#!/bin/bash
trap "rm tmp/* 2> /dev/null; exit" 0 1 2 3 4
mkdir tmp

mkvextract tracks $1 1:tmp/video.h264
mkvextract tracks $1 2:tmp/audio.ac3
ffmpeg -i tmp/video.h264 -i tmp/audio.ac3 -vcodec copy -acodec libfaac -ab 320k -ac 6 -threads 0 -f mp4 $2

rm tmp/* 2> /dev/null
rmdir tmp