Cory Papenfuss wrote:
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)
Well, I was kinda hoping the mythtv frontend by itself would read the
contents of /usr/lib/mythtv/filters/* by itself,
(I guess that's the java-damage I talked about). After finding
"bobdeint" inside libmythtv-0.18.1.so I understand
there's no easy way out.
The filters seem simple enough, but I've yet to understand why bobdeint
(which i'm using as a template)
works at twice the framerate while the other filters do not.
I'd appreciate any help I can get. I'm working on the source dist, not
SVN, but I'll be looking to get my filter
added to it if I get it working.
--
bjornko
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