[mythtv-users] Problem recording at 720x576

Bruce Markey bjm at lvcm.com
Wed May 19 20:07:34 EDT 2004

Stephen Longhurst wrote:
> Off the top of my head I can't remember, but I know that everything
> works fine when using 640x480, so I don't think things are inherently
> wrong there.  I get full screen video in myth which I could live with.

You are correct that the number of visible scan lines for PAL is
576. 480 is for NTSC. 480 will work becase it will pick and choose
scan lines. 640x576 or 544x576 may be better choices for you.

> It's just I'm fussy, and I was hoping that 720x576 might sharpen
> things up a bit.

Yes. I'm sure it is a little fussy and fuzzy ;-) but there are a
number of factors involved of which recording resolution is only

Each scan line is an analog signal so it can be sampled at any clocking.
In other words, there is no 'right' horizontal resolution. TV
set are limited in the effective horizontal resolution by the width
of the beam (if there was an infinitely thin, infinitely bright
vertical line on a black background, it would be as bright as the
maximum luma and as wide as the electron beam in motion). The
effective resolution of most good TVs is equivalent to ~500 but may
be much lower for smaller, older or cheaper sets. Also, broadcast
television isn't particularly high (analog) resolution.

Therefore, at some point, higher horizontal resolution won't make
the picture any sharper. Commercial DVRs' highest resolution is
usually 544. Beyond that, the file sizes would be much larger and
more system resources would be used. However, most people couldn't
tell the different between 720, 640 or 544 in a blind taste test.
You may not even be able to distinguish 480.


--  bjm

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