Overview
        --------

mus is a simple CLI client/daemon music player consuming a newline separated plaintext path (files
or directories) playlist. It is formed of several independent parts:
    * mus_daemon:
        Consume the playlist and play its items via mus_player.

    * mus_client:
        Send commands to the player and receive its answers, read or modify the
        playlist.

    * mus_player:
        Play audio files and answer to mus_client's commands. Notable features
        include gapless playback, ReplayGain support and event reporting.
        Format support: FLAC (16 bits), Vorbis and Opus; mono/stereo only

    * mus_album_* and fair_shuf:
        Optional album tools for random but fair album picking. These assume
        that the music directory arborescence is structured so that albums are
        at depth 2.

A lemonbar sh status script can be found at [1] (superseded by [2], though).


        Dependencies and portability
        ----------------------------

In addition to the latest POSIX environment, you'll need the following:
    * GNU11 compiler (gcc or clang) at build time
    * libao
    * libflac, vorbisfile, opusfile (each optional)
    * socat
    * /bin/sh with local/typeset extension (all notable implementations)
    * awk with "/dev/stderr" extension (all notable implementations)
    * xargs -0 and sed -E (GNU, *BSD, MacOS and Illumos; soon in POSIX, cf [3] & [4])
    * flock (util-linux, base or port; cf [5] for other platforms)
    * ed (POSIX requirement, but often missing from GNU/Linux distros)

In brief, at least GNU/Linux, *BSD, MacOS and Illumos should work.


        Building and installation
        -------------------------

To build and install mus (default values shown between brackets):
    $ [CC=gcc] [LTO=false] [NATIVE=false] [USE_FLAC=true] [USE_OGG_VORBIS=false] \
          [USE_OGG_OPUS=false] ./build.sh
    # [DESTDIR=] [PREFIX=/usr/local] ./build.sh install

To install the optional album tools:
    # [DESTDIR=] [PREFIX=/usr/local] ./build.sh albumtools_install

To uninstall:
    # [DESTDIR=] [PREFIX=/usr/local] ./build.sh uninstall
    # [DESTDIR=] [PREFIX=/usr/local] ./build.sh albumtools_uninstall


        Usage examples
        --------------

Launch the server with cat as status notification command:
    $ mus_daemon -s cat [OPTIONS] &

If using the album tools, initialize the database:
    $ mus_album_db_create [MUSIC_DIRECTORY...]

And pick two albums, update the database and append them to the playlist:
    $ mus_album_pick album1/ album2/ | mus_client PL_APPEND

Same as above, without needing the album tools:
    $ readlink -f album1/ album2/ | mus_client PL_APPEND

Append 100 random albums (mus_album_rand implicitely updates the database):
    $ mus_album_rand 100 | mus_client PL_APPEND

Then you can issue commands via mus_client:
    $ mus_client TOGGLE_PLAY_PAUSE
    $ mus_client ALBUM_NEXT
    $ mus_client PL_EDIT
    ...


        Environment variables
        ---------------------

For mus:
    * MUS_SOCKET
        Defaults to /tmp/mus.sock. Useful if you want to run several instances.

    * MUS_PLAYLIST
        Defaults to ${XDG_CONFIG_HOME:-$HOME/.config}/mus/playlist.

    * VISUAL or TERM and EDITOR
        How to edit the playlist with `mus_client PL_EDIT`.

For the album tools:
    * MUS_ALBUM_DB
        Defaults to ${XDG_CONFIG_HOME:-$HOME/.config}/mus/album_db.

    * MUS_MUSIC_DIR
        Defaults to $HOME/Music.


        Troubleshooting
        ---------------

Setting a libao config file can solve some common problems like the
`Unknown PCM cards.pcm.front` message from ALSA:
    $ cat /etc/libao.conf
    # Avoid trying pulseaudio
    default_driver=alsa
    # Avoid problems with front being tried first
    dev=default


[1] https://git.sr.ht/~q3cpma/dotfiles/tree/40862a33735673e47f6dafece545887f7a7040ab/item/.config/lemonbar/mus_status.sh
[2] https://git.sr.ht/~q3cpma/lemonbar-tcl
[3] https://austingroupbugs.net/view.php?id=243
[4] https://austingroupbugs.net/view.php?id=528
[5] https://github.com/discoteq/flock