Bug 194677 – media-tv/mythtv-0.20.2_p14498: audio buffer underruns if viewing while recordings are in process or when chasing playback on in process recordings

• Product: Gentoo Linux
• Status: RESOLVED INVALID

[Description Ali Asad Lotia 2007-10-04 06:20:17 UTC]

When viewing previously recorded content while other recordings are in process, or chasing playback on a recording, the audio becomes very crackly and the frontend output reports buffer underruns. The problem worsens if the audio becomes more complex (e.g. there is background music and dialog and sound effects like crashes or explosions). However, when playing back while no recordings are in progress, there is no problem. 

I have a combined backend/frontend machine with the following specs:
P4 3.2 Ghz
2 GB RAM
1.6 TB LVM partition composed of 2x750GB and 1x250GB disk dedicated to myth
250GB System Disk on which 4GB are in a swap partition
NVIDIA GeForce 6600
On-board Intel HD audio
3 x HD Homerun tuners
2 x PVR-500 tuners

Kernel 2.6.22-gentoo-r8

Tested with nvidia-drivers 100.14.09 and 100.14.19, both have the same problems.

I am reporting this problem because I was previously able to both chase playback without any audio dropouts and watch a previously recorded program while other recordings were in progress. It is not simply a case of an overtaxed machine. Since system load does not go much higher when I initiate playback while recordings are in progress compared with when no recordings are in progress.

I am very thankful for the wonderful ebuilds that people have provided and would be happy to provide information that can help get to the bottom of this matter.

Reproducible: Always

Steps to Reproduce:
1. Check to make sure that a recording is in progress OR start a recording if one is not in progress
2a. Start playing back a previously completed recording
2b. Start viewing a recording progress
Actual Results:  
The video plays back smoothly, but 30 or so seconds into viewing, the audio starts to skip and drops out for short periods. The mythfrontend logs will indicate buffer underruns.

Expected Results:  
Video playback should be smooth regardless of whether a recording is in progress.

I have a combined backend/frontend machine with the following specs:
P4 3.2 Ghz
2 GB RAM
1.6 TB LVM partition composed of 2x750GB and 1x250GB disk dedicated to myth
250GB System Disk on which 4GB are in a swap partition
NVIDIA GeForce 6600
On-board Intel HD audio
3 x HD Homerun tuners
2 x PVR-500 tuners

Kernel 2.6.22-gentoo-r8

Tested with nvidia-drivers 100.14.09 and 100.14.19, both have the same problems.

[Comment 1 Doug Goldstein (RETIRED) 2007-10-04 13:27:34 UTC]

You basically described a disk IO problem that's specific to your system.

What versions of everything did you have previously where it was working and what did you change?

I can guarantee you it wasn't a recent MythTV change since nothing regarding playback has changed in a while.

[Comment 2 Ali Asad Lotia 2007-10-04 19:51:05 UTC]

(In reply to comment #1)
> You basically described a disk IO problem that's specific to your system.
> 
> What versions of everything did you have previously where it was working and
> what did you change?
> 
> I can guarantee you it wasn't a recent MythTV change since nothing regarding
> playback has changed in a while.
> 

Thanks for the response. The interesting issue is that if I use a different frontend machine to display the same recording while other recordings are in progress, there is no problem with the audio.

As far as changes are concerned, along with updating MythTV, I have also upgraded the kernel, the video card drivers (nvidia-drivers) and various AV codecs that mythtv depends on. 

Oh well, its on to the less obvious sources for tracing the problem.