The --ass-force-style option was only applied when the main libass
library handle was created. Thus any per-file option changes later had
no effect. Do the ass_set_style_overrides() call in per-file
initialization instead so that possible changes will be applied. Also
move the option variable to the option struct.
Current libass will crash (usually) if you set style overrides to a
nonempty value, then an empty one. It'll be easier to trigger this bug
after this commit, but the problem is not on mplayer2 side. The fix is
trivial so hopefully there will be a fixed libass soon.
Turns out it's a bad idea to just always unconditionally use the first
style. Make mplayer2 use and set the style according to the track's
default_style property. Fixes the -ass-styles option broken with
recent libass versions (ticket #40).
