AirPlay

A pure-Elixir AirPlay audio sender. Discover receivers on your network and stream lossless audio to them using Erlang/OTP primitives: :crypto, :gen_udp and :gen_tcp.

It supports 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.

It also has working AirPlay 2 support under AirPlay.V2: transient SRP pairing, ChaCha20-Poly1305 encrypted RTSP, binary plist SETUP/RECORD/FLUSH, PTP timing, encrypted ALAC RTP audio, volume control, periodic /feedback keepalives, and multi-room AirPlay 2 group playback.

Audio is stream-decoded (ffmpeg -re → on-demand frames, audio stream only — embedded cover art is dropped), so playback starts after a short prebuffer instead of decoding the whole file up front, and a multi-hour source no longer holds its entire PCM in memory.

AirPlay 2 timing uses the receiver's own PTP clock. A HomePod's grandmaster clock runs on its uptime (nowhere near host wall-clock time) and it does not answer Delay_Req, so the offset is taken one-way from each Sync/Follow_Up — RTP sync packets are then stamped in the receiver's clock frame rather than the host's, which is what makes playback work regardless of the host OS or clock.

AirPlay 2 playback also comes in two flavours: one-shot AirPlay.V2.Player / AirPlay.V2.GroupPlayer (pair → set up → stream one file → tear down), and persistent AirPlay.V2.Session / AirPlay.V2.GroupSession that keep the connection and PTP clock warm across tracks — so an album or audiobook changes tracks without re-paying the ~5s pair + SETUP + PTP cold-start each time.

This is still WIP, created to scratch an itch.

Installation

def deps do
  [{:airplay, "~> 0.4.2"}]
end

AirPlay 1 / RAOP usage

# 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.

AirPlay 2 usage

The AirPlay 2 API is lower-level than the RAOP AirPlay.play/3 convenience API and currently lives under AirPlay.V2.

# Play one file to an AirPlay 2 receiver. This call runs until playback finishes.
{:ok, stats} =
  AirPlay.V2.Player.play_file("172.16.42.35", "/music/track.flac",
    volume: 0.4
  )

# Play the same file to an AirPlay 2 receiver group.
{:ok, stats} =
  AirPlay.V2.GroupPlayer.play_file(
    [
      %{host: "172.16.42.35", port: 7000},
      %{host: "172.16.42.62", port: 7000}
    ],
    "/music/track.flac",
    volume: 0.4
  )

For long-running apps, start AirPlay 2 playback in a supervised process or task. AirPlay.V2.Player.set_volume/2, AirPlay.V2.GroupPlayer.set_volume/2, AirPlay.V2.Player.stop/1, and AirPlay.V2.GroupPlayer.stop/1 operate on that running playback process.

Persistent sessions (connection reuse across tracks)

play_file/3 pairs, sets up, runs PTP, streams one file, and tears everything down — fine for a single track, but paying that ~5s cold-start on every track of an album is wasteful. AirPlay.V2.Session (and AirPlay.V2.GroupSession for groups) keep the connection and clock warm so the next track just flushes and streams:

# Connect once (pair → SETUP → RECORD → PTP). Returns a session process.
{:ok, session} = AirPlay.V2.Session.connect("172.16.42.35", owner: self())

# Stream successive files down the same connection. Each call continues the RTP
# timeline (FLUSH with the running seq/timestamp), so there is no re-pair / re-PTP.
AirPlay.V2.Session.play(session, "/music/track-1.flac")
# ... when the track ends the session sends `{AirPlay.V2.Session, :ended, gen}`
# to `owner` and goes idle, keeping the connection alive with FEEDBACK keepalives.
AirPlay.V2.Session.play(session, "/music/track-2.flac")

AirPlay.V2.Session.set_volume(session, 0.4)
AirPlay.V2.Session.stop(session)    # flush current track, stay connected
AirPlay.V2.Session.close(session)   # tear down and release the receiver

The session sends its owner (defaulting to the caller of connect/2):

• {AirPlay.V2.Session, :ended, play_gen} — the current track finished cleanly
• {AirPlay.V2.Session, :error, play_gen, reason} — a track failed to start; the session stays connected and idle

AirPlay.V2.GroupSession has the same API but takes a list of receivers in connect/2 (the first receiver is the PTP primary that drives the shared clock).

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.

License

GNU General Public License v3.0 or later (GPL-3.0-or-later). See LICENSE.