Find all MKV files below a source directory and create a 2s long snippet of each found file below a target directory while preserving the directory structure.

shortenmkv.sh

#!/bin/bash
set -e
set -u

# Cannot use /bin/sh due to process substitution in run().

VERSION="20170711"

FIND=/usr/bin/find
MKDIR=/bin/mkdir
SORT=/usr/bin/sort
PWD=/bin/pwd
FILE=/usr/bin/file

# Install through homebrew with
# brew install ffmpeg --HEAD --without-libvo-aacenc --without-qtkit
FFMPEG=/usr/local/bin/ffmpeg
FFMPEG_LOGGING_ARGS=( "-loglevel" "warning" )
#FFMPEG_LOGGING_ARGS=( "-loglevel" "info" )
FFMPEG_BASE_ARGS=( "-hide_banner" )

# ######### TODO these values are not really user configurable right now #####
ABS_CURRENT_DIR=$("${PWD}")
# ############################################################################

# No user configurable options below this line.
# --------------------------------------------------------------------------------
function usage()
{
	printf %s '
Version:
'"${VERSION}"'

Usage:
'"${PROGRAM}"' [-v] [-j] [-x] srcdir targetdir

-v increases the verbosity level. A higher level means more output to stdout.
   Level 0: Warnings and errors only.
   Level 1: Processed files.
   Level 2: Executed commands.

-j writes a job summary to stdout and exits.

srcdir is the directory with the MKV files.

targetdir is the directory where the shortened MKV files are created.

Always use double quotes around names with spaces, or things won'"'"'t work.
'
}

# ----------------------------------------------------------------------------
function log()
{
	local message="$1"
	local verbosityLevel=$2

	if (( VERBOSITY >= verbosityLevel )); then
		echo "${message}"
	fi
}

# --------------------------------------------------------------------------------
function logRun()
{
	local commands=("$@")

	# Read the last element (i.e. the verbosity level)
	local verbosityLevel="${commands[$(( ${#commands[@]} - 1 ))]}"

	# Remove last element (the verbosity level) from the commands array.
	unset commands[$(( ${#commands[@]} - 1 ))]

	if (( VERBOSITY >= verbosityLevel )); then
		(set -x; "${commands[@]}")
	else
		"${commands[@]}"
	fi
}

# --------------------------------------------------------------------------------
function shortenMkv()
{
	local absSrcFile="$1"
	local absTargetFile="$2"

	local ffmpegInputArgs=( "-i" "${absSrcFile}" )
	# Encode 2s only.
	local ffmpegTestArgs=( "-ss" "00:00:00" "-t" "2" )
	local ffmpegAudioArgs=( "-flags" "+global_header" "-map" "0:a" "-map" "-0:s" "-map" "0:v" "-map_metadata" "0" "-c:a" "copy" "-c:v" "copy")

	local ffmpegAllArgs=(
			"${FFMPEG_LOGGING_ARGS[@]}"
			"${FFMPEG_BASE_ARGS[@]}"
			"${ffmpegTestArgs[@]}")

	ffmpegAllArgs+=(
			"${ffmpegInputArgs[@]}"
			"${ffmpegAudioArgs[@]}"
			"${absTargetFile}")

	log "-----------------------------------------------------------------------" 2
	log "Shortening '${absSrcFile}'..." 1
	logRun "${FFMPEG}" "${ffmpegAllArgs[@]}" 3
	log "Done." 3
}

# ----------------------------------------------------------------------------
function showJobSummary()
{
	local absSrcRootDir="$1"
	local absTargetRootDir="$2"

	local params=(
			"${absSrcRootDir}"
			"${absTargetRootDir}")

	printf "
-----------------------------------------------------------------------
I would shorten all *.mkv files in source directory to target directory.

Source directory : '%s'
Target directory : '%s'
-----------------------------------------------------------------------
" "${params[@]}"
}

# --------------------------------------------------------------------------------
function run()
{
	local absSrcRootDir="$1"
	local absTargetRootDir="$2"

	if (( JOB_SUMMARY )); then
		showJobSummary "${absSrcRootDir}" "${absTargetRootDir}"
		exit
	fi

	while read -d '' -r -u3 absSrcFile; do
		local absTargetFile="${absSrcFile/${absSrcRootDir}/${absTargetRootDir}}"

		if [ ! -d "${absTargetFile%/*}" ]; then
			log "-----------------------------------------------------------------------" 2
			log "Creating directory..." 2
			logRun "${MKDIR}" -p "${absTargetFile%/*}" 3
			log "Done." 3
		fi

		shortenMkv "${absSrcFile}" "${absTargetFile}"
	done 3< <("${FIND}" "${absSrcRootDir}" -type f -name \*.mkv -print0 | "${SORT}" -z)
}

# ----------------------------------------------------------------------------
# ----------------------------------------------------------------------------
# ----------------------------------------------------------------------------
PROGRAM="${0##*/}"
VERBOSITY=0
JOB_SUMMARY=0

while getopts ":vj" optname; do
	case "$optname" in
	"v")
		(( VERBOSITY++ ))
		;;
	"j")
		JOB_SUMMARY=1
		;;
	"?")
		log "Invalid option: -$OPTARG" 0 >&2
		exit 1
		;;
	":")
		log "Option -$OPTARG requires an argument." 0 >&2
		exit 1
		;;
	esac
done

shift $(( OPTIND - 1 ))

if [ $# -ne 2 ]; then
	usage
	exit 1
fi

# http://www.network-theory.co.uk/docs/bashref/ShellParameterExpansion.html
if [ -d "${ABS_CURRENT_DIR}/${1}" ]; then
	absSrcRootDir="${ABS_CURRENT_DIR}/${1%/}"
elif [ -d "${1}" ]; then
	absSrcRootDir="${1%/}"
else
	log "Invalid srcdir: '${1}'" 0 >&2
	exit 1
fi

if [ -d "${ABS_CURRENT_DIR}/${2}" ]; then
	absTargetRootDir="${ABS_CURRENT_DIR}/${2%/}"
elif [ -d "${2}" ]; then
	absTargetRootDir="${2%/}"
else
	log "Invalid targetdir: '${2}'" 0 >&2
	exit 1
fi

run "${absSrcRootDir}" "${absTargetRootDir}"

log "-----------------------------------------------------------------------" 2
log "All done." 1