[MEncoder-users] cropdetect cuts off bottom of subtitles

Raphael mencoder at lesshaste.plus.com
Sat Jan 21 15:35:49 CET 2006

RC wrote:
> On Fri, 20 Jan 2006 20:03:20 +0000
> Raphael <mencoder at lesshaste.plus.com> wrote:
>> The part that I chopped out (120 seconds from the beginning) is the
>> same  part as I am testing. So shouldn't cropdetect work on that 120
>> seconds  at least?  
> No.  Any number of things can fool cropdetect.  Logos and all-black
> scense tend to do a good job of that.

That is very odd. I understand that if you cropdetect one part and then 
encode another it can obviously get it wrong. But if you cropdetect the 
same part you are encoding, and the source is a dvd (so no random noise) 
then surely it should just scan from the bottom and top (and left and 
right) until it hits something non-black.  You should then get the 
minimum and maximum in the appropriate directions rounded so that you 
don't chop any of the film out.

>> Also, shouldn't cropdetect round so that you may
>> add a bit of  border rather than risking chopping out important parts
>> of the film?
> No.  Leaving any black border will hurt video compression
> significantly.

Oh well.. More fascinating mencoder oddities to learn about :)


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