[mythtv-users] Assorted Questions about improving MythTV experience

[Bruce Markey]

Robert Schultz wrote:
...
> Thirdly, the 'General Playback' settings.
> I'm watching the recordings and Live TV using yellow composite out to my 
> Sharp 27" televsion.
> If I turn of 'Deinterlace Playback' (since the TV is interlaced) will 
> there be any side effects?
> Does this option affect recording or just playback?

Playback only.

> What about 'Fixed aspect ratio'? Is it wise to turn on, or leave off 
> when I'm using 640x480 (already 4:3) on my TV out?

No effect. In fact, this week it doesn't do anything. For
the 0.9.1 release or earlier, you could switch from full
screen to a windowed picture. The window, by default, would
be shown at the recording resolution which may not be 4:3.
This option is to force the window to be 4:3. With the
recent major improvement of putting everything in one window,
there is no switching between full screen and windowed yet
so this flag doesn't come into play.

> Does anyone have any experience with using 'Jitter Reduction'? Is it 
> helpful or hurtful?

The classic frame timing simply sleeps until it's time to
draw the frame. Since there is a multitask scheduler, it
doesn't actually get the CPU to draw the frame until the
next available time slice. Therefore, each frame is drawn
late to varying degrees, This causes twitches when you watch
a crawler on a news channel for instance.

Jitter reduction tries to be a little smarter by shortening
the sleep so the it gets the CPU early about half the time
then spins a little to make the frame distribution more even.
As the name implies, it isn't perfect but it is smoother at
the expense of spinning about 6% of the time.

> And the 'Experimental A/V Sync'. I've only once so far had to exit Live 
> TV and go back in due to sound and video not matching (which I thought 
> was near impossible with the Pvr250 cards, but I guess not). Just how 
> 'experimental' and dangerous is this option?

No one will be injured, you won't go blind ;-). This uses
a few new trick including checking the video card for where
it is in the refresh cycle. This works particularly well
with nVidia cards and their drivers. This can result in nearly
perfect, jitter free playback. However, there seems to be
problems when software encoding Live TV with the fronted and
backend on the same machine. This is currently being worked on.
The audio and video shouldn't be more than a frame and a half
apart and should normally be within one frame. Either you are
watching very carefully ;-) or something else is going on that
would cause the sync to be noticeably off. Try recording a little
bit of CNN (lips moving and text scrolling) then watch it with
and without Experimental A/V Sync. You need to check both A/V
Sync. and Jitter reduction to run the new code.

--  bjm