[mythtv-users] mpeg2 video stuttering

[R. G. Newbury]

ojw at weilerfamily.com wrote:
> Quoting "Michael T. Dean" <mtdean at thirdcontact.com>:
> 
>> On 09/23/2008 07:44 PM, ojw at weilerfamily.com wrote:
>>> After having ditched the idea that a 1.8Ghz P4 can display
>>> 1080i content, I invested in a dual core Wolfdale processor
>>> (45nm) at 2.53Ghz and paired it with a Gigabyte GA-73PVM-2SH
>>> motherboard (Nvidia 630i based mobo with a GeForce 7100 built
>>> in).  I'm using two Pinnacle PCTV HD Pro USB capture devices
>>> and am only tuning ATSC based terrestrial transmissions.  Both
>>> mythfrontend and mythbackend are running on the same box.
>>>
>>> The problem I'm having is that when I try to view either a
>>> recorded show or something live'ish (from the ringbuffer),
>>> the view jitters.  What should be obviously smooth scene
>>> pans turns into jerky stutter steps through the scene.
>>>
>>> I was thinking it might be the marginally supported PCTV
>>> HD Pro USB stick but I found that when I transfer the
>>> recorded MPEG file to a PC running windows XP (using
>>> windows media player), the video playback is as smooth
>>> as silk.  I checked the CPU utilization during playback
>>> on my mythtv box using top and found that it's usage doesn't
>>> go over 50%.  I also tried configuring for XvMC which results
>>> in a good cpu usage drop (down to 30%) but the image still
>>> stutters about the same amount.
>>>
>>> I also tried playing the resulting mpegs in mplayer on the
>>> mythtv box.  At first, mplayer told me I didn't have enough
>>> CPU power to play the file so I used the -ao null option to
>>> negate sound.  After I did that, mplayer didn't complain but
>>> it stuttered more than during playback in mythtv.
>>>
>>> I'm not sure where to go from here and was hoping you all
>>> could direct me to further diagnostic efforts.  I'd be
>>> happy to post whatever config information you think would
>>> help diagnose this.  I'll start with the basics:
>>>
>>> Kernel: v2.6.26.3
>>> MythTV: 0.21.20080304-1
>>> NVIDIA: 173.14.12
>>> Using HDMI out at 1920x1080
>> http://www.mythtv.org/wiki/index.php/Troubleshooting:Prebuffering_pause
>>
>> And, if it turns out yours is not on there, but you are suffering from
>> prebuffering pauses, please update the page once you find out the cause.  :)
>>
> 
> The prebuffering pause troubleshooting page above seems to
> suggest that in 100% of the prebuffering pause problems, I
> should see a "NVP: prebuffering pause" in the output of
> mythfrontend.  I restarted mythfrontend with a -v all, then
> played a recorded show.  I then searched through the log
> output by typing "grep -i prebuffering" and found no matches.
> 
> Is it possible that I'm still suffering from prebuffering
> pauses?  If not, what else could I check?
> 
> Looking through the output, I did see many occurances of this:
> 
> Xlib:  extension "XVideo-MotionCompensation" missing on display ":0.0"
> 
> So I suppose if nothing else, I guess I figured out that the
> on-motherboard 7100 doesn't support XvMC
> 

That chipset supports xvmc. Much more likely is that your setup is 
misconfigured.

Are you using the nvidia video driver for your kernel? Livna has 
precompiled kernel-driver combos for fedora and I presume other distros 
have similar repos. Or you can build the driver from the tar available 
at nvidia.

If you are using an xvmc capable driver, is the xorg.conf properly set 
up. See the wiki xvmc page for the magic incantations.

(With the most recent nvidia driver versions, all you actually need is 
the 'driver "nvidia"' line in the Device videocard0 section. The driver 
then pulls in everything it needs. This was NOT the case not too long ago.)

This includes having an etc/X11/XvMCConfig file, with the line 
/usr/lib/libXvMCNVIDIA_dynamic.so.1

With these all set, you should get:

# cat /var/log/Xorg.0.log | grep Motion
(II) Loading extension XVideo-MotionCompensation

# cat /var/log/Xorg.0.log | grep XvMC
(**) NVIDIA(0): Option "XvMCUsesTextures" "True"

There is a small program called xvmcinfo which will confirm that you 
have xvmc set up correctly. I will find my copy of the source and post 
it on the wiki xvmc page. I want to see if I can find out who wrote it 
before I post it...I don't remember where/how I got referred to it.

Finally, does your mythtv setup enable xvmc? Try 'mythfrontend 
--version' in a console. You should see 'using_xvmc' in the output. 
Unless you compiled your own version and omitted that switch, it should 
be there on any precompiled version of myth.


Geoff

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