By default, libass scales subtitle with video size.
When --sub-scale-with-window is enabled, mpv attempts to undo this scale
and use window size instead. However, the current bahavior is incorrect
when use_margins is enabled, because in this case libass uses the size
of video as if it's "fit" to the window, instead of the displayed size.
As a result, subtitle scale is broken when video-zoom is used in this case:
when zooming out video, the subtitle is scaled up.
Fix this by using the correct factor when use_margins is enabled.
nanahi
42e9f302df