[mythtv] Filter interface change proposal, working on patch.

[Jim Paris]

> I'm planning to port and/or write some good deinterlace and detelecine
> filters for use in recording.  Good handling of interlaced video requires
> chroma data for each line, so I'm working on adding the following:

Wow.  I was just looking into the possiblity of adding better
deinterlacing.  Nice coincidence.

> A new function would be added in filters.c, filters_setup(int &width, int
> &height, int &inpixelformat, int &outpixelformat, VideoFilter **filters,
> int numberfilters), and would be used by filter clients to set up the
> entire filter chain.  Width and height would be modified by filters which
> change the frame size.  With this interface, overscan could be handled
> entirely by a filter.

You're also going to want to be able to change the framerate (for
deinterlace and detelecine).  I'm not sure how that would work in
terms of the video buffers, since you could be returning more or less
data than you're given.

This has less to do with the filters and more with their integration
in Myth, but another point is that some filters may be too slow to run
in realtime.  It would be nice if there was a way to, say, specify
that we should use deinterlacer "linearblend" while playing an
interlaced video but use "deinterlacesmooth" while transcoding it.
(see http://home.bip.net/gunnart/video/, 
     http://home.bip.net/gunnart/video/AVSPorts/SmoothDeinterlacer)

-jim