aspect: add --video-recenter

This ignores --video-align-{x,y} when the video is smaller than the window in the respective direction. After zooming in, panning and zooming out, this is useful to recenter the video in the window. Unlike doing this by observing osd-dimensions in a script, this is done before rerendering, so you don't see the image being rendered uncentered for an instant after zooming out, before being rerendered centered. Also update --video-align docs while at it. This doesn't work well with --video-pan-{x,y} because you can move the output rectangle far away from the image, and when zooming out pan is abruptly reset to the center. It doesn't feel like natural like zooming out after changing --video-align-{x,y}. So this commit doesn't set pan to 0. Also this leaves a way to move scaled images within the window even with --video-recenter.

GCGuido Cella committed 1 year ago