[FFmpeg-user] How to brighten part of a dark video?

[Gilles]

On Fri, 18 Sep 2015 14:25:27 +0200, Moritz Barsnick <barsnick at gmx.net>
wrote:
>Small hint: You probably want the same x, y coordinates for the overlay
>as you used for the crop, so as to place the corrected part at exactly
>the same place. ;-)

Indeed, thanks for point it out.

Out of curiosity, is it possible to soften the edges of the cropped
part so it's a bit less obvious?

Currently, it has hard edges, so that part stands out.