FFmpeg Batch calc

set bitaudio=90
set timesecond=35
set /a bitvideo = 32768 / %timesecond% - %bitaudio%
set filepath=
set metadata=
set outputname=
set ss=
set t=
set size=
set an=

ffmpeg -y %ss% -i "%filepath%" %t% -c:v libvpx -b:v %bitvideo%k %size% -c:a libvorbis -b:a %bitaudio%k %an% -pass 1 -metadata title="%metadata%" -f webm NUL
ffmpeg -y %ss% -i "%filepath%" %t% -c:v libvpx -b:v %bitvideo%k %size% -c:a libvorbis -b:a %bitaudio%k %an% -pass 2 -metadata title="%metadata%" "%outputname%.webm"