[mythtv-users] Years of stuttering - prebuffering pauses and now waiting for video buffers

Alex Masidlover amasidlover at alex-masidlover.co.uk
Sun Jun 19 20:31:07 UTC 2011


I have been running MythTV as our PVR for a number of years; I started 
with a combined standard TV backend/frontend and it was OK but suffered 
from occasional stuttering while recording and watching at the same 
time. I then split the backend and frontend and moved to UK DVB-T 
capture cards, I think in the process I started to see stuttering again. 
I then upgraded the backend to be an intel E2140 Core machine (which I 
think cured most of the stuttering). Sometime later I moved to a 1080p 
LCD TV and then later upgraded the frontend to a Core2 machine (mainly 
to try and build a fanless machine).

The system used to get:

2010-11-29 21:23:55.189 NVP(2): prebuffering pause

2010-11-29 21:23:55.691 
RingBuf(myth:// Waited 1.0 
seconds for data to become available...

in the mythfrontend log.

Recently however, the stuttering has become really quite annoying - I 
emailed this list some time ago but got no responses I thought I'd try 
again with more information...

I've tried upgrading mythtv to latest 0.24 and now get the same effect, 
but the messages have changed:

2011-06-19 20:24:41.679 Player(0): Waited 100ms for video buffers 

2011-06-19 20:24:43.113 
RingBuf(myth:// Waited 0.2 
seconds for data
             to become available... 0 < 32768

It does seem that certain TV channels suffer more than others Channel 5 
seems to suffer from a stuttering incident maybe every half hour, but 
the BBC gets them every couple of minutes.

I have tried using custom profiles (VDPAU with max buffers increased and 
ffmpeg + VDPAU).

I moved the myth directory from a USB2 external HDD to a SATA HDD to see 
if that would help and it made no difference.

I changed the myth partition from ext3 to ext2.

I have been through the prebuffering pause guide on the wiki.

I have been through the VDPAU guide(s) on the wiki.

The load average on the frontend is almost always under 0.1 and on the 
backend varies from about 0.2 up to 2.0 (but the stuttering seems not to 
correlate with high load on the backend). The backend does dnsmasq and 
occasional webserving duties - it also does Asterisk, but the stuttering 
seemed not to get any worse or better whether asterisk was running or 

The specs of the machines are:

Frontend: Asus P5N7A-VM Motherboard, 2GB RAM, E5200  @ 2.50GHz, NVIDIA 
GeForce 9300 (onboard) using HDMI output and Realtek ALC1200 onboard 
sound (co-ax digital out).

Backend: Asus P5PE-VM Motherboard, 1GB RAM, E2140 Dual Core CPU @ 
1.6GHz, the OS is Gentoo and is on a PATA drive while the myth drive is 
a SATA drive.

They are connected with 100-BaseTX networking with 2x 'dumb' switches in 
between them.

I'm currently using the gentoo mythtv overlay package 

So, I need to do something with the frontend anyway as I haven't managed 
to make it silent and I'm also looking at changing to DVB-S tuners - 
however, I don't feel like investing much more in the current solution 
if I can't cure the stuttering.

So I have 3 questions:

1) Can I accurately diagnose the cause of the stuttering somehow?

2) If I can't then what upgrades/changes would make most sense to try 
and cure it?

3) Does anyone have a fully working separate backend/fronted system with 
multiple DVB-S or DVB-T tuners that has a silent frontend and doesn't 
stutter - if so can they let me know the configuration of it?



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