[mythtv-users] M10K XvMC video stuttering

Michael Carland mcarland at bitsgonewild.net
Sun May 15 00:04:16 UTC 2005


On Apr 18, 2005, at 8:48 PM, Michael Carland wrote:

> On Apr 16, 2005, at 3:50 PM, Michael Carland wrote:
>> With both XvMC’s enabled (or just the VIA one), and deinterlace Bob 
>> (2x framerate), the picture looks great, but there are bursts of 
>> “prebuffering pause”s and “WriteAudio: buffer underrun” messages that 
>> go along with stuttering video.
>>
>> With both XvMC’s disabled, no deinterlace, there are no pauses, no 
>> bad log messages, but there is video tearing.
>>
>> With both XvMC’s disabled, and bob deinterlace, video is shown twice, 
>> split screen, with same picture squished on the top and the bottom, 
>> colors are funny (lots of purples and blues), and the whole screen 
>> flickers solid green. It’s a little noticable.
>
> I'm still having no luck with this, although I may be wrong that it 
> works fine when it is not live tv, it just works much better.
>
> I have put a "-v all" log (it's about 1MB) at 
> http://webpages.charter.net/mcarland/mythfrontend.livetv of startup 
> and watching live tv for a short time. From the log, it appears XV and 
> XvMC are being used. I've also done an strace, and see it opening the 
> XvMC library, since the log complains about not finding the nVidia 
> XvMC library.  I count 1 buffer underrun and 32 prebuffering pauses in 
> a 28 second period.
>
> I've bumped down the bitrate to 3500, and that didn't seem to help.
>
> I've tried two different backends, with the same results, and is the 
> same in .17 and .18. I did a copy over NFS from the backend to the 
> frontend, and saw acceptable throughput. I can't remember exactly how 
> fast it was, but it was better than 4MB/sec over a 100Mb link.
>
> Any suggestions on how to narrow this down further?

For the record, this is solved. I am using the ivtv driver, and VBI 
support is still being worked on. I knew this, but thought since I 
wasn't turning on CC, it wouldn't affect me. Wrong.

Turning off VBI in myth setup resolved all but the most minor bits of 
video stuttering.

-Michael



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