[mythtv-users] 720p on CRT/overscan

Alex Halovanic halovanic at gmail.com
Fri Mar 23 02:54:18 UTC 2007

OK, first its worth repeating again, this will never ever work for
Component-Video out (believe me, I've tried, its my current set up).

You have to be running X using a modeline, which I'm not going to get
into the exact details of setting up your X config file, there's more
info here, and a search on the forums will turn up plenty:

Most likely you'll want the ATSC modelines, so lets say you're
succesfully using this 720p one at a resolution of 1280x720 and you
have too much overscan with it:
ModeLine "ATSC-720-60p" 74.25 1280 1320 1376 1650 720 722 728 750

You can see that the numbers 1280 and 720 are in there.  All you have
to do is decrease them to restrict the usable screen size, say to
ModeLine "ATSC-720-60p" 74.25 1144 1320 1376 1650 696 722 728 750

One thing to note, is that any decreases or increases to these numbers
(Except for the 74.25 decimal) must be done in multiples of 8.
Anything less or more than a multiple of 8 will either have no effect,
or start making things look screwy.  You'll probably have to
experiment and restart X a lot unless you're some sort of savant at
estimating pixels.

So while you're screwing around with those numbers, the picture may be
off-center.  The solution to this is here:
The sections on the image being displaced are the ones you want to
try.  The others on narrowing and widening the picture (without
changing the resolution) just plain will never be enough to compensate
for the usual overscan on any set, not within the limited range of
signals they can receive.
The middle two numbers of the horizontal section in my example are
1320 and 1376, the middle two numbers of the vertical section are 722
and 728.  Remember to modify both numbers in the section by the same
multiple of 8.

Keep in mind that you're no longer displaying at the native depth of
the video when using one of these modelines, so there will be a
decrease in video quality, but I don't think a noticeable one.  A
bigger worry might be that if you decrease the number of vertical
lines, Bob deinterlacing may not work as well (if it ever worked).  My
experience has also been that this does not seem to effect XvMC one
way or the other.  I hope this info is helpful to someone.  Let me
know if its unclear.

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