Author here. The real motivation: I've been a Rockbox fan since 2010, when I installed it on my iPod and it completely changed what that device could do. The UI, the codec support, the sheer hackability, nothing else has come close since.

I've wanted that same experience on my desktop for years. So I'm basically trying to bring Rockbox to macOS and Linux as a daemon I can use every day, with MPD-style control on top.

they're at different layers. libmpv is a full media player: demuxing, decoding (via FFmpeg), DSP, output. cpal is just a thin cross-platform PCM sink on top of CoreAudio/ALSA/WASAPI/etc.

Rockbox already brings its own decoders (20+ codecs), its own DSP chain (crossfeed, EQ, replaygain, gapless), and its own mixer. I just need the host OS to accept PCM frames. cpal is the minimal portable shim for that; pulling in libmpv would mean discarding Rockbox's audio pipeline and replacing it with FFmpeg's, which would basically defeat the point of building on Rockbox firmware.

If you spend a lot of time in the shell and are used to manipulating text via chains of piped Unix utilities, then MPD controlled by mpc lets you put music on without leaving that environment that is comfortable and efficient. For example, play album X but not tracks Y or Z from it that I think suck. Or play such-and-such a piece of classical music but in the recording by that particular conductor and ensemble, etc.

EDIT: The below is completely wrong, ignore.

<del>The server-client model means you can run the server (MPD, Rockbox Zig, whatever) on your homelab, and stream music to multiple clients. So you don't have to copy all your music onto your phone, you can just run an MPD client like M.A.L.P. and it will stream from the files on your server. Then there's just one copy of your music collection, tags, etc.: no more keeping tags up-to-date between the copies on your home server, your laptop, your phone... (Do make sure your files are backed up, of course).<del>

Our IT department has a machine called jukebox hooked up to a sound system. Since it runs a music player daemon everybody in the IT department can control the jukebox from their own frontend, phone or whatever.

Technically you could achieve the same with a web frontend, but then you're limited to that UI. A music player daemon is agnostic to the UI, meaning there can be different UIs or you can add music via command line, text interfaces etc.

> Rockbox Zig exposes the full Rockbox audio engine — gapless playback, DSP, 20+ codecs, tag database — through gRPC, GraphQL, HTTP, and MPD APIs

I like having the music player be separate from the client that controls it. I'm currently listening to music on my home desktop PC while using my work laptop, and I can control the music playback from the work laptop by just connecting to the daemon.

You can also use multiple clients if you want. Some TUI, some graphical, some utility like mpdscrobble (that just watches what you listen to and scrobbles it to Last.fm).