re-encode videos to H.265, specifying source and target container format (fish shell)

tox265.fish

set FROM_EXT mp4
set TO_EXT mkv
set ABR 128k
set CRF 22
for i in *.$FROM_EXT 
  set BASENAME (basename $i .$FROM_EXT)
  set DIRNAME (dirname $i)
  nice -n 19 time ffmpeg -i "$DIRNAME/$BASENAME.$FROM_EXT" -vcodec libx265 -crf $CRF -ac 2 -c:a libmp3lame -b:a $ABR output.$TO_EXT; and \
    mv output.$TO_EXT "$DIRNAME/$BASENAME.$TO_EXT"; and \
    rm "$i"
end

Audio is recoded too - target audio is hardcoded to mp3 stereo here (-ac 2: 2 channels, -c:a libmp3lame: use mp3lame encoder for audio).