[mythtv-users] High-Definition Playback performance data

Paul Leppert phlepper at gmail.com
Tue May 10 14:27:21 UTC 2005


An update based on my latest fiddling and testing:

a) Right drivers for card with your kernel
b) Proper AGP bus speed and AGP interface driver in use
c) Proper user of openGL sync for retrace
d) Proper settings for deinterlace and, if used, xvmc
e) Proper sound settings and handling of 5.1 sound and multiple streams
f) Real time scheduling of playback thread
g) Making sure disk or network speed is adequate
h) Nothing else sucking up CPU on the machine

a) Right drivers for card with your kernel

Check /var/log/<xservername>.0.log.  Excerpt from my
/var/log/Xorg.0.log which shows nVidia driver version 7174:

		(II) LoadModule: "nvidia"
		(II) Loading /usr/X11R6/lib/modules/drivers/nvidia_drv.o
		(II) Module nvidia: vendor="NVIDIA Corporation"
			compiled for 4.0.2, module version = 1.0.7174
			Module class: XFree86 Video Driver

b) Proper AGP bus speed and AGP interface driver in use

	[mythtv at mythtvbe ~]$ cat /proc/driver/nvidia/agp/status
	Status:          Enabled
	Driver:          AGPGART
	AGP Rate:        8x
	Fast Writes:     Disabled
	SBA:             Enabled

c) Proper user of openGL sync for retrace

	Start mythfrontend with the "--verbose playback" option and redirect
	output to a file.  Check for Open GL Sync messages (SGI OpenGL)
	when a recording or live tv is played back.

	mythfrontend.log:
	
		2005-04-25 22:29:36.515 Video timing method: SGI OpenGL

d) Proper settings for deinterlace and, if used, xvmc

	These are set via mythtv in the settings->tv->playback screens
	(deinterlace on the first and xvmc on the fourth or fifth, IIRC).  If
	xvmc is set properly, the OSD will be black and white.  If xvmc
	doesn't show up on the options screen, then it wasn't compiled into
	the program.  If xvmc is used, the "filters" field (which can also be
	used to set deinterlace) isn't used.  My personal opinion is that
	kernel deint appears to give a better picture (in terms of motion
	artifacts) than the others (including BOB).

e) Proper sound settings and handling of 5.1 sound and multiple streams

	I am using ALSA:spdif for sound and I can confirm that it
	works since my DD receiver switches to digital mode.  Not sure what
	exactly to check here, but you can use "aplay -L" to get a listing
	of the ALSA devices set up for your card / .asoundrc file.  Testing
	individual devices can be done with "aplay -D <device> <soundfile>".

f) Real time scheduling of playback thread

	Need to do a couple of things to get this working:
	
	1. chmod u+s mythfrontend
	2. Need to modify /etc/sudoers to add your mythtv user
		(use ALL option and NOPASSWORD; example in sudoers file)
	3. Start mythfrontend with sudo: "sudo mythfrontend &"
	
	At this point the logs should say something like "using realtime priority"

h) Nothing else sucking up CPU on the machine

	Check using "top" and confirm that mythfrontend and X are the top two
	items (X may be lower if XvMC is used).  Remaining items should be
	substantially less (not sure how to define "substantial"...).

Any other suggestions for things to check?
phlepper
-- 
I hear and I forget. I see and I remember. I do and I understand.  --  Confucius


More information about the mythtv-users mailing list