopefully someone will have more insight.
>

Thanks for the come-back again, George.  (BTW, people on this list seem to
want us to post replies at the bottom rather than the top, 
so I moved yours in this reply.)

I missed that last line! I made the change to the mixer setting, and it
helped a little, but didn't completely eliminate the audio 
dropouts.  Mythfrontend log now says:

2010-01-23 05:30:57.503 TV: Attempting to change from None to Watching
WatchingPreRecorded
2010-01-23 05:30:57.555 TV: StartPlayer(0, Watching WatchingPreRecorded,
main) -- begin
2010-01-23 05:30:57.734 AFD: Opened codec 0x46026d0, id(H264) type(Video)
2010-01-23 05:30:57.734 AFD: codec AAC has 2 channels
2010-01-23 05:30:57.734 AFD: Opened codec 0x45ffec0, id(AAC) type(Audio)
2010-01-23 05:30:57.736 Opening audio device 'front'. ch 2(2) sr 48000
2010-01-23 05:30:57.736 Opening ALSA audio device 'front'.
2010-01-23 05:30:57.804 Mixer unable to find control PCM
2010-01-23 05:30:57.804 Mixer unable to find control PCM
2010-01-23 05:30:57.947 OSD Theme Dimensions W: 1280 H: 720
2010-01-23 05:30:58.548 TV: StartPlayer(0, Watching WatchingPreRecorded,
main) -- end ok
2010-01-23 05:30:58.549 TV: Changing from None to Watching
WatchingPreRecorded
2010-01-23 05:30:58.550 Realtime priority would require SUID as root.
2010-01-23 05:30:58.552 Video timing method: USleep with busy wait
2010-01-23 05:30:58.573 ScreenSaverX11Private: DPMS Deactivated 1
2010-01-23 05:30:58.629 NVP(0): prebuffering pause
2010-01-23 05:30:58.661 NVP(0): prebuffering pause
2010-01-23 05:30:58.699 NVP(0): prebuffering pause
2010-01-23 05:30:58.736 NVP(0): prebuffering pause
2010-01-23 05:30:58.776 NVP(0): prebuffering pause
[etc.]

So changing the mixer setting to master got rid of 7 attempts to find the
mixer and the WriteAudio buffer underrun.  Still getthing 
the prebufffering pauses and associated dropouts though.

The fact that the defaults won't work indicates that ALSA is not configured
properly, and from what I've read this can easily cause the 
prebuffering pauses.  ALSA is pretty complex tho, and I don't completey
understand what it does, so can't figure out what config changes 
are needed to get it to work work. :-/

Anyone?