#+title: Recursive Command-Line FLAC to Opus Conversion
#+date:  2022-07-30

** Converting FLAC to OPUS
:PROPERTIES:
:CUSTOM_ID: converting-flac-to-opus
:END:
I am currently rebuilding my music library from scratch so that I can
effectively archive all the music I own in the
[[https://en.wikipedia.org/wiki/FLAC][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
[[https://en.wikipedia.org/wiki/Opus_(audio_format)][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
:PROPERTIES:
:CUSTOM_ID: dependencies
:END:
The process I follow utilizes the =opus-tools= package in Ubuntu. Before
proceeding, install the package:

#+begin_src sh
sudo apt install opus-tools
#+end_src

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

*** Conversion Process
:PROPERTIES:
:CUSTOM_ID: conversion-process
:END:
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.

#+begin_src sh
cd ~ && nano transform.sh
#+end_src

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.

#+begin_src sh
#!/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
#+end_src

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

#+begin_src sh
chmod +x transform.sh
#+end_src

Finally, you may now run the script:

#+begin_src sh
./transform.sh
#+end_src

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
:PROPERTIES:
:CUSTOM_ID: cleanup
:END:
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.

#+begin_src sh
cd /mnt/music/library
mv archives/* .
rm -rf archives
#+end_src

*** Check the Resulting Size
:PROPERTIES:
:CUSTOM_ID: check-the-resulting-size
:END:
If you want to see what kind of file size savings you've gained, you can
always use the =du= command to check:

#+begin_src sh
cd /mnt/music
du -h --max-depth=1 .
#+end_src

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

#+begin_src txt
78G    ./archives
6.3G   ./library
#+end_src