[mythtv-users] XvMC and OSD

Robert Johnston anaerin at gmail.com
Tue Apr 5 22:56:30 UTC 2005


On Apr 5, 2005 4:44 PM, Alan Hagge <ahagge at wbfa.com> wrote:
> I had a similar question:  I'm on an Athlon XP 1700+ (o/c ed to 2000+),
> and HD content plays back smoothly (finally) using XvMC, but not Xv.
> However, even with XvMC, playback gets jumpy and I see "prebuffering
> pause" messages if the OSD is displayed.
> 
> Does putting up the OSD force MythTV to revert to doing the composite
> via software and using Xv for display?  Or can the video and the OSD be
> shipped to the video card using XvMC to be composited and displayed?

I am thinking (Though I have no confirmation on this, just a hunch)
that when the OSD is to be displayed, MythFrontend encodes the OSD's
image into the MPEG stream(s) going to XvMC to be decoded. If this is
the case, then it could be the pauses are the MPEG being decoded,
modified and recompressed on the fly (That or the OSD's image is being
compressed and AND'd into the stream, however it's working)

> Basically I'm wondering if my jumpy playback with OSD CAN be solved in
> XvMC or if I need to buy a faster CPU and use Xv to get smooth playback
> in all cases.

Supposedly, if you want to get faster decoding using Xv, you can use
libMPEG2 (Which is a less CPU-intensive decoder than the default
ffmpeg). However if you are trying to play back HDTV content @ 1080i,
you will still need a fair bit of grunt to decode it.

> Any XvMC developers on this list?  If so, kudos to your XvMC
> improvements.  I've read stories about people's issues with XvMC, but
> I've been using it with a CVS checkout from last week and it's working
> GREAT (except the above).  CPU usage on HD hovers around 45-55%.  Woo hoo!

Yes, XvMC is a great boon. And with the GeForce 6 series' on-GPU
support of MPEG encoding and decoding, support for those processors
would be a great boon also.

Here's hoping these XvMC jitters can be sorted out (And perhaps some
colour added) and them XvMC will be the One True Way(tm)


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