convert-mp4-to-mkv.sh

#!/bin/bash
#
# convert-mp4-to-mkv.sh
#
# Copyright (c) 2013-2014 Don Melton
#

about() {
    cat <<EOF
$program 1.0 of May 30, 2014
Copyright (c) 2013-2014 Don Melton
EOF
    exit 0
}

usage() {
    cat <<EOF
Convert MP4 video file into Matroska format with single audio track.

Usage: $program [OPTION]... [FILE]

    --help      display this help and exit
    --version   output version information and exit

Requires \`mkvmerge\` executable in \$PATH.
Output is written to current working directory.
EOF
    exit 0
}

syntax_error() {
    echo "$program: $1" >&2
    echo "Try \`$program --help\` for more information." >&2
    exit 1
}

die() {
    echo "$program: $1" >&2
    exit ${2:-1}
}

readonly program="$(basename "$0")"

case $1 in
    --help)
        usage
        ;;
    --version)
        about
        ;;
esac

readonly input="$1"

if [ ! "$input" ]; then
    syntax_error 'too few arguments'
fi

if [ ! -f "$input" ]; then
    die "input file not found: $input"
fi

readonly output="$(basename "$input" | sed 's/\.[^.]*$//').mkv"

if [ -e "$output" ]; then
    die "output file already exists: $output"
fi

if ! $(which mkvmerge >/dev/null); then
    die 'executable not in $PATH: mkvmerge'
fi

readonly identification="$(mkvmerge --identify "$input")"

readonly container="$(echo "$identification" | sed -n 's/^.*container: //p')"

if [ "$container" != 'QuickTime/MP4' ]; then
    die "input file not QuickTime/MP4 format: $input"
fi

readonly track1="$(echo "$identification" | sed -n 's/^Track ID 1: //p')"
readonly track2="$(echo "$identification" | sed -n 's/^Track ID 2: //p')"

if [ "$track1" == 'audio (AAC)' ] && [ "$track2" == 'audio (AC3/EAC3)' ]; then
    audio_tracks='2'
else
    audio_tracks='1'
fi

echo "Converting: $input" >&2

time mkvmerge --output "$output" --audio-tracks $audio_tracks "$input" || exit 1