[mythtv-users] XvMC unusable with HDTV, Xv won't keep up
joebarnhart at yahoo.com
Fri Oct 8 17:26:22 UTC 2004
I'm caught here. I'm trying to watch HDTV programming
(1080i and 720p sources) and I'm not able to reliably
My system includes a GeForce4 MX card, latest nVidia
6111 drivers, and KnoppMyth on an Athlon 2800. All
drives are DMA, memory is sufficient (1G), etc. I'm
using S/PDIF output for my sound using the alsa
1.0.5rc1 libs. All output is done at 1080i to the VGA
connector, which is hooked to a rear-projection TV
XvMC with 1080i source material:
Playback is fairly smooth, but the system hangs if I
skip forward or backwards. Mythfrontend log shows:
2004-10-08 02:39:55 prebuffer wait timed out..
2004-10-08 02:39:55 waiting for prebuffer...
Over and over. Nothing exits this mode except
Ctl-Alt-Backspace (reboot X server). Video appears to
be down-resolution (maybe 540?) unless I enable "bob"
deinterlace. (Deinterlace should not be needed since
both the output device and input are interlaced.)
Severe artifacts on fine-grained textures when panning
the camera. It appears to be scaled from the
2004-10-08 02:39:06 detectInterlace(Ignore Scan,
Interlaced Scan, 29.97, 1088) - >Interlaced Scan
2004-10-08 02:39:06 Interlaced: Interlaced Scan
video_height: 1088 fps: -1
2004-10-08 02:39:06 Image size. dispxoff 0, dispyoff:
0, dispwoff: 1920, disphoff: 1079
2004-10-08 02:39:06 Image size. imgx 0, imgy: 0, imgw:
1920, imgh: 1080
Xv with 1080i source material:
Playback stutters because the system can't decode the
MPEG fast enough to keep up with the source material.
The deinterlace filter is not needed for high-quality
playback, but the artifacts on fine-grained texture is
XvMC with 720p source material:
The image stutters and jerks back and forth in time
rapidly. CPU utilization is only 5% or so. Sometimes
goes into "slow motion" effect with halting sound.
Xv with 720p source material:
Playback is relatively smooth. Some dropped frames
causing a bit of jerkiness here and there. Strong
aliasing effects with near-horizontal lines exhibiting
severe jaggies. Some sources (e.g. Fox major-league
baseball games) exhibit the same slow-motion effect as
XvMC. I suspect the stream was broadcast as 480p
widescreen (from the moire effects and apparent
resolution), but the mythfrontend saw it as 720p.
I'm very close to a working system, but I can't yet
watch my recorded programs without major troubles.
Some folks in myth-dev had similar problems, but
they've updated their alsa drivers and are all now
happy, leaving me to search again for solutions to my problem.
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