[mythtv-users] Basic setup problems (XvMC, Lirc, EIT)

Robin Smith 1canuck2 at gmail.com
Sat Jul 26 21:47:33 UTC 2008

> 1. XvMC playback stutters (LiveTV). In Xorg.0.log there is a line
> about using XvMotionCompensation. MythTV configured to use Standard
> XvMC + xvmc-blit or xvmc-opengl. Stutter is worse with -opengl. MythTV
> compiled with "yes" on all the XvMC lines, including -lXvMCNVIDIA.
> With "Standard" decoder and xv-blit playback is smooth without any
> stutter. CPU load in both cases is around 20 % (cpufreq=1 GHz).

The cause of number 1, is likely directly related to Number 6

> 6. Frontend console filled with: "Audio: buffer underrun"

The process of keeping the audio and video in sync is causing the
stuttering and its related. What may be hard to determine is which is
causing which....

Here's the things I did recently to fix my new mythbox.

Dumped PulseAudio and want back to plain old Alsa. Make sure
PulseAudio is not there. Can't explain why as I don't know much about
pulse (its more of a network-based protocol for streaming audio to
other machines, etc), but I'm going to guess you don't need it on your
myth box. IMHO, its not quite ready for primetime yet.

Check out some of the nvidia driver options for xorg. Are you using
the closed source NVidia driver or the OSS one? The closed source one
is "better" performance-wise, even though its closed. Here's the
relevant parts from my xorg.conf (I am using a PCI Express video

Section "Device"
    Identifier     "Videocard0"
    Driver         "nvidia"
    VendorName     "NVIDIA Corporation"
    BusID          "1:0:0"
    BoardName      "GeForce 9600 GT"
    Option         "UseEvents" "true"
    Option         "XvmcUsesTextures" "false"
    Option         "DPI" "100 x 100"
    Option         "PixmapCacheSize" "200000"
    Option         "AddARGBGLXVisuals" "True"
    Option         "NoLogo" "True"

Section "Extensions"
    Option         "Composite" "Disabled"

The lines of most relevance for you to have in xorg are the "Option"
lines. Xorg troubleshooting/tweaking can be a pain in the bum, so make
LOTS of backups.

Backup your /etc/X11/xorg.conf BEFORE doing anything, then you can
copy it back when something breaks (not if, when, cos it will break).
Ideally make changes in little bits, testing along the way (and make
backups when you have a tweak that does not break X.

Check this page out and some of the pages to which it links:

There are also some nvidia driver tweaks you can do using the
nvidia-settings utility, particularly the Sync to v-blank (try it on
try it off. And there's two sync to v-blank check boxes to piddle

You also want to make sure the only AGP stuff running is the nvidia
agp stuff. I found this page when I was tweaking OpenSUSE (its an
Ubuntu page, so I had to adapt some of the steps to OpenSUSE):

Good luck, hope this helps...


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