Currently --script-opt=stats-font_size=n is much bigger than
--osd-font-size=n, which can confuse users, so calculate sizes the same
way.
The \fs value to replicate --osd-font-size is
${osd-font-size} * 288 / 720 with --osd-scale-by-window, and
\fs${osd-font-size} * 288 / ${osd-height}
with --osd-scale-by-window=no. This is because
sub/osd_libass.c:update_playres() sets
track->PlayResY = ass->res_y ? ass->res_y : MP_ASS_FONT_PLAYRESY,
where MP_ASS_FONT_PLAYRESY is 288.
This also works with persistent_overlay=yes.
{\fscx100}{\fscy100} would also replicate --osd-font-size with show-text
and with osd-verlay + --osd-scale-by-window, but not with osd-overlay +
--osd-scale-by-window=no.
The default sizes are multiplied by 720/288 = 2.5 to keep them the same
as before.
