[MPlayer-users] Cropping in original-size vs reduced-size

[Nico Sabbi]

Jorge Fábregas wrote:

> Way #1:
> --------------------
> 
> Before encoding:
> mplayer dvd://1 -chapter 4 -vf cropdetect 
> 
> ...to get where to crop exactly
> 
> Actual encoding:
> ... -vf  crop=704:480:8:0,scale=512:384 
> 
> Way #2:
> ------------------
> 
> Before encoding:
> mplayer dvd://1 -chapter 4  -vf scale=512:384,cropdetect
> 
> ...Notice here that in order to get the proper crop values I'm actually 
> dowscaling first..thus I'll get the values for the downsized image.
> 
> Actual encoding:
> ... -vf  scale=512:384,crop=496:384:8:0
> 
> 
> Could you guys please tell me which on is the best one? In Way#1 I'm scaling 
> to 4:3 the ACTUAL content.  In Way #2 I'm scaling the WHOLE frame.  Obviously 
> these are 2 different things. Ok, for the regular eye, there won't be much 
> difference but I think Way#2 is the way to go.  In Way#2 even though I end up 
> with 496x384 (which isn't 4:3) the thing is that this frame was cropped from 
> a 4:3 one (which already considered square pixels).
> 

cropping weighs next to nothing on the cpu, thus performance will not 
be sensibly better with method #2; on the other side the contrast 
between black bands and actual video leads to an inefficient 
utilization of the bitrate at disposal of the encode, so #1 is 
preferrable.
As I wrote in my previous mail in both cases you will distort your 
encode if you don't use scale=x':-10


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