# AirPlay

A pure-Elixir **AirPlay (RAOP) audio sender**. Discover receivers on your network
and stream lossless audio to them — no native dependencies, just the Erlang/OTP.
`:crypto`, `:gen_udp` and `:gen_tcp`.

It speaks classic **AirPlay 1 / RAOP**: unencrypted ALAC over RTP with the
NTP-style timing/sync receivers require. Verified streaming real audio to
shairport-sync, AirPort Express, and Apple **HomePods**.

> Experimental AirPlay 2 building blocks (transient SRP pairing,
> ChaCha20-Poly1305 encrypted control channel, binary plist, SETUP) live under
> `AirPlay.V2`. The control plane is verified against real HomePods, but audio
> rendering (PTP clock-slaving) is not complete yet — use the AirPlay 1 API below
> for playback.

This is still WIP, created to scratch an itch.

## Installation

```elixir
def deps do
  [{:airplay, "~> 0.1.0"}]
end
```

## Usage

```elixir
# Discover receivers (mDNS browse of _raop._tcp.local)
AirPlay.discover()
#=> [%{name: "Office", host: "172.16.42.35", port: 7000}, ...]

# Stream a file (decoded to PCM via ffmpeg) at 40% volume
{:ok, session} = AirPlay.play("172.16.42.35", "/music/track.flac", volume: 40)
AirPlay.set_volume(session, 25)
AirPlay.stop(session)

# Or stream raw PCM you already have (44.1 kHz, signed 16-bit LE, stereo, interleaved)
{:ok, session} = AirPlay.play_pcm("172.16.42.35", pcm, volume: 40)
```

A `session` is a lightweight GenServer that streams in the background and stops
itself when the track ends; pass it to `set_volume/2` and `stop/1`.

## Requirements

- Elixir ~> 1.14
- `ffmpeg` on the `PATH` — **only** for `AirPlay.play/3` (file decoding).
  `AirPlay.play_pcm/3` has no external dependency.

## How it works

`play/3` opens an RTSP control connection (`OPTIONS → ANNOUNCE → SETUP → RECORD`),
binds the UDP timing/control ports and answers the receiver's NTP timing probe
*before* `SETUP` (HomePods return `520 Origin Error` otherwise), then paces ALAC
RTP packets to the receiver against a wall-clock with periodic sync packets.

| Module | Role |
| --- | --- |
| `AirPlay.Discovery` | mDNS `_raop._tcp` browse |
| `AirPlay.Rtsp` / `AirPlay.Session` | RTSP control plane + handshake |
| `AirPlay.Player` | RTP audio streaming + timing/sync |
| `AirPlay.Rtp` / `AirPlay.Alac` / `AirPlay.Ntp` | packet builders + codecs |
| `AirPlay.Source` | file → PCM (ffmpeg) + framing |
| `AirPlay.Cast` | play/stop/volume session GenServer |

## License

BSD-3-Clause. See [LICENSE](LICENSE).