[mythtv-users] XvMC/HDTV/pchdtv observations

[audin at okb-1.org]

On Sun, Nov 30, 2003 at 02:33:05PM -0800, Steve Brown wrote:
> 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.

	I'm just getting into playing with my pcHDTV card.  The card is
currently in a sacrificial PII-300mhz box.  I'm playing the streams on a dual
athlon 2200+ box using netcat and xine.

	The main issue I'm having is that the radeon drivers have buggy Xv
support.  Using Xv for playback results in the right 1/3 of the image showing
the chromakey color (or some other unrelated color...I dunno yet exactly).
Playback using XShm works well, however.

	The other issue is that I want to display the video on my 1024x768 LCD
projector.  So I'm currently planning/hoping to a> fix the radeon Xv support,
b> scale the video to 960x544 centered within the 1024x768 screen (this avoids
aliasing artifacts with scaling to a non-even size).  At the moment one of the
cpus in the box seems to just be able to handle playback with Xshm (a shame
xine isn't well multi-threaded).  The cpu is pretty much pegged, but i haven't
noticed a huge number of dropped frames (mplayer can't keep up, however).

	All of this is on hold until my antenna arrives, however.  The antique
UHF yagi currently duct-taped to my tripod in the living room doesn't quite do
the trick.

	Once playback with xine works well, i hope to set up the pII-300 as a
second backend (the dual athlon has a pvr-250 in it as the primary backend),
but i have to buy more storage for that box first.  I've calculated that the
8gig drive in the PII is enough for about 50 minutes worth of hdtv.  heh.
This also requires convincing mythtv to live with both the pvr-240 and the
pchdtv cards in the same database.

> 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.

	I'm really hoping I can avoid buying an nvidia card.  I'm not
interested in running binary drivers on my dual athlon (it's my
web/mail/file/everything box.  My only other decent machine is my laptop).

	If I really have to (if the radeon driver can't be fixed or the issue
turns out to be a hardware limitation), then I'll probably build a p4-3ghz or
so frontend machine.  I think 3ghz should easily be able to handle playback
without Xv.

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

	I'm pleasantly surprised with the driver.  It works very well.  It
did, however, take me about 2 hours to get it compiled.  The debian patch is
non-functional.  On the other hand it annoys me that one apparently can't
monitor signal strength while grabbing the stream.  I might try to make
grabatsc print signal strength to stderr while it puts the stream to stdout.

-- 
                                            Audin Malmin - audin at okb-1.org

As long as men are free to ask what they must, free to say what they think,
free to think what they will, freedom can never be lost and science can never
regress.			-- J. Robert Oppenheimer