more later
here is the code I used

@Echo off
SETLOCAL
for %%f in (*.mkv) do (
ffmpeg -y -i "%%~f" -map 0:s:0 subtitles.ass
ffmpeg -y -i "%%~f" -vf subtitles="subtitles.ass" -map 0:0 -map 0:1 -c:v:0 libvpx-vp9 -crf 32 -b:v 0 -c:a:0 libopus -cpu-used:v 0 -deadline best -tile-columns 4 -frame-parallel 1 -threads 8 -metadata:s:v:0 title="%%~nf" -metadata title="%%~nf" -pix_fmt yuv420p -pass:v 1 -f webm NUL
ffmpeg -y -i "%%~f" -vf subtitles="subtitles.ass" -map 0:0 -map 0:1 -c:v:0 libvpx-vp9 -crf 32 -b:v 0 -c:a:0 libopus -cpu-used:v 0 -deadline best -tile-columns 4 -frame-parallel 1 -threads 8 -metadata:s:v:0 title="%%~nf" -metadata title="%%~nf" -pix_fmt yuv420p -pass:v 2 "%%~nf [ENG-SUB_2pass499_yuv420p].webm"
)
PopD
shutdown.exe /h
Pause

the "shutdown.exe /h" part puts the windows machine in hibernate mode when it's done encoding so the computer does not waste power doing nothing when it's on