This is a script to convert all flac files in a given directory to ogg/opus. I wrote this because mp3 kinda sucks and opus is a free format that is pretty much taking over the internet.

flac2opus

#!/bin/bash

# Copyright 2017 Keefer Rourke <mail@krourke.org>
#
# Permission to use, copy, modify, and/or distribute this software for any
# purpose with or without fee is hereby granted, provided that the above
# copyright notice and this permission notice appear in all copies.
#
# THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCNUMBERLAIMS ALL WARRANTIES WITH
# REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF MERCHANTABILITY
# AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY SPECIAL, DIRECT,
# INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES WHATSOEVER RESULTING FROM
# LOSS OF USE, DATA OR PROFITS, WHETHER IN AN ACTION OF CONTRACT, NEGLIGENCE OR
# OTHER TORTIOUS ACTION, ARISING OUT OF OR IN CONNECTION WITH THE USE OR
# PERFORMANCE OF THIS SOFTWARE.

# usage: flac2opus PATH [-bBITRATE]

which metaflac
if [ $? -ne 0 ]; then
    echo "flac tools are not installed. Run \`sudo dnf install flac\` and try again."
    exit 1
fi
which opusenc
if [ $? -ne 0 ]; then
    echo "opus-tools is not installed. Run \`sudo dnf install opus-tools\` and try again"
    exit 1
fi

# "global" variables
wd="$PWD"
br=256
artfile="$1/.tempart.img"
cleanup=0
hasart=0

# cleanup actions
cleanup() {
    if [ -f "$artfile" ]; then
        rm "$artfile"
    fi
}

# check script usage
[ -z "$1" ] && echo "File path is required." && exit 2;

# parse args
if [ ! -z "$2" ] && [ "${2:0:2}" == "-b" ]; then
    br="$(sed 's/[^0-9]//g' <<< $2)"
fi

# parse each flac file in the specified directory and output to opus format
for f in "$1"/*.flac; do
    # give output correct extension
    basefilename=${f##*/}

    # export metadata; I don't necessarily trust or want every single tag in
    # the exported file, so let's grab the relevant tags and make opus ignore
    # extraneous data
    TITLE=$(metaflac "$f" --show-tag=TITLE | sed s/.*=//g)
    ARTIST=$(metaflac "$f" --show-tag=ARTIST | sed s/.*=//g)
    ALBUMARTIST=$(metaflac "$f" --show-tag=ALBUMARTIST | sed s/.*=//g)
    ALBUM=$(metaflac "$f" --show-tag=ALBUM | sed s/.*=//g)
    DATE=$(metaflac  "$f" --show-tag=DATE | sed s/.*=//g)
    GENRE=$(metaflac "$f" --show-tag=GENRE | sed s/.*=//g)
    DISCNUMBER=$(metaflac "$f" --show-tag=DISCNUMBER | sed s/.*=//g)
    TRACKNUMBER=$(metaflac "$f" --show-tag=TRACKNUMBER | sed s/.*=//g)
    TRACKTOTAL=$(metaflac "$f" --show-tag=TRACKTOTAL | sed s/.*=//g)
    LYRICS=$(metaflac "$f" --show-tag=LYRICS | sed s/.*=//g)
    
    # for the curious I suppose
    #metaflac "$f" --export-tags-to=-

    # if we don't already have an art file, let's try to extract one from the
    # current flac file
    if [ $hasart -eq 0 ]; then
        metaflac "$f" --export-picture-to="$artfile"
        hasart=1
        cleanup=1
    fi

    # convert flac via opusenc and tag the new file; pictures should be copied
    # automagically
    opusenc --vbr --bitrate "$br" --discard-comments --date "$DATE" \
    --title "$TITLE" --artist "$ARTIST" --album "$ALBUM" --genre "$GENRE" \
    --comment "ALBUMARTIST=$ALBUMARTIST" --comment "DISCNUMBER=$DISCNUMBER" \
    --comment "TRACKNUMBER=$TRACKNUMBER" --comment "TRACKTOTAL=$TRACKTOTAL" \
    --comment "LYRICS=$LYRICS" \
    "$f" "$wd/${basefilename/%flac/opus}"

    # cleanup and exit if failure
    if [ $? -ne 0 ]; then
        cleanup
        exit 1
    fi
done

# move the temp artfile to destination with meaningful extension
if [ -f "$artfile" ]; then
    mime=$(file -b --mime-type "$artfile" | sed 's/.*\///g')
    cp "$artfile" "$wd/front.$mime"
fi

cleanup
exit 0

What does this do?

This script will re-encode FLAC files found in the supplied directory to VBR OPUS and output to the directory from which the script was run.

Usage

flac2opus /path/to/directory [-b<target bitrate>]

where target bitrate is the average bitrate of the file; the higher the number the bigger the file.

A default target bitrate of 256kbps is used since this is probably close to transparent with FLAC, though 128kbps would probably be more than enough.

FAQ

Don't you know that opusenc copies metadata automagically?!

... Yes, I am aware that when converting from FLAC to OPUS via opusenc, metadata and images are normally automatically copied, however often the information in many of these comment tags is pretty well useless or populated with annoying information, so this script only writes tags that are useful to most music players.

Will this script ever be updated?

I mean... maybe? Suggestions and edits are welcome. This works for my use cases though, so I won't really put much more time into this — hence the Gist and not a proper repo.

Update: [23:17 04 November 2018] Turns out I made a mistake before and thought that metaflac would re-encode tagged image data to the suitable format for the specified output. Obviously this wasn't the case so this script output badly named images which wouldn't open in some viewers.

The new version of this script now uses file to determine the mimetype of the image, and uses that to provide a better file extension. file --extension (which is supposed to list valid file extensions) was giving me garbage output so I hacked in a solution that works for jpg and png files at the very least... Really you shouldn't be tagging your music with other image formats though 😉

Hey! This is an amazing script!
Here's one issue:
When you use --discard-comments , opusenc even discards the album-art (you can verify it by mediainfo's text view on the .opus file ).
I didnt notice that because VLC stores a cache of artworks.
Though this can be easily fixed by passing --picture "$artfile" the problem arises when the flac files have multiple artwork files (front cover, back cover etc ) , so only one of the artwork gets copied.

Also, if you remove the --discard-comments , and keep the rest, opusenc will not overwrite the values, instead it duplicates them :/
So either I have to stick with 1 artwork or remove all the flags from the script :/

Here's my fork of your script.
I have
Added a -p parameter to manually specify a cover image in case the flac doesn't have it (or you want to change it).

@DroidFreak32 thanks for the comments! I'm glad you found the script useful and were able to make improvements 😄

DISCNUMBERLAIMS Whoops?

I had trouble getting album art embedded within resulting opus with this. After trying multiple times, I now just use Strawberry to convert stuff, and it works just as expected.

Not as convenient as firing up a script, but a very close second.

DISCNUMBERLAIMS Whoops?

Whoops indeed :) Good old search/replace got me I guess :P

Nice but why not use ffmpeg?