With ambient lighting enabled, ASS subtitles anchored to a corner (and PGS
bitmaps) rendered against the whole screen instead of the video: the effect
stretches mpv's frame to the window with video-aspect-override and lets the
shader composite the real picture inside it, and mpv places subtitles against
that stretched frame.
The pinned libmpv now carries --sub-video-rect-aspect (edde746/mpv-build
ec08018), which makes mpv derive its subtitle margins from the picture's real
aspect inside the displayed rect. AmbientLightingService hands it the video
aspect before overriding the frame, so a libmpv without the option refuses
cleanly with the frame untouched, and resets it on disable.
Verified on a Pixel 7 (2400x1080) with a 16:9 file whose OP credits are
\pos-anchored: subtitle extents are pixel-identical with ambient lighting on
and off, and mpv reports OSD borders l=240 r=240 for the overridden frame.
close#2120
edde746
e67bf996c5