#!/bin/bash

for f in *.mkv
do
    ffmpeg -i "$f" -map 0:s:0 "${f/%mkv/ass}"
    ffmpeg -i "$f" -filter:v subtitles="${f/%mkv/ass}" -c:v libx264 -crf 22 -preset veryfast -c:a copy "${f/%mkv/mp4}"
done

exit 0