# Configuration

## Sources

Audio sources are added to the server as `source` in the `[stream]` section of the configuration file `/etc/snapserver.conf`. Every source must be fed with a fixed sample format, that can be configured per stream (e.g. `48000:16:2`).  

The following notation is used in this paragraph:

- `<angle brackets>`: the whole expression must be replaced with your specific setting
- `[square brackets]`: the whole expression is optional and can be left out
- `[key=value]`: if you leave this option out, "value" will be the default for "key"

The general format of an audio source is:

```sh
TYPE://host/path?name=<name>[&codec=<codec>][&sampleformat=<sampleformat>][&chunk_ms=<chunk ms>]
```

parameters have the form `key=value`, they are concatenated with an `&` character.
Parameter `name` is mandatory for all sources, while `codec`, `sampleformat` and `chunk_ms` are optional
and will override the default `codec`, `sampleformat` or `chunk_ms` settings.
Non blocking sources support the `dryout_ms` parameter: when no new data is read from the source, send silence to the clients

Available audio source types are:

### pipe

Captures audio from a named pipe

```sh
pipe:///<path/to/pipe>?name=<name>[&mode=create][&dryout_ms=2000]
```

`mode` can be `create` or `read`. Sometimes your audio source might insist in creating the pipe itself. So the pipe creation mode can by changed to "not create, but only read mode", using the `mode` option set to `read`

### librespot

Launches librespot and reads audio from stdout

```sh
librespot:///<path/to/librespot>?name=<name>[&dryout_ms=2000][&username=<my username>&password=<my password>][&devicename=Snapcast][&bitrate=320][&wd_timeout=7800][&volume=100][&onevent=""][&normalize=false][&autoplay=false][&cache=""][&disable_audio_cache=false][&killall=false][&params=extra-params]
```

Note that you need to have the librespot binary on your machine and the sampleformat will be set to `44100:16:2`

#### Available parameters

Parameters used to configure the librespot binary ([see librespot-org options](https://github.com/librespot-org/librespot/wiki/Options)):

- `username`: Username to sign in with
- `password`: Password
- `devicename`: Device name
- `bitrate`: Bitrate (96, 160 or 320). Defaults to 320
- `volume`: Initial volume in %, once connected [0-100]
- `onevent`: The path to a script that gets run when one of librespot's events is triggered
- `normalize`: Enables volume normalisation for librespot
- `autoplay`: Autoplay similar songs when your music ends
- `cache`: Path to a directory where files will be cached
- `disable_audio_cache`: Disable caching of the audio data
- `params`: Optional string appended to the librespot invocation. This allows for arbitrary flags to be passed to librespot, for instance `params=--device-type%20avr`. The value has to be properly URL-encoded.

Parameters introduced by Snapclient:

- `killall`: Kill all running librespot instances before launching librespot
- `wd_timeout`: Restart librespot if it doesn't create log messages for x seconds

### airplay

Launches [shairport-sync](https://github.com/mikebrady/shairport-sync) and reads audio from stdout

```sh
airplay:///<path/to/shairport-sync>?name=<name>[&dryout_ms=2000][&devicename=Snapcast][&port=5000][&password=<my password>]
```

Note that you need to have the shairport-sync binary on your machine and the sampleformat will be set to `44100:16:2`

#### Available parameters

Parameters used to configure the shairport-sync binary:

- `devicename`: Advertised name
- `port`: RTSP listening port
- `password`: Password
- `params`: Optional string appended to the shairport-sync invocation. This allows for arbitrary flags to be passed to shairport-sync, for instance `params=--on-start=start.sh%20--on-stop=stop.sh`. The value has to be properly URL-encoded.

### file

Reads PCM audio from a file

```sh
file:///<path/to/PCM/file>?name=<name>
```

### process

Launches a process and reads audio from stdout

```sh
process:///<path/to/process>?name=<name>[&dryout_ms=2000][&wd_timeout=0][&log_stderr=false][&params=<process arguments>]
```

#### Available parameters

- `wd_timeout`: kill and restart the process if there was no message logged for x seconds to stderr (0 = disabled)
- `log_stderr`: Forward stderr log messages to Snapclient logging
- `params`: Params to start the process with

### tcp server

Receives audio from a TCP socket (acting as server)

```sh
tcp://<listen IP, e.g. 127.0.0.1>:<port>?name=<name>[&mode=server]
```

default for `port` (if omitted) is 4953, default for `mode` is `server`

Mopdiy configuration would look like this (running GStreamer in [client mode](https://www.freedesktop.org/software/gstreamer-sdk/data/docs/latest/gst-plugins-base-plugins-0.10/gst-plugins-base-plugins-tcpclientsink.html))

```sh
[audio]
output = audioresample ! audioconvert ! audio/x-raw,rate=48000,channels=2,format=S16LE ! wavenc ! tcpclientsink
```

