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

[Paul Gardiner]

Thomas Hilber wrote:
> 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?

No, I think it just keeps away from both vsyncs, not avoiding
frame dropping completely, but avoiding the repeated dropping.

>> 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.

Yes true.

>> 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.

What about HDMI? Does that count as TV out, or a VGA variant... I
suppose in any case DVI to HDMI can be used in the same way as
VGA to Scart.

Cheers,
	Paul.