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# BPD Plugin

BPD is a music player using music from a beets library. It runs as a daemon and implements the MPD protocol, so it’s compatible with all the great MPD clients out there. I’m using Theremin, gmpc, Sonata, and Ario successfully.

## Dependencies

Before you can use BPD, you’ll need the media library called GStreamer (along with its Python bindings) on your system.

- On Mac OS X, you can use Homebrew. Run `brew install gstreamer gst-plugins-base pygobject3`.

- On Linux, you need to install GStreamer 1.0 and the GObject bindings for python. Under Ubuntu, they are called `python-gi` and `gstreamer1.0`.

You will also need the various GStreamer plugin packages to make everything work. See the Chromaprint/Acoustid Plugin documentation for more information on installing GStreamer plugins.

Once you have system dependencies installed, install `beets` with `bpd` extra which installs Python bindings for `GStreamer`:

    pip install "beets[bpd]"

## Usage

To use the `bpd` plugin, first enable it in your configuration (see Using Plugins). Then, you can run BPD by invoking:

    $ beet bpd

Fire up your favorite MPD client to start playing music. The MPD site has a long list of available clients. Here are my favorites:

- Linux: gmpc, Sonata

- Mac: Theremin

- Windows: I don’t know. Get in touch if you have a recommendation.

- iPhone/iPod touch: Rigelian

One nice thing about MPD’s (and thus BPD’s) client-server architecture is that the client can just as easily on a different computer from the server as it can be run locally. Control your music from your laptop (or phone!) while it plays on your headless server box. Rad!

## Configuration

To configure the plugin, make a `bpd:` section in your configuration file. The available options are:

- host: Default: Bind to all interfaces.

- port: Default: 6600

- password: Default: No password.

- volume: Initial volume, as a percentage. Default: 100

- control_port: Port for the internal control socket. Default: 6601

Here’s an example:

    bpd:
        host: 127.0.0.1
        port: 6600
        password: seekrit
        volume: 100

## Implementation Notes

In the real MPD, the user can browse a music directory as it appears on disk. In beets, we like to abstract away from the directory structure. Therefore, BPD creates a “virtual” directory structure (artist/album/track) to present to clients. This is static for now and cannot be reconfigured like the real on-disk directory structure can. (Note that an obvious solution to this is just string matching on items’ destination, but this requires examining the entire library Python-side for every query.)

BPD plays music using GStreamer’s `playbin` player, which has a simple API but doesn’t support many advanced playback features.

## Differences from the real MPD

BPD currently supports version 0.16 of the MPD protocol, but several of the commands and features are “pretend” implementations or have slightly different behaviour to their MPD equivalents. BPD aims to look enough like MPD that it can interact with the ecosystem of clients, but doesn’t try to be a fully-fledged MPD replacement in terms of its playback capabilities.

These are some of the known differences between BPD and MPD:

- BPD doesn’t currently support versioned playlists. Many clients, however, use plchanges instead of playlistinfo to get the current playlist, so plchanges contains a dummy implementation that just calls playlistinfo.

- Stored playlists aren’t supported (BPD understands the commands though).

- The `stats` command always send zero for `playtime`, which is supposed to indicate the amount of time the server has spent playing music. BPD doesn’t currently keep track of this.

- The `update` command regenerates the directory tree from the beets database synchronously, whereas MPD does this in the background.

- Advanced playback features like cross-fade, ReplayGain and MixRamp are not supported due to BPD’s simple audio player backend.

- Advanced query syntax is not currently supported.

- Clients can’t use the `tagtypes` mask to hide fields.

- BPD’s `random` mode is not deterministic and doesn’t support priorities.

- Mounts and streams are not supported. BPD can only play files from disk.

- Stickers are not supported (although this is basically a flexattr in beets nomenclature so this is feasible to add).

- There is only a single password, and is enabled it grants access to all features rather than having permissions-based granularity.

- Partitions and alternative outputs are not supported; BPD can only play one song at a time.

- Client channels are not implemented.