[mythtv-users] Myth scaling/deinterlacing vs Faroudja

Brad Templeton brad+myth at templetons.com
Sun Jun 25 00:58:47 UTC 2006

On Sat, Jun 24, 2006 at 04:37:10PM -0600, John P Poet wrote:
> Sure they are ;-)  The video card has to get the video it sends to the
> TV from somewhere.  In the case of Myth, the video card is being fed
> from data recorded on the hard drive.

Well, sort of.  I don't think of that as a stream since what we really
have is a frame buffer into which video frames are being written like
RAM.   However, it's true it is often done serially.

The card them dumps the frame buffer out as video, either interlaced
or non-interlaced.
> If the video on the hard drive is in an interlaced format, it would be
> nice if it could be "fed" to the video card in that same format, and
> passed onto the TV in that same format.  Unfortunately, I don't
> believe you can "feed" most video cards with interlaced data and have
> it pass it onto the TV.  If I am wrong, then please give me an
> example.

Well, it is tricky.   Some people do it by having a 1920x540 frame buffer
in fake progressive mode at 59.99 fields/second, interlaced, and they
would write in each successive field (2 fields to make a frame.)

But most poeple would have a 1920x1080 frame buffer.  If you output that
in interlaced mode, it will send out one field of even lines, followed
by a 2nd field of the odd lines.     As such, using a basic bob deinterlace
my impression is you would get the same result.  The bob deinterlacer
would place the most recent even frame in the even lines and the most
recent odd frame into the odd lines and it would work as long as you
keep in sync with the frame rate.

All very messy, isn't it?   It's a shame the HD committee didn't sit
down and say, "You know, by the time people can actually afford 1080
line displays, 1080p should not be a problem."   Done at 30fps if that's
what the broadcast channel had bandwith for.

Particularly jarring is that many of the HD things, like movies, are shot
at 24fps, non-interlaced.   I don't know whether the 1080i shows that
are shot on video today are shot at 1080i or some other rate.

Of course the deint in myth isn't too bad but it breaks down on pausing,
audio speed up, ff etc.   I guess with work those motivated could code to
fix that.

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