[MEncoder-users] cropdetect cuts off bottom of subtitles

Raphael mencoder at lesshaste.plus.com
Sat Jan 21 23:55:18 CET 2006

RC wrote:
> On Sat, 21 Jan 2006 14:47:08 +0000
> Raphael <mencoder at lesshaste.plus.com> wrote:
>>> 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.
> Yes, although it might just ignore the subtitles as noise.  Or perhaps
> it's finding the right dimentions, and the rounding is just
> (unfortunately) cutting off (up to) 7 lines off the bottom, which cuts
> off the bottom of your subtitles.
>>> You  should then get the minimum and maximum in the
>>> appropriate directions  rounded so that you don't chop any of the
>>> film out.
> No, it doesn't round the numbers up, always down.  It's that simple.  If
> you don't want it to do that, you can change the default action of
> cropdetect.  See the man page.
> However, if you disable rounding, make sure you use scale to make the
> final dimentions even multiples of 16 before encoding.
>> It occurs to me (after talking on IRC) that maybe cropdetect doesn't 
>> actually store the maximum lit area it ever finds. 
> If you watch the output of cropdetect for a while, you'll see that this
> obviously isn't true.  The dimentions cropdetect outputs NEVER decrease.

Thanks. There appear to be two distinct and contradictory stories on the 
mailing list sadly.  I also noticed that the dimensions never decrease 
which directly contradicts the previous two replies ("The value output 
by cropdetect is the value for the current frame." and "  yes, (I think)
I check only cropdetect on the scene with the most subs. Then I know for 
sure I got all subs and as few as black possible. ")

Also,  what do the "limit" values mean exactly in this part of the man 
page.  What is 24?

 Calculates necessary cropping parameters and prints the  recommended  
 ters to stdout.
               Threshold,  which  can be optionally specified from 
nothing (0)
               to everything (255) (default: 24).


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