Converting FLAC to OPUS

I am currently rebuilding my music library from scratch so that I can effectively archive all the music I own in the FLAC file format, a lossless audio codec.

However, streaming FLAC files outside the home can be difficult due to the size of the files, especially if you're using a weak connection.

So, in order to archive the music in a lossless format and still be able to stream it easily, I opted to create a copy of my FLAC files in the Opus audio codec. This allows me to archive a quality, lossless version of the music and then point my streaming service to the smaller, stream-ready version.

Dependencies

The process I follow utilizes the opus-tools package in Ubuntu. Before proceeding, install the package:

sudo apt install opus-tools

If you want to use a different conversion method, such as ffmpeg or avconv, simply install that package instead.

Conversion Process

The script I'm using is stored in my home directory, but feel free to create it wherever you want. It does not need to be in the same directory as your music files.

cd ~ && nano transform.sh

Once you have your new bash script opened in an editor, go ahead and paste the following logic into the script.

You MUST edit the following variables in order for it to work:

• source: The source directory where your FLAC files are stored.
• dest: The destination directory where you want the resulting Opus files to be stored.

You MAY want to edit the following variables to suit your needs:

• filename: If you are converting to a file format other than Opus, you'll need to edit this so that your resulting files have the correct filename extension.
• reldir: This variable can be edited to strip out more leading directories in the file path. As you'll see later, I ignore this for now and simply clean it up afterward.
• opusenc: This is the actual conversion process. You may want to edit the bitrate to suit your needs. I set mine at 128 but some prefer 160 or higher.

#!/bin/bash
## - The IFS takes care of spaces in file and dirnames
## - your folders may vary
## - what you mount to the folders does not matter
## - in RELDIR, the f5 most likely MUST be edited,
##    since its responsible, how many leading directories
##    will be removed from the directory structure in order
##    to append that exact path to the outfile
## - the commented echos are still in place in order to give
##    you the variables for testing, before running.

IFS=$'\n'

## the paths given here contain the directory structure that I want to keep
## source=/mnt/music/archives/ARTIST/ALBUM/FLACFILE.flac
## local=/mnt/music/library/ARTIST/ALBUM/OPUSFILE.opus

source=/mnt/music/archives
dest=/mnt/music/library

for i in $(find $source -type f -iname '*.flac' );
do
## SET VARIABLES for PATHS and FILENAMES
        fullfile=$i
        filename="${i##*/}"
        filename="${filename%.*}.opus"
        fulldir=$(dirname "${i}")
        reldir="$(echo $fulldir | cut -d'/' -f5-)"
        reldir=${reldir//flac}
        outdir="$dest/$reldir"
        outfile="$outdir/$filename"

# is that working?
# outfile='$local/""$(echo $(dirname "${i}") | cut -d'/' -f5-)"//flac"/"${i##*/}"'
#       echo 'output file: ' "$outfile"

## SHOW ME THE CONTENTS of the VARIABLES
#       echo 'File found:' "$i"
#       echo 'Relative dir: ' "$reldir"
#       echo 'directory will be created: ' "$outdir"
#       echo 'Filename: ' "$filename"
#       echo 'FileExt: ' "$extension"
#       echo 'output file: ' "$outfile"

echo "\n\n"

## CREATE Output Folders
        mkdir -p "$outdir"

## RUN
# ffmpeg and avconv are alternative options if opusenc isn't adequate
opusenc --vbr --bitrate 128 --date "$DATE" \
--title "$TITLE" --artist "$ARTIST" --album "$ALBUM" --genre "$GENRE" \
--comment "ALBUMARTIST=$ALBUMARTIST" --comment "DISCNUMBER=$DISCNUMBER" \
--comment "TRACKNUMBER=$TRACKNUMBER" --comment "TRACKTOTAL=$TRACKTOTAL" \
--comment "LYRICS=$LYRICS" "$fullfile" "$outfile"


## just for testing
#        sleep 1
done

Once you're done, simply save the file and exit your editor. Don't forget to enable execution of the script:

chmod +x transform.sh

Finally, you may now run the script:

./transform.sh

If you used opusenc, you'll see the conversions happen within the terminal as it progresses. You will also see variables printed if you uncommented any of the bash script's comments.

Cleanup

As I noted above, I didn't customize my reldir variable in the script, which caused my output directory to be /mnt/music/library/archives instead of /mnt/music/library. So, I moved the output up one level and deleted the accidental directory.

cd /mnt/music/library
mv archives/** .
rm -rf archives

Check the Resulting Size

If you want to see what kind of file size savings you've gained, you can always use the du command to check:

cd /mnt/music
du -h --max-depth=1 .

In my case, my small library went from 78GB to 6.3GB!

78G    ./archives
6.3G   ./library