media-tools/to_opus.sh

#!/bin/bash

# set shopt-options used by this shell-script
# Note, 0 (true) from shopt -q is "false" in a math context.
shopt -q globstar; globstar_set=$?
((globstar_set)) && shopt -s globstar
shopt -q extglob; extglob_set=$?
((extglob_set)) && shopt -s extglob

# return default shopt-options
function finish {
	((globstar_set)) && shopt -u globstar
	((extglob_set)) && shopt -u extglob
}
trap finish EXIT

print_help() {
  printf "Help: not implemented yet"
}

while getopts 'e:' flag; do
	case "${flag}" in
		e) extension+=("$OPTARG");;
		h) print_help
		exit 0;;
		*) exit 1 ;;
	esac
done

# write array into string
extension="${extension[*]}"
# remove leading space
extension="${extension##+([[:space:]])}"
# change separator
extension=${extension// /|}

for file in **/*.@($extension); do

	# array over the number of channels of all streams
	readarray -t channels <<<"$(ffprobe -v error -select_streams a -show_entries stream=channels -of compact=p=0:nk=1 "$file")"
	# array over the bitrates of all streams
	readarray -t bitrates <<<"$(ffprobe -v error -select_streams a -show_entries stream=bit_rate -of compact=p=0:nk=1 "$file")"
	# number of audiostreams
	audiostreams=${#channels[@]}

	# set a channel dependend bitrate for every audio stream
	# https://wiki.xiph.org/Opus_Recommended_Settings
	# to use ffmpegs default just comment out this block
	bitrate_settings=""
	for ((index=0; index<audiostreams;index++)); do
		if [[ ${channels[index]} -eq 1 ]]; then
			if [[ $bitrates == 'N/A' || ${bitrates[index]} -gt 64000 ]]; then bitrate_settings="$bitrate_settings-b:a:$index 64k "; fi
		elif [[ ${channels[index]} -eq 2 ]]; then
			if [[ $bitrates == 'N/A' || ${bitrates[index]} -gt 128000 ]]; then bitrate_settings="$bitrate_settings-b:a:$index 128k "; fi
		elif [[ ${channels[index]} -lt 6 ]]; then
			if [[ $bitrates == 'N/A' || ${bitrates[index]} -gt 256000 ]]; then bitrate_settings="$bitrate_settings-b:a:$index 256k "; fi
		elif [[ $bitrates == 'N/A' || ${bitrates[index]} -gt 450000 ]]; then bitrate_settings="$bitrate_settings-b:a:$index 450k "; fi
	done

	# check if it contains video streams (Thumbnails etc. will be ignored)
	# use mkv for videos and for multiple audio streams
	is_video=$(ffprobe -v error -select_streams V -show_entries stream=codec_type "$file")
	if [[ ${#channels[@]} -gt 1 || -n "$is_video" ]]; then
		command="ffmpeg -i \"$file\" -map 0 -map -0:d -map -0:t -c copy -c:a libopus $bitrate_settings -v info -hide_banner \"${file%.*}.mkv\""
	else
		command="ffmpeg -i \"$file\" $bitrate_settings-v info -hide_banner \"${file%.*}.opus\""
	fi

	eval "$command" #&& rm "$file"
done

exit 0