Daniel Kristjansson wrote:
I'm not sure if a Sempron 64 1600+ can
do software decoding of HDTV. If it can, you should use that.
The Sempron 64 2600+ (1600 mhz) pushed to 2000 mhz still doesn't have
enough horse power to to software decoding HD. The processor is only
running about 30% while using XvMC and playing HD in 18.1. I also
compiled the Debian source packages with athlon-xp and mmx options.
It took me a good three weeks to the HD-3000 card to work properly. I kept
getting the "A/V diverged by 4.28889 frames, extending frame to keep audio in
sync" errors whenever I had the sound enabled on MythTV. Disable the sound and
720p and 1080i would play flawlessly. Enabled sound, and the dropping frames
would occur again.
I think the A/V diverged code is somewhat broken,
but that just amplifies the nVidia XvMC problem.
I wonder why when I disabled the sound in MythTV HD played perfectly
using XvMC. That was very strange.
Nothing worked, until I changed the DVB recording buffer options. MythTV
defaults with 8192 for "Per PID driver buffer size" and "Packet buffer". I
changed this to 16464 and HDVD played flawlessly (well, as good as XvMC and OSD
can play nice together). So the problem doesn't appear to be sound related,
just how much buffer was available to fit the signal.
Hmm, interesting. I might just up the buffer by default...
Under 18.1, and increasing the buffers, HD does play perfectly even with
the bob deinterlace running. The only issue appears when OSD and XvMC
is used, and that causes a few dropped frames and stuttering while the
OSD is on the screen. Actually, I think I remember reading that it was
the fading out of the OSD that was messing up XvMC.
Does SVN no longer use the buffer settings?
It should still respect those settings.
Then I wonder if something else that has been changed. Because 18.1
plays great (after increasing the buffers) except for the OSD flutter.
But the new SVN has the same problems that 18.1 did when I had the
default settings on the buffers.
Sure. The XvMC code used to cause machines to lock up and require a
hard-reboot back in the 0.16 days, in 0.17 and 0.18 we added some
X11 locking, preventing the Linux kernel lockups. We also reserved
two surfaces for blending the OSD to the display frame, preventing
the mythfrontend itself from locking up. This made XvMC safe to use,
but also made it impractical to use it for HDTV, at least with the
nVidia drivers/hardware. It works fine for HDTV on HDTV capable
VIA XvMC hardware;
I think I remember reading that the VIA XvMC is limited to something
like 1024x768 resolution and it doesn't do native HD resolutions.
but there you have 16 XvMC surfaces, rather than
the 8 that nVidia gives you. If you think about it, after allocating
one frame for display, two for blending, one for the last I/P frame,
one for the next I/P frame, and one for the currently filling B frame,
then you only have 2 frames left for buffering. You need really fast
graphics hardware and a really fast main processor to make that work
at 1920x1080... It is cheaper to buy a less fast main processor
(2.8Ghz P4) and use software MPEG2 decoding, plus you get higher
quality results.
Well, the results are that the Sempron 64, even running at 1600 mhz,
with the nVidia FX5200 card can handle MPEG2 decoding without a problem
using XvMC. Xine and XvMC work fine. 18.1 works fine except for the
OSD flutter. Can I provide you with any frontend logs that would better
show what is going on?
Someone had promised to implement a chromakey based XvMC OSD, which
would free up the crucial blending surfaces and make HDTV viable with
the limited nVidia drivers/hardware, but he didn't deliver. Anyway,
implementing chromakey OSD is now on my MythTV TODO list for after
the next MythTV release. Chromakey OSD wouldn't look as nice, it
would in fact look like the mplayer OSD, but it would free up 2 XvMC
surfaces. So you have a buffer of 4 frames rather than 2. My tests
showed this is sufficient for non-sports programming @ 1920x1080
to work well on a P4 @ 1.8 Ghz.
I read that someone was working on the chromakey XvMC OSD. I was
looking forward to that. Bummer it didn't get completed in time.
Currently with 18.1, I can watch 1920x1080i and 720p programming (sports
and non-sports) and not drop a single frame (minus the OSD problem). I
have the front end logging all the time so I can watch what is going on.
Still, it's strange that if I turned off the sound, MythTV would play HD
fine but after I turned sound back on, diverged frames.
I think if we can possibly isolate the changes in the DVB code between
18.1 and the current SVN, it will gives us some insight into what is
occuring and make HD work for XvMC in the current SVN. Though the
differences might be so vast it might be a huge deal.
Chris
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