[MEncoder-users] cropdetect cuts off bottom of subtitles

Raphael mencoder at lesshaste.plus.com
Sat Jan 21 15:47:08 CET 2006

Raphael wrote:
> 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.

It occurs to me (after talking on IRC) that maybe cropdetect doesn't 
actually store the maximum lit area it ever finds. If this is the case, 
then it is a problem. In my case the subtitles are encoded into the film 
and so you never get the right settings from cropdetect if it 
recalculates per scene without storing the maximum (some subtitles have 
no "p"s and "g"s for example).  Is this what it is doing?


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