Currently this script will convert any audiostream of a .mkv file to EAC3 768k with the same channels (via ffmpeg), then remux these audiostreams to a new .mkv (via mkvmerge)
mkvtoolnix - Matroska tools
ffmpeg - Audio conversion tool
While these apps are available via the default repos on Ubuntu, you can get a newer version of mkvtoolnix via their mkvtoolnix - Repo
Set the following variables inside the script:
# Directory containing the video files
input_dir=“</your/source/folder>“
# Output directory for converted files
output_dir=”</your/target/folder>“
# Temporary directory for AAC audio files
temp_dir=”/tmp/audio_conversion”
# Set new codec
new_codec=“eac3”
# Set new bitrate
new_bitrate=“768k”
If you run the script, it will convert all files inside the “input_dir”, the output file will have all audio streams converted to the set “new_codec” and “new_bitrate” but with the same channels as before. If the original audio stream had 7.1 channels it will be set to 5.1 because ffmpeg EAC3 only supports up to 5.1.
#!/bin/bash # Comment in to see debug messages #set -x # Directory containing the video files input_dir="</your/source/folder>" # Output directory for converted files output_dir="</your/target/folder>" # Temporary directory for EAC3 audio files temp_dir="/tmp/audio_conversion" # Set new codec new_codec="eac3" # Set new bitrate new_bitrate="768k" # Create temporary directory if it doesn't exist mkdir -p "$temp_dir" # Iterate over video files (MKV) in the input directory for file in "$input_dir"/*.mkv; do # Check if the file is a regular file if [ -f "$file" ]; then # Get the base filename filename=$(basename "$file") # Print the current file being processed echo "Processing file: $filename" # Extract audio information using ffprobe audio_info=$(ffprobe -v error -show_entries stream=index,codec_name,channels:stream_tags=language -select_streams a -of csv=p=0 "$file") # Split the audio information into an array of streams IFS=$'\n' read -rd '' -a streams <<< "$audio_info" # Create an array to store the temporary EAC3 audio files temp_files=() # Create an array to store the languages for mkvpropedit languages=() # Iterate over the audio streams for stream in "${streams[@]}"; do IFS=',' read -ra stream_info <<< "$stream" index=${stream_info[0]} codec=${stream_info[1]} channels=${stream_info[2]} language=${stream_info[3]} # Print the current audio stream information echo "Audio Stream $index:" echo "Codec: $codec" echo "Channels: $channels" echo "Bitrate: 768 kbps" echo "Language: $language" # If channels equal 8, change it to 6 (7.1 EAC3 is currently not supported by ffmpeg) if [ "$channels" -eq 8 ]; then channels="6" fi # If language is not set, dont set any metadata, if it is set then set the correct option if [ -z "$language" ]; then lang1="" lang2="" else lang1="-metadata:s:a:0 language=$language" lang2="--edit track:a$index --set language=$language " fi # Create a temporary EAC3 audio file with a fixed bitrate of 768 kbps temp_eac3_file="$temp_dir/${filename%.*}_stream_$index.eac3" ffmpeg -i "$file" -map 0:$index $lang1 -c:a $new_codec -b:a $new_bitrate -ac $channels "$temp_eac3_file" # Construct the temporary EAC3 audio files for mkvmerge temp_files+=("$temp_eac3_file") # Construct the audio stream language for mkvmerge languages+=("$lang2") done # Construct the output filename output_filename="$output_dir/${filename%.*}_converted.${filename##*.}" # Wait for a few seconds before remuxing to ensure the input file is closed sleep 5 # Remux the video and audio streams using mkvmerge mkvmerge -o "$output_filename" -A "$file" "${temp_files[@]}" # Set language metadata for the new audio streams using mkvpropedit mkvpropedit "$output_filename" ${languages[@]} echo "Conversion complete for file: $filename" echo "----------------------------------" # Clean up temporary directory files rm $temp_dir/* fi done # Clean up temporary directory rm -rf "$temp_dir"