ffmpeg-mkv-to-mp4

#!/bin/bash

set -euo pipefail

run() {
    echo >&2 "+ $*"
    "$@"
}

if [ $# -lt 1 ] || [ $# -gt 2 ]; then
    cat >&2 <<EOM
usage: $(basename "$0") INPUT.mkv [OUTPUT.mp4]

Losslessly repackage .mkv container video files to .mp4 container, which makes
native playback possible on Android.

Under the hood, this will keep the video codec as-is (expected to be H264),
and keep the audio codec as-is (expected to be AAC).
EOM
    exit 1
fi

input="$1"

if [ $# -ge 2 ]; then
    output="$2"
else
    output="$(dirname "$input")/${input%.???}.mp4"
fi

run ffmpeg -i "$input" -c:v copy -c:a copy "$output"

echo "Successfully wrote $output"