[mythtv] Ticket #2903 is necessary to achieve perfect playback with an interleaved display mode.

Thomas Hilber mythtv-dev at toh.cx
Sun Mar 29 14:23:58 UTC 2009

On Sun, Mar 29, 2009 at 03:05:10PM +0100, Paul Gardiner wrote:
> I don't ever notice the dropped frames, but yes they must be there. I'm
> not so sure about the repeated dropped frames. I think MythTv has code
> to keep away from the danger point where the relation is ambiguous.

but how does that work? Does MythTv know something about the field
status of the graphics card?

> I've seen code with comments that said similar, although I didn't
> interpret it in detail. MythTv also can use the video as the timebase,
> adjusting the audio subtly to fit: I think possibly that could avoid
> the frame dropping.

MythTv can adapt replay speed to VGA timing if replaying recordings.
That means stream-recording is synchronized to VGA.

But this approach does not work for live-TV. In that case there is no
other way than to synchronize VGA to stream. The vga-sync-fields patch
synchronizes VGA to stream by introducing variable VGA output frame rates.

> Is vga-sync-fields restricted to VGA, or can it apply equally to
> TV out?

it works only for PAL/RGB compatible modelines on a conventional
Xserver. It does not work for TV out. At least I never tried because
of it's inferior signal quality.


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