add auracast doc

docs/mkdocs/src/apps_and_tools/auracast.md

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+AURACAST TOOL
+=============
+
+The "auracast" tool implements commands that implement broadcasting, receiving
+and controlling LE Audio broadcasts.
+
+=== "Running as an installed package"
+    ```
+    $ bumble-auracast
+    ```
+
+=== "Running from source"
+    ```
+    $ python3 apps/auracast.py <args>
+    ```
+
+# Python Dependencies
+Try installing the optional `[auracast]` dependencies:
+
+=== "From source"
+    ```bash
+    $ python3 -m pip install ".[auracast]"
+    ```
+
+=== "From PyPI"
+    ```bash
+    $ python3 -m pip install "bumble[auracast]"
+    ```
+
+## LC3
+The `auracast` app depends on the `lc3` python module, which is available
+either as PyPI module (currently only available for Linux x86_64).
+When installing Bumble with the optional `auracast` dependency, the `lc3`
+module will be installed from the `lc3py` PyPI package if available.
+If not, you will need to install it separately. This can be done with:
+```bash
+$ python3 -m pip install "git+https://github.com/google/liblc3.git"
+```
+
+## SoundDevice
+The `sounddevice` module is required for audio output to the host's sound
+output device(s) and/or input from the host's input device(s).
+If not installed, the `auracast` app is still functional, but will be limited
+to non-device inputs and output (files, external processes, ...)
+
+On macOS and Windows, the `sounddevice` module gets installed with the
+native PortAudio libraries included.
+
+For Linux, however, PortAudio must be installed separately.
+This is typically done with a command like:
+```bash
+$ sudo apt install libportaudio2
+```
+
+Visit the [sounddevice documentation](https://python-sounddevice.readthedocs.io/)
+for details.
+
+
+# General Usage
+```
+Usage: bumble-auracast [OPTIONS] COMMAND [ARGS]...
+
+Options:
+  --help  Show this message and exit.
+
+Commands:
+  assist    Scan for broadcasts on behalf of an audio server
+  pair      Pair with an audio server
+  receive   Receive a broadcast source
+  scan      Scan for public broadcasts
+  transmit  Transmit a broadcast source
+```
+
+Use `bumble-auracast <command> --help` to get more detailed usage information
+for a specific `<command>`.
+
+## `assist`
+Act as a broadcast assistant.
+
+Use `bumble-auracast assist --help` for details on the commands and options.
+
+The assistant commands are:
+
+### `monitor-state`
+Subscribe to the state characteristic and monitor changes.
+
+### `add-source`
+Add a broadcast source. This will instruct the device to start
+receiving a broadcast.
+
+### `modify-source`
+Modify a broadcast source.
+
+### `remove-source`
+Remote a broadcast source.
+
+## `pair`
+Pair with a device.
+
+## `receive`
+Receive a broadcast source.
+
+The `--output` option specifies where to send the decoded audio samples.
+The following outputs are supported:
+
+### Sound Device
+The `--output` argument is either `device`, to send the audio to the hosts's default sound device, or `device:<DEVICE_ID>` where `<DEVICE_ID>`
+is the integer ID of one of the available sound devices.
+When invoked with `--output "device:?"`, a list of available devices and
+their IDs is printed out.
+
+### Standard Output
+With `--output stdout`, the decoded audio samples are written to the
+standard output (currently always as float32 PCM samples)
+
+### FFPlay
+With `--output ffplay`, the decoded audio samples are piped to `ffplay`
+in a child process. This option is only available if `ffplay` is a command that is available on the host.
+
+### File
+With `--output <filename>` or `--output file:<filename>`, the decoded audio
+samples are written to a file (currently always as float32 PCM)
+
+## `transmit`
+Broadcast an audio source as a transmitter.
+
+The `--input` and `--input-format` options specify what audio input
+source to transmit.
+The following inputs are supported:
+
+### Sound Device
+The `--input` argument is either `device`, to use the host's default sound
+device (typically a builtin microphone), or `device:<DEVICE_ID>` where
+`<DEVICE_ID>` is the integer ID of one of the available sound devices.
+When invoked with `--input "device:?"`, a list of available devices and their
+IDs is printed out.
+
+### Standard Input
+With `--input stdout`, the audio samples are read from the standard input.
+(currently always as int16 PCM).
+
+### File
+With `--input <filename>` or `--input file:<filename>`, the audio samples
+are read from a .wav or raw PCM file.
+
+Use the `--input-format <FORMAT>` option to specify the format of the audio
+samples in raw PCM files. `<FORMAT>` is expressed as:
+`<sample-type>,<sample-rate>,<channels>`
+(the only supported <sample-type> currently is 'int16le' for 16 bit signed integers with little-endian byte order)
+
+## `scan`
+Scan for public broadcasts.
+
+A live display of the available broadcasts is displayed continuously.
+
+# Compatibility With Some Products
+The `auracast` app has been tested for compatibility with a few products.
+The list is still very limited. Please let us know if there are products
+that are not working well, or if there are specific instructions that should
+be shared to allow better compatibiity with certain products.
+
+## Transmitters
+
+The `receive` command has been tested to successfully receive broadcasts from
+the following transmitters:
+
+  * JBL GO 4
+  * Flairmesh FlooGoo FMA120
+  * Eppfun AK3040Pro Max
+  * HIGHGAZE BA-25T
+  * Nexum Audio VOCE and USB dongle
+
+## Receivers
+
+### Pixel Buds Pro 2
+
+The Pixel Buds Pro 2 can be used as a broadcast receiver, controlled by the
+`auracast assist` command, instructing the buds to receive a broadcast.
+
+Use the `assist --command add-source` command to tell the buds to receive a
+broadcast.
+
+Use the `assist --command monitor-state` command to monitor the current sync/receive
+state of the buds.
+
+### JBL
+The JBL GO 4 and other JBL products that support the Auracast feature can be used
+as transmitters or receivers.
+
+When running in receiver mode (pressing the Auracast button while not already playing),
+the JBL speaker will scan for broadcast advertisements with a specific manufacturer data.
+Use the `--manufacturer-data` option of the `transmit` command in order to include data
+that will let the speaker recognize the broadcast as a compatible source.
+
+The manufacturer ID for JBL is 87.
+Using an option like `--manufacturer-data 87:00000000000000000000000000000000dffd` should work (tested on the
+JBL GO 4. The `dffd` value at the end of the payload may be different on other models?).
+
+
+### Others
+
+  * Nexum Audio VOCE and USB dongle