[mythtv-users] NVP: prebuffering pause -- what does it mean, really?

Willy Boyd willyboyd at gmail.com
Fri Mar 16 17:44:32 UTC 2007

I'm just looking to understand this one.  At first I was going to post
this to the -dev list, but figured I'd start here.  I'm hoping to get
a better understanding of what the NVP: prebuffering pause message
really means.

Through trial and error, and lots of searching, I've reduced my issue
significantly.  What started as video freezing very frequently,
accompanied by prebuffering pause and "WriteAudio: buffer underrun"
messages, is now only happening sometimes once per couple hours.  VERY
hard to debug, as you can imagine.  I can watch LiveTV or recordings,
sometimes for a couple hours now, across program changes even, and
think "I finally fixed it!".  Then the video will freeze.  I check
mythfrontend's log, and I see "NVP: prebuffering pause", followed by
"NVP: Prebuffer wait timed out 10 times.", repeated ad finitum until I
restart the frontend.  This is on SD only, recorded over svideo on a

I've posted before on this issue, but I got quiet once I got it
reduced to happening so rarely.  I'd really like to understand what's
going on though to try and squash it entirely.  I miss the days when
I'd turn the tv on, see that someone left LiveTV mode on overnight,
and it's still playing flawlessly!  Not a great thing to do, but still

I have done this so far:

- disabled GLX and GL in frontend settings, in case it was an NVIDIA/GLX problem
- turned on "extra audio buffering", this greatly reduced the
WriteAudio messages
- disabled "aggressive audio buffering", as this didn't help (might
have made it worse)
- added "enc_mpg_buffers=16" to my ivtv module settings
- got right configure settings for SVN (at first I was missing MMX support)
- tried two different soundcards (same vers of ALSA, tho)

I've posted about this before, but here's my setup:

Fedora Core 6 -- 2.6.19-1.2911.6.5.fc6
ASUS M2NPV-VM w/ NVIDIA 6150, using VGA @ 1360x768
  - bios 0303 I think
  - nvidia 9746 driver
AMD 3800+ AM2
1GB DDR800
1 x PVR-250
  - ivtv 0.10.1
Turtle Beach Audio Advantage Micro
  - snd_usb_audio from alsa 1.0.13
  - OR, onboard Intel HD Audio with snd-hda-intel from same alsa version
MYTH (combined be/fe): 0.20.20070124-1, rev13016

*whew*  I think that covers it.  Please ask me if I missed something.
I think the M2NPV-VM is a quite popular setup, so I'm confident I can
get this figured out and REALLY want to.  I'm worried about what it
would take to rollback to ivtv 0.7.0 because that means kernel 2.6.17
and other driver support needed, but that might be my next step.  I
lost track of my db backups so I don't think I can really go back to
0.20 or 0.20-fixes, either.

Please help out if you have ideas whatsoever, or a basic knowledge of
what "prebuffering pause" means.  Is the video stream too slow?  Held
up waiting for slow audio?  Can I increase buffers elsewhere?

- Willy

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