[mythtv-users] More HD stuttering

Chris Trown ctrown at safe-mail.net
Fri Dec 2 12:59:34 EST 2005

Jean Connelly wrote:
> Regarding:
>           The system is a 3.06 GHz P4 running Fedora Core 3.  The video Card
>     is a NVidia 5200FX.  For capture, all I have is a HD3000.  I've checked
>     that DMA is working on all the drives.  I built mythtv from stable
>     source, 0.18.1.  I used the following configure options:
>     --enable-xvmc --enable-opengl-vsync --enable-dvb
>     --dvb-path=/lib/modules/2.6.12- 1.1381_FC3smp/build/include
>     --disable-firewire --disable-joystick --disable-ivtv --enable-proc-opt
>     --disable-xvmc-vld --enable-opengl-vsync
> I have close to an identical system; and I have what is probably 
> equivalent stuttering.  HDTV (live or recorded) is totally unplayable in 
> myth.  I have tried with and without opengl sync.  I can't find the xvmc 
> option in the gui with this myth version to disable xvmc for testing.  
> Recorded 1080i plays badly (with frequent pauses and never with audio 
> sync) in mplayer with xvmc and ffmpeg12mc and plays even worse without 
> xvmc.  I'll try transcoding my latest sample clips to see if they are 
> fine when played back at standard resolutions.
> I've got
> 3.06 GHz P4 (which is a 533Mhz FSB chip)
> 512 MB Ram
> BE7-RAID mobo
> Nvidia 5200FX
> Fedora Core 3
> Night before last's myth svn.  No deinterlacing requested.
> Prebuffer pauses all over the place.
> I think what we really need is an hdtv playback test suite external to 
> myth to get better benchmarks on actual system performance.  From 
> previous posts to the list ("well I got *my* P4 1.4Ghz system to 
> playback hdtv") I think that my system *should* be able to playback hdtv 
> without issue, but perhaps there are some motherboard weaknesses or such 
> that make it impossible.

      After some tinkering, I found out what the problem was.  I think. 
  I was trying to play a 1080i stream on a 720p screen.  What I think 
was happening was that the 1080i stream could not be rendered using XVMC 
to 720p.  It had to me done in software, ie: the CPU.  When I changed 
the display to 1920x1080, XVMC kicked in and the image played nicely, so 
long as it was done by root.  No, I wasn't using xrandr.  I will when I 
get everything going under Core 4.

      This prompted my to "upgrade" to Core 4 so I can get realtime 
priority threads via PAM.  I don't really consider it an upgrade.  My 
experience is that Core 4 has more issues than Core 3.  Case in point, 
try compiling 18.1 stable with GCC4.  But I like the idea of running 
mythfrontend as root more distasteful than the problems.


"Those who would give up essential liberty to purchase a little
temporary safety deserve neither liberty nor safety" -- Benjamin

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