[mythtv] MPEG2 IDCT acceleration

Brad Corrion bcorrion at web-co.com
Tue Apr 20 11:59:31 EDT 2004


I gave the patches a run last night and am impressed.  I'm now using XvMC
100% thanks to the patches.  My system is a 2.6 Ghz HT P4, w/ GF 440 MX. 
I almost bailed on them, but then I turned off b-frame skipping, and all
is well.  I played with the sliders and couldn't find a setting that
eliminated stuttering on my CBS and PBS stations.  When I turned b-frame
skipping off, I only have stuttering at the beginning of recordings, when
the OSD is fading, and after a pause.  Once the system levels out, the
playback is nice.


> I've made a regular patch of the playback stuff, with idct acceleration.
> It's at    http://www.mrl.nyu.edu/~danielk/mythtv/
> It works with all my videos, but they don't fully exploit MPEG2. I've
> streamlined the xvmc packet parsing again so there is less redundancy
> and it's also more readable. It's also using less if's which is
> especially important for today's speculative execution processors. If
> you optimize for the CMOV instruction (686+) a lot of the jumps just go
> away. I can now almost play 1040i streams without B-Frame skipping with
> a FX5200 card. (Every few minutes there is a hickup.)
> -- Daniel
> On Fri, 16 Apr 2004, Daniel Thor Kristjansson wrote:
> ]
> ]I've put a new patch at
> ]  http://www.mrl.nyu.edu/~danielk/mythtv/playback.patch.bz2
> ]  plus this file to place in libs/libmythtv
> ]  http://www.mrl.nyu.edu/~danielk/mythtv/XvMCSurfaceTypes.h
> ]
> ]It's incompatible with my other patches at the moment, but will patch
> ]CVS cleanly. This playback patch will use the idct acceleration
> ]available on newer video cards if it is available. This reduces the
> ]amount of data that needs to be sent through the AGP bus for I-Frames
> ]and reduces the amount of math the CPU has to perform.
> ]
> ]I can now watch 720p channels with OSD and no frame skipping.
> ]
> ]-- Daniel
> ]
> ]On Wed, 14 Apr 2004, John Patrick Poet wrote:
> ]
> ]]
> ]]On Wed, 14 Apr 2004, Daniel Thor Kristjansson wrote:
> ]]
> ]]>
> ]]> I've updated my patches so the work against the latest CVS.
> ]]>
> ]]> No real change in functionality, except the hdtv-playback patch now
> lets
> ]]> you disable frame skipping, or tune it to work with your system. The
> ]]> signal check threshold can also be set by the user, but the ui for it
> is
> ]]> in the playback patch for now.
> ]]
> ]]Hey Daniel,
> ]]
> ]]I noticed that the frontend spits out message along the lines of "frame
> skip
> ]]ratio", or some such.  I assumed that this message was part of your
> code,
> ]]and indicated a need to skip frames to "keep up".
> ]]
> ]]However, I also see these message from mythcommflag.  Why would the
> ]]commercial skipping detector need to skip frames to "keep up"?
> ]]
> ]]I use your patches, but do not currently have XvMC enabled.  Even with
> your
> ]]patches, enabling XvMC causes my output to studder more than with out
> it.
> ]]Do I not have something configured right?
> ]]
> ]]Thanks for all the work you have put into this.
> ]]
> ]]John
> ]]
> ]
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