fonic/remove-unneeded-languages.sh

## remove-unneeded-languages.sh
#!/usr/bin/env bash

# -------------------------------------------------------------------------
#                                                                         -
#  Remove unneeded language(s) from video file                            -
#                                                                         -
#  Created by Fonic <https://github.com/fonic>                            -
#  Date: 04/14/22 - 11/20/23                                              -
#                                                                         -
#  Posted as answer on StackExchange Unix & Linux:                        -
#  https://unix.stackexchange.com/a/760374/399674                         -
#                                                                         -
#  Published as GIST:                                                     -
#  https://gist.github.com/fonic/51930c3eb5e1ff56b0d9cf204cae1ea9         -
#                                                                         -
#  Based on:                                                              -
#  https://www.reddit.com/r/ffmpeg/comments/r3dccd/how_to_use_ffmpeg_     -
#  to_detect_and_delete_all_non/                                          -
#  https://wiki.sharewiz.net/doku.php?id=ffmpeg:remove_video_audio_       -
#  streams_by_language                                                    -
#                                                                         -
# -------------------------------------------------------------------------

# --------------------------------------
#  Functions                           -
# --------------------------------------

# Print normal/hilite/good/warn/error message [$*: message]
function printn() { echo -e "$*"; }
function printh() { echo -e "\e[1m$*\e[0m"; }
function printg() { echo -e "\e[1;32m$*\e[0m"; }
function printw() { echo -e "\e[1;33m$*\e[0m" >&2; }
function printe() { echo -e "\e[1;31m$*\e[0m" >&2; }

# Print command [$1: command, $2..$n: arguments]
function print_cmd() {
	local output="Command:" arg
	for arg; do
		output+=" "
		if [[ "${arg}" =~ ^(--.+)=(.+)$ ]]; then
			output+="${BASH_REMATCH[1]}="
			arg="${BASH_REMATCH[2]}"
		fi
		if [[ "${arg}" == *[[:space:]]* || "${arg}" == *"$"* || "${arg}" == *";"* || "${arg}" == *"&"* || \
		      "${arg}" == *"\`"*        || "${arg}" == *"~"* || "${arg}" == *"{"* || "${arg}" == *"}"* || \
		      "${arg}" == *"\""*        || "${arg}" == *"#"* || "${arg}" == *"("* || "${arg}" == *")"* || \
		      "${arg}" == *"\\"*        || "${arg}" == *"'"* || "${arg}" == *"<"* || "${arg}" == *">"* || \
		      "${arg}" == *"*"*         || "${arg}" == *"?"* ]]; then
			arg="${arg//\\/\\\\}"; arg="${arg//\$/\\\$}" # [\$"`] need to be escaped as those still
			arg="${arg//\"/\\\"}"; arg="${arg//\`/\\\`}" # have a special meaning even within "..."
			output+="\"${arg}\""
		else
			output+="${arg}"
		fi
	done
	printn "${output}"
}

# --------------------------------------
#  Main                                -
# --------------------------------------

# Set up error handling
set -ue; trap "printe \"Error: an unhandled error occurred on line \${LINENO}, aborting.\"; exit 1" ERR

# Process command line
if (( $# != 3 )); then
	printn "\e[1mUsage:\e[0m   ${0##*/} LANGUAGES INFILE OUTFILE"
	printn "\e[1mExample:\e[0m ${0##*/} \"eng,spa?\" video.mkv video_2.mkv"
	printn "\e[1mExample:\e[0m for file in *.mkv; do ${0##*/} \"eng,spa?\" \"\${file}\" \"out/\${file}\"; done"
	printn "\e[1mNote:\e[0m    LANGUAGES specifies language(s) to KEEP (comma-separated list; add a"
	printn "\e[1m\e[0m         trailing '?' to denote OPTIONAL languages, i.e. no error if missing)"
	exit 2
fi
IFS="," read -a langs -r <<< "$1"
infile="$2"
outfile="$3"

# Sanity checks
[[ -f "${infile}" ]] || { printe "Error: input file '${infile}' does not exist, aborting."; exit 1; }
[[ ! -f "${outfile}" ]] || { printe "Error: output file '${outfile}' already exists, aborting."; exit 1; }
command -v "ffmpeg" >/dev/null || { printe "Error: required command 'ffmpeg' is not available, aborting."; exit 1; }

# Run ffmpeg:
# -i <file>                      specify input file (identified as '0:' in mappings below)
# -map 0:v                       map all video streams from input to output file
# -map 0:m:language:<lang>[?]    map all streams of specified language from input to output file
#                                (option may appear multiple times to specify multiple languages;
#                                trailing '?' means 'optional', i.e. no error if input file does
#                                not contain any tracks for specified language)
# -codec copy                    copy streams as they are without reencoding
# -loglevel warning              output warning and error messages (but no info messages)
printh "Processing file '${infile}'..."
opts=()
opts+=("-i" "${infile}")
opts+=("-map" "0:v")
for lang in "${langs[@]}"; do opts+=("-map" "0:m:language:${lang}"); done
opts+=("-codec" "copy")
opts+=("-loglevel" "warning")
opts+=("${outfile}")
print_cmd "ffmpeg" "${opts[@]}"
ffmpeg "${opts[@]}" || { printe "Error: ffmpeg failed to process file '${infile}'"; exit 1; }
exit 0