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

Tue Jan 26 21:28:18 UTC 2010

On Sat, Jan 23, 2010 at 6:55 AM, steve <networks1 at cox.net> wrote:
>>>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 realize this post had hopped threads and I was late replying
to the original post a few minutes back.

So it seems you've got prebuffering pause in your logs. Have you
worked through the solutions on that wiki page yet?

http://www.mythtv.org/wiki/Troubleshooting:Prebuffering_pause

-JohnnyJboss

>>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?
>
>
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