[mythtv-users] Got smooth playback? please post your setup & configuratio

Yeechang Lee ylee at pobox.com
Sun Aug 6 19:04:46 UTC 2006


[James, please don't top post! Edit the text you're responding to!]

James Buckley <xanium4332 at googlemail.com> says:
> [I]t's getting the refresh to be exactly 50Hz which I find the
> hardest.

Here in the US I use a 59.94 modeline. As previously noted, I'm
currently not using Bob, so have thus turned "Enable OpenGL vertical
sync for timing" in mythfrontend off. (Noticeable stuttering
otherwise.)  When I run mythfrontend with -v playback, I see when
playing back a recording from HDNet Movies:

Video timing method: RTC
[...]
'video output' mean '33560.71', std. dv. = '3017.34', fps = '29.98'
 . . . fps = '29.97'
 . . . fps = '29.97'
 . . . fps = '29.98'

Yes, if allowed to settle down for a few moments, the refresh (Or is
"framerate" the proper term?) is rock solid at 29.97 +- 0.01.

When playing back a 720p recording from ABC:

 . . . fps = '59.97'
 . . . fps = '59.97'
 . . . fps = '59.93'
 . . . fps = '59.97'
 . . . fps = '59.96'

Again, excellent refresh-rate performance.

When playing back a movie from the premium-movie channels:

 . . . fps = '23.98'
 . . . fps = '23.98'
 . . . fps = '25.95'
 . . . fps = '26.65'
 . . . fps = '24.17'

*and*, and other points, 

 . . . fps = '29.98'
 . . . fps = '29.98'
 . . . fps = '29.99'

Yes, in many Hollywood movies the framerate/refresh rate (?) jumps
around, seemingly randomly, between 24 and 29.97/30 fps. (I think
there's greater fps variance in the 24fps segments because 3:2
pulldown is more difficult to do right than the simple 1:1 or 1:2
refresh in the other situations.) I saw the same thing a few years
back when transcoding DVDs with mencoder. I'm pretty sure this is the
cause of the still-unresolved
<URL:http://svn.mythtv.org/trac/ticket/1941>.

(Note, also, that for RTC timing to work right, one must first "echo
1024 > /proc/sys/dev/rtc/max-user-freq".)

Now, how does this all play into those of us with LCD monitors, which
of course only do a fixed refresh rate (in my case, 60Hz)? Well, I'm
not sure. I can only theorize that, even if the display shows all
video at 60Hz, getting the refresh rate with the use of a proper
modeline (59.97) and timing method (RTC or OpenGL, depending on
circumstances) is important for smooth playback on the video card's
side.

-- 
Yeechang Lee <ylee at pobox.com> | +1 650 776 7763 | San Francisco CA US


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