[MPlayer-users] cropdetect doubt

Corey Hickey bugfood-ml at fatooh.org
Sun Jan 18 22:32:51 CET 2004

pablo.morales at abitab.com.uy wrote:
> Great, now, which values should I pass to the crop parameter, the ones that are 
> constant to the rest of the movie?

The way cropdetect works is to find values based on the current frame,
but not to exceed the cropping it has decided for previous frames. You
might notice that at the beginning, when the whole picture is black,
cropdetect would crop out the entire frame. :) The easiest way to use
cropdetect quickly is to seek a few times into the middle of the movie,
and make sure that cropdetect sees a scene that fills the entire frame.
Once that happens, the printed values will stabilize, and that's what
you should use.

After that, pass the cropdetect values to -vf crop or -vf rectangle, and
adjust them as necessary to get rid of any fuzzy edges. Dominik
mentioned multiples of four for the cropping values, but as far as I
know it is only helpful to keep the values even numbers (both the crop
dimensions and the offsets should be even; there should be no odd
numbers in your crop= parameters). The exception to this is when you are
cropping interlaced/telecined video, in which case the vertical offsets
and dimensions _do_ need to be multiples of four.

> I'm using -scale 640:480, for a movie of an 1 hour an half and a bitrate of 
> 1900, and the vcodec:mpg4 vhq vqlim, vlelim, dark_mask and lumi_mask parameters 
> that appear in the encoding-tips.txt that comes with the documentation.

encoding-tips.txt is somewhat outdated...

You may want to rethink using the *elim and *_mask parameters. Rich
originally suggested them, but last I've heard he thinks they may not be
such a good idea; I've said this a couple times, and he hasn't corrected
me :). They degrade the picture quality somewhat, and I think they
aren't really worth it.

vhq has been superceded by mbd=2. Use that instead.

You should also use trell. trell and mbd=2 are probably the two best
quality-increasing options you can use (for a given bitrate, of course).


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