nightly-20230218

• merge upstream changes.
• built with ffmpeg 5.1.2, dav1d 1.1.0.

only windows/x64 is supported (ffmpeg fails to build on 32-bit x86).

nightly-20220119

Built with mingw (because vcpkg does not yet support ffmpeg 5.0) and ffmpeg 5.0, so only support VapourSynth (both api3 and api4) and Aegisub.
Apologies to AVS users....

(This build also includes an experimental fix for issue 394.)