[mythtv-users] How I got great quality TV-out on my nVidia MX4000

[Doug Larrick]

John Patrick Poet wrote:
> If someone wanted to buy Doug an Asus Pundit, he *might* be willing to take
> the time to work on improving bobdeint for non nVidia cards, but he is
> unlikely to buy one for himself just for that purpose.

I would not accept any hardware; I barely have time (recently: none at
all) to hack on MythTV for my own purposes.  I certainly would not
accept a low-powered frontend, as all my MythTV-recorded programming is
HDTV.

But really, the hard part of the vsync code is all in the video card
driver.  You card's driver doesn't provide some sort of method of
getting vertical retrace timing?  Complain to the author or
manufacturer, not here.  Or get coding.  Or spend $30 on a new video
card, which is what most of us have decided to do.

If your driver *does* provide a vertical retrace timing method that Myth
doesn't support, it's < 50 lines of code to add a new subclass to
vsync.cpp and plug it in.  This work obviously has to be done by
somebody with the hardware, but there are a half dozen methods there
already, so there's plenty of example code.  And the two methods that
actually sync to hardware are brand-agnostic, one following a Linux
semi-standard (DRM), the other an actual industry standard (SGI OpenGL
vsync).

> Doug would probably be willing to explain how the bobdeint code works, if
> someone without nVidia hardware wanted to work with it.

Bob deint is in two pieces, as I have written in the past:
1. The filter part rearranges the scan lines so that the top field is in
the top half of the video frame, and the bottom field in the second half.
2a. The video output part tells the video output class to display twice
as many frames as usual (e.g. at 50 Hz rather than 25)
2b. ...and arranges to display first the top half (field) then the
bottom half of the frame (or vice versa if the video has these reversed)
at this higher rate.

Note that nothing here has any relation whatsoever to vertical retrace
sync.  That's by design.  Didn't used to be this way, but now it's
fairly clean and modular.

I think much of the reason bob looks *worse* than other deinterlacing
methods for some people is because it's putting twice as much strain on
the video output software and hardware, by displaying at twice the
refresh rate.

Bob deint is designed to output to progressive display devices, such as
HDTVs (or EDTVs) or projectors.  The fact that it sometimes looks better
than non-deinterlaced material on non-progressive displays is an
indication of how *&($#ed up video display in Linux is in general.  I
think if your hardware had a way of getting the vertical retrace, it
would look better w/o a deinterlacer as well.
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