[mythtv-users] Audio gone 'helium'

Ben Buxton mythtv at ml.cactii.net
Wed Jun 29 10:17:51 UTC 2005

I've been running my mythbox for some months now, using the following

- PVR250
- Skystar2 DVB
- CMEDIA audio out (SPDIF), alsa driver
- Nvidia MX440 Svideo out, nvidias own driver

Until a couple of days ago, everything worked brilliantly...perfect
smooth picture and crystal clear audio, for both recordings and live tv.

However, all of a sudden yesterday, both livetv and playback have been
very strange, with things seemingly shifted up a pitch and up a gear.
People sound like they're breathing helium and everything runs a
fraction faster. To my knowledge, I've not made any changes to the
system. I have determined the following.

It's _not_ time scaled...the osd shows everything running at 1.0x.

If I disable Video sync timing (i've been using opengl vsync), then
everything comes back to normal speed. So it seems to be related to
this. I want to turn my vsync timing back on though!

Normal video through mplayer (also playing the .nuv files) is perfect.

I tried two different nvidia driver versions for the X display and the
problem persists. I tried rebooting - problem persists. Tried a complete
power cycle, and the problem persists.

My refresh rate should be fine - I'm running it at 50Hz (PAL) and this
hasn't changed.

One clue is that the frontend shows 'audio buffer underrun' on the

Anyone have any ideas where I should look next?


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