[mythtv] Idea for interlaced playback.
Cory Papenfuss
papenfuss at juneau.me.vt.edu
Thu Nov 10 16:16:48 EST 2005
> Three things are needed for proper interlaced playback:
> 1) You need perfect line matching between the video framebuffer and
> the tv-raster-lines. This can (at least on my nvidia card) be solved
> with a proper modeline and overscan-settings. No form of rescaling must
> be allowed as this will blend the fields together.
>
> 2) You need to synch at the field frequency.
> With xv or the OpenGL synch function, this is no problem.
> I'm not sure if OpenGL or XV will blur odd/even lines together. This
> might be a problem.
>
> 3) You need to update half the lines (one field) at one refresh, and the
> other half at the next (but not removing the previous field)
> rinse, repeat.
>
> Some people seem to think you need to know when the TV-out is doing a
> odd-line or even-line refresh, which is not easy at all. But this is
> incorrect, all you need to do is make sure odd-field lines are only in odd
> lines in the framebuffer and the same for the even fields and update the
> fields in order. (This is known as "bob and weave")
>
I'm quite interested in this, because I use homebuilt hardware to
directly connect VGA to s-vid on my TV. I drive the VGA at NTSC
frequencies directly and have always had great quality. Trouble is that
the VSYNC seems to be ignored (as you say). The result is a tearing that
can only be band-aided by enabling something like kerneldeint.
I was unaware that plain ol' XV had the ability to sync, but now I
see (with xvinfo on my main machine, not my mythtv machine):
"XV_SYNC_TO_VBLANK" (range 0 to 1)
client settable attribute
client gettable attribute (current value is 1)
Interesting...
-Cory
--
*************************************************************************
* Cory Papenfuss *
* Electrical Engineering candidate Ph.D. graduate student *
* Virginia Polytechnic Institute and State University *
*************************************************************************
More information about the mythtv-dev
mailing list