mkv2m4v.sh

#!/bin/bash
#
# mkv2m4v inputfile.mkv
#
# Given an MKV container with H.264 video and AC3 audio, converts
# quickly to an iPad-compatible MP4 container without re-encoding the
# video (so it must already be in an iPad-compatible resolution); the
# audio is downmixed to stereo with Dynamic Range Compression.
#
ME=$(basename $0)
 
usage() {
    echo "usage: ${ME} inputfile.mkv" 1>&2
    exit 1
}
 
message() {
    echo ${ME}: "$@"
}
 
error() {
    message "$@" 1>&2
    exit 1
}
 
checkdep() {
    [ ! -z $(which "$@") ] || error "Can't find dependency:" "$@"
}
 
checkdep mkvmerge
checkdep mkvextract
checkdep a52dec
checkdep faac
checkdep MP4Box
 
INFILE="$1"
shift
 
if [ "${INFILE}" == "" ]; then
    usage
fi
 
if [ ! -r "$INFILE" ]; then
    error "Can't read $INFILE"
fi
 
DESTDIR=$(dirname "$INFILE")
 
INFILE_BASE=$(basename "$INFILE")
BASE=$DESTDIR/${INFILE_BASE%.*}
 
message "Analyzing Matroska ..."
mkvmerge -i "${INFILE}" > "${BASE}".tid
 
AC3TID=$(grep A_AC3 "${BASE}".tid | perl -ne '/(\d+)/ and print $1')
AVCTID=$(grep AVC "${BASE}".tid | perl -ne '/(\d+)/ and print $1')
 
if [ "${AC3TID}" == "" ]; then
    error "Couldn't find AC3 stream"
fi
 
if [ "${AVCTID}" == "" ]; then
    error "Couldn't find AVC stream"
fi
 
message "Demultiplexing Matroska ..."
mkvextract tracks "${INFILE}" ${AC3TID}:"${BASE}".ac3 ${AVCTID}:"${BASE}".264
 
message "Downmixing AC3 ..."
a52dec -o wav "${BASE}".ac3 > "${BASE}".wav
 
message "Encoding audio for MP4 ..."
faac -b 96 --mpeg-vers 4 -o "${BASE}".aac "${BASE}".wav
 
message "Creating MP4 container ..."
MP4Box -add "${BASE}".264:fps=23.976 -add "${BASE}".aac "${BASE}".m4v
 
message "Cleaning up ..."
rm "${BASE}".{tid,264,ac3,wav,aac}