[mythtv-users] Audio buffer underruns

Victor Brunini victorbrunini at gmail.com
Mon Aug 25 03:14:27 UTC 2014


On Sat, Aug 23, 2014 at 10:03 AM, Victor Brunini <victorbrunini at gmail.com>
wrote:

> On Sat, Aug 23, 2014 at 3:08 AM, Jean-Yves Avenard <jyavenard at gmail.com>
> wrote:
>
>> Hi
>>
>> Le samedi 23 août 2014, Victor Brunini <victorbrunini at gmail.com> a
>> écrit :
>>
>> Hi all,
>>>
>>> I have a combined backend/frontend system that I've been using without
>>> any issues for ~1 year now. Starting in the middle of this week I am
>>> suddenly getting constant audio buffer underruns when trying to play any
>>> video in mythtv. Thus far I have tried/tested:
>>>
>>> 1) Set /proc/asound/card0/pcm1p/sub0/prealloc to it's maximum value of
>>> 32768.
>>> 2) Tried both AC3 passthrough and standard PCM output in mythtv without
>>> success. With PCM the audio is constantly stuttering. With AC3 passthrough
>>> I get a brief (~1s) period of sound and after that see the receiver
>>> constantly switching in and out of Dolby Digital mode due to the buffer
>>> underruns.
>>> 3) Confirmed that mplayer and VLC both play the same video files with
>>> either PCM or AC3 passthrough without any issues.
>>> 4) Confirmed that if I set the mythtv audio output device to NULL video
>>> playback is very smooth and CPU usage is minimal (I'm using VDPAU for video
>>> decoding).
>>> 5) Tried updating to the latest v0.27.3-152-g926bb8d fixes version
>>> available on the mythbuntu repositories (prior to the issues I had disabled
>>> automatic updates).
>>>
>>> A section of the log file generated running with -v audio is available
>>> at http://pastebin.com/J5wZgTYN
>>>
>>
>> Problem is that you've cut your log too much... As a rule of thumb, when
>> reporting a playback problem: never strip your code! As I'm guessing if you
>> knew what to look for in the log, you wouldn't be asking on how to solve
>> your problem here...
>>
>> What's your video card and what playback profile are you using?
>> Change to VDPAU Normal
>>
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>
>
> Hi,
>
> Here's the full pastebin for the log from starting mythfrontend to closing
> mythfrontend: http://pastebin.com/bVqmLcpG
>
> Video card is a GeForce 8400 GS, and I am using VDPAU Normal. I have also
> tried VDPAU Slim and Slim. Those two appear to make it very slightly
> farther (~2 seconds instead of ~1) into the recording before the buffer
> underruns happen.
>
> Thanks,
> Victor
>
>
>
>
Hi,

I've been doing a bit more research and found this old thread that appears
to be similar to the issue that I'm seeing:
http://ubuntuforums.org/showthread.php?t=1632963

In particular I noticed that I am seeing the same issue where mythtv is
detecting a different buffer size and period size than mplayer (which plays
successfully) does. As you can see in the log on pastebin myth is detecting
"ALSA: Buffer size = 24000 | Period size = 6000".

Running mplayer on the same file detects a buffersize of 96000 and a period
size of 1500. The full mplayer output log is available at
pastebin.com/jGCrRRge

Any suggestions?

Thanks,
Victor
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