[mythtv-users] XvMC/HDTV/pchdtv observations

Steve Brown sbrown at cortland.com
Sun Nov 30 17:33:05 EST 2003


I'm posting the following comments hoping to discover which of these 
problems others are having and which are of my own making.

DRIVERS/ACCELERATION
Finally got videoout_xvmc and nvidia driver (v1.0.4496) working with my 
GeForce4 MX440. XvMC acceleration seems really essential to decoding 
atsc streams. My 2.8GHz P4 and a debug version of myth isn't up to it. 
With xvmc, I get 60-70% cpu utilization for a 1920x1080i stream. This 
compares to <1% for a 352x480 stream.

The nvidia driver is not quite serially reusable. If you kill 
mythfrontend, rather than normally exiting, the MX440 starts getting 
confused. By about the third time, output hangs and you only get a blue 
screen. An unload/load of the nvidia driver doesn't help, but a reboot 
does. It sure would be nice to be able to force mythfrontend to 
gracefully exit. Currently, hangs are pretty frequent. I don't expect 
nvidia to fix this anytime soon.

The pchdtv bttv kernel driver seems stable, except for an oops if you 
try to rmmod it.

PLAYING RECORDED STREAMS
Some "prebuffering pause" messages along with resulting choppy output. 
Pausing/unpausing doesn't change the behavior.

PLAYING OVER-THE-AIR STREAMS
CHANGING CHANNELS
Makes the prebuffering pause problem much worse. Pause/unpause doesn't help.

I get the assert "last->state & 2" at about xvmcvideo.c:121 if the new 
channel has a different height/width. I tried to update the xvmc stuff 
in libavcodec from the ffmpeg cvs. It didn't make any difference.

Any feedback appreciated,

Steve



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