A script to concatenate media files with matching codecs.

concatenate-videos.sh

#!/bin/bash
set -euo pipefail

# A script to concatenate media files with matching codecs.
# Copyright (C) 2021  Clay Freeman
# 
# This program is free software; you can redistribute it and/or
# modify it under the terms of the GNU General Public License
# as published by the Free Software Foundation; either version 2
# of the License, or (at your option) any later version.
# 
# This program is distributed in the hope that it will be useful,
# but WITHOUT ANY WARRANTY; without even the implied warranty of
# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
# GNU General Public License for more details.
#
# The license for this software can be found at the link below:
# https://www.gnu.org/licenses/old-licenses/gpl-2.0.en.html

# Create a temporary file to hold the list of inputs.
FILE_LIST="$(mktemp)"

# Define a function used to clean up the temporary file list.
function clean_up() {
  rm -f "$FILE_LIST"
}

# Define a function used to print a help message.
function print_help() {
  if [ -n "${1-}" ]
  then
    echo "ERROR: $1" 1>&2
    echo 1>&2
  fi

  echo "Usage: $0 output input [...]" 1>&2
  exit 1
}

# Set up trap functions to capture certain events.
trap clean_up EXIT
trap print_help ERR

# Extract the name of the output file from the first argument.
OUTPUT_FILE="${1-}"

# Ensure that an output file was supplied.
if [ -z "$OUTPUT_FILE" ]
then
  print_help "An output file is required."
else
  shift
fi

# Build the input file list from all remaining arguments.
for file in "$@"
do
  # Only add this file to the input list if it actually exists.
  if [[ -f "$file" ]]
  then
    HAS_INPUT=1
    printf 'file %q\n' "$(realpath "$file")"
  fi
done > "$FILE_LIST"

# Ensure that there is at least one input file.
if [ -z "${HAS_INPUT-}" ]
then
  print_help "At least one input file is required."
fi

# Log the job description to the error output stream.
cat <<EOF 1>&2
Output: "$OUTPUT_FILE"

Inputs
======
$(cat "$FILE_LIST")

EOF

# Concatenate the input files into a single file by copying.
ffmpeg -f concat -safe 0 -i "$FILE_LIST" -c copy "$OUTPUT_FILE"