[MPlayer-users] PSNR Question Completed!

[Jan Knutar]

<snip cropped black borders vs no cropped black porders>

> Please can anyone explain why this might be?

You'll get a very high PSNR for the black borders, they are easy to 
encode and affect the average PSNR of the resulting encode.

However, if you would calculate the PSNR of the actual movie without 
the black borders encode, and the PSNR of the movie with black borders 
cropped, you would discover that the PSNR of the actual viewable area 
(the actual movie, without the black borders), whether the black 
borders be encoded or not, would suffer in the non-cropped version, 
because bits are wasted on encoding the black borders. Now... If you 
removed the black borders, the bits used to basically say "Nothing 
here, just black, wow, the source was black, and the encode is totally 
black, what great PSNR!!", you would have more bits for the area that 
acually matters, the movie :)

I explained this poorly, but I hope it provides some insight =/