[mythtv-users] Re: Tearing in playback

[Isaac Richards]

On Friday 07 January 2005 07:45 pm, Doug Larrick wrote:
> William Uther wrote:
> > Quick question: how does RTC sync work?
> >
> > RTC stands for Real Time Clock, right?
> > I assume that the frequency has to be higher than the total number of
> > horizontal lines in your X modeline.  If myth then got a known sync
> > signal at any point in the image display it could use that to find the
> > blacking period.  Do you know at what point in the frame the sync signal
> > is sent and how myth gets it?
>
> Actually, the RTC vsync method is not one that synchronizes to the
> vertical retrace... you have to use /dev/nvidia0, OpenGL, or DRI for
> that.  It simply uses the programmable interrupt timer to sleep for an
> accurate delay until it's time to display the next frame.  That said, it
> uses less CPU than "usleep with busy wait," so you are more likely to
> get accurate frame timing.  There's still a possibility of tearing, but
> it will most likely either consistently be OK, or consistently tear (at
> which point you'll probably get fed up and start playback over).

It shouldn't tear if it's using the right Xv port, though, even with RTC or 
busy wait.  Most drivers sync the flip internally to the retrace.

Isaac