### tcp client

Receives audio from a TCP socket (acting as client)

```sh
tcp://<server IP, e.g. 127.0.0.1>:<port>?name=<name>&mode=client
```

Mopdiy configuration would look like this (running GStreamer in [server mode](https://www.freedesktop.org/software/gstreamer-sdk/data/docs/latest/gst-plugins-base-plugins-0.10/gst-plugins-base-plugins-tcpserversink.html)):

```sh
[audio]
output = audioresample ! audioconvert ! audio/x-raw,rate=48000,channels=2,format=S16LE ! wavenc ! tcpserversink
```

### alsa

Captures audio from an alsa device

```sh
alsa://?name=<name>&device=<alsa device>[&send_silence=false][&idle_threshold=100]
```

#### Available parameters

- `device`: alsa device name or identifier, e.g. `default` or `hw:0,0` or `hw:0,0,0`
- `idle_threshold`: switch stream state from playing to idle after receiving `idle_threshold` milliseconds of silence
- `send_silence`: forward silence to clients when stream state is `idle`

The output of any audio player that uses alsa can be redirected to Snapcast by using an alsa loopback device:

1. Setup the alsa loopback device by loading the kernel module:

    ```sh
    sudo modprobe snd-aloop
    ```

    The loopback device can be created during boot by adding `snd-aloop` to `/etc/modules`

2. The loopback device should show up in `aplay -l`

    ```sh
    aplay -l
    **** List of PLAYBACK Hardware Devices ****
    card 0: Loopback [Loopback], device 0: Loopback PCM [Loopback PCM]
    Subdevices: 8/8
    Subdevice #0: subdevice #0
    Subdevice #1: subdevice #1
    Subdevice #2: subdevice #2
    Subdevice #3: subdevice #3
    Subdevice #4: subdevice #4
    Subdevice #5: subdevice #5
    Subdevice #6: subdevice #6
    Subdevice #7: subdevice #7
    card 0: Loopback [Loopback], device 1: Loopback PCM [Loopback PCM]
    Subdevices: 8/8
    Subdevice #0: subdevice #0
    Subdevice #1: subdevice #1
    Subdevice #2: subdevice #2
    Subdevice #3: subdevice #3
    Subdevice #4: subdevice #4
    Subdevice #5: subdevice #5
    Subdevice #6: subdevice #6
    Subdevice #7: subdevice #7
    card 1: Intel [HDA Intel], device 0: CX20561 Analog [CX20561 Analog]
    Subdevices: 1/1
    Subdevice #0: subdevice #0
    card 1: Intel [HDA Intel], device 1: CX20561 Digital [CX20561 Digital]
    Subdevices: 1/1
    Subdevice #0: subdevice #0
    card 2: CODEC [USB Audio CODEC], device 0: USB Audio [USB Audio]
    Subdevices: 0/1
    Subdevice #0: subdevice #0
    ```

    In this example the loopback device is card 0 with devices 0 and 1, each having 8 subdevices.  
    The devices are addressed with `hw:<card idx>,<device idx>,<subdevice num>`, e.g. `hw:0,0,0`.  
    If a process plays audio using `hw:0,0,x`, then the audio will be looped back to `hw:0,1,x`

3. Configure your player to use a loopback device

    For mopidy (gstreamer) in `mopidy.conf`:

    ```sh
    output = audioresample ! audioconvert ! audio/x-raw,rate=48000,channels=2,format=S16LE ! alsasink device=hw:0,0,0
    ```

    For mpd: in `mpd.conf`

    ```sh
    audio_output_format            "48000:16:2"
    audio_output {
            type            "alsa"
            name            "My ALSA Device"
            device          "hw:0,0,0"      # optional
    #       auto_resample   "no"
    #       mixer_type      "hardware"      # optional
    #       mixer_device    "default"       # optional
    #       mixer_control   "PCM"           # optional
    #       mixer_index     "0"             # optional
    }
    ```

4. Configure Snapserver to capture the loopback device:

    ```sh
    [stream]
    source = alsa://?name=SomeName&sampleformat=48000:16:2&device=hw:0,1,0
    ```

### meta

Read and mix audio from other stream sources

```sh
meta:///<name of source#1>/<name of source#2>/.../<name of source#N>?name=<name>
```

Plays audio from the active source with the highest priority, with `source#1` having the highest priority and `source#N` the lowest.  
Use `codec=null` for stream sources that should only serve as input for meta streams
