AirPlay 2

Shairport Sync offers limited AirPlay 2 support for audio sources on iOS devices, Macs, HomePod minis and Apple TVs. It does not work for iTunes on Windows.

The focus of the development effort has been on getting good audio performance for iOS and Mac. Features outside this focus may be missing or broken. So, for example, remote control doesn't work.

For AirPlay 2, Shairport Sync uses another application called nqptp ("Not Quite PTP") for timing and synchronisation. nqptp must run as root and must have exclusive access to ports 319 and 320.

AirPlay 2 functionality is available on recent Linux and FreeBSD builds. The FreeBSD implementation has not been extensively tested. OpenBSD and Cygwin are not supported.

The AirPlay 2 version of Shairport Sync will not work if installed on macOS. This is because nqptp uses ports 319 and 320 but these ports are unavailable because there are used by macOS to support its implementation of AirPlay 2.

The AirPlay 2 build requires a good deal of extra library support and may not fit into smaller devices. It also requires more CPU power and more RAM.

What Works

AirPlay 2 for iOS, HomePod mini, AppleTV and Mac players.

What Does Not Work

No Remote Control
No AirPlay 2 for Windows iTunes

What Partly Works

Lossless or High Definition Lossless material over AirPlay 2 is automatically transcoded to ALAC or AAC before sending it via AirPlay 2 to Shairport Sync.

Limitations

Only a single instance of Shairport Sync can run on a device.
The AirPlay 2 version of Shairport Sync will not work if installed on macOS, since nqptp can not be installed on macOS.

AirPlay 2 -- What You Need

AirPlay 2 support needs a more powerful CPU for decoding and synchronisation and more memory for bigger buffers and larger libraries. Raspberry Pi OS, Ubuntu 20.04 on a VM and Ubuntu 20.04.2 64-bit Server Edition have been used extensively in development, with Alpine Linux and FreeBSD 12.2 being used to a lesser extent.

So, here are some guideline requirements:

Full access, including root privileges, to a system at least as powerful as a Raspberry Pi 2.
A fully up-to-date Linux. This is important, as some of the libraries must be the latest available.
An audio output, for example an alsa device (or sndio in FreeBSD). The stdout and pipe backends continue to work as before. Other backends have not been tested.

Guides

To build Shairport Sync for AirPlay 2 on Linux, please follow the guide at BUILDFORAP2.md.
A guide for building on FreeBSD is forthcoming.

AirPlay 2 -- More About What Works

Two types of audio are received by Shairport Sync -- "Realtime" streams of CD quality ALAC (like AirPlay 1) and "Buffered Audio" streams of AAC stereo at 44,100 frames per second. The selection of stream type is made by the player.
Audio is synchronised with other AirPlay 2 devices, including AirPlay 2 devices that have their own master clocks.
Shairport Sync continues to support AirPlay 1, and offers an AirPlay 1 compatibility mode for situations where iTunes on macOS or macOS Music plays to multiple speakers and one of more of them is compatible with AirPlay 1 only.

Acknowledgements

Huge thanks are due to a number of individuals who made direct and valuable contributions to Shairport Sync:

ejurgensen contributed ideas and code. The pair_ap submodule and related code in rtsp.c is theirs.
JD Smith contributed ideas, comments and suggestions along with extensive and thorough testing.
Charles Omer contributed ideas, comments, bug fixes, documentation and Docker automation (forthcoming).
ckdo for their pathfinding work on AirPlay 2, especially the HomeKit pairing.

Much of Shairport Sync's AirPlay 2 functionality is based on ideas developed at the openairplay airplay2-receiver repository. It is a pleasure to acknowledge the work of the contributors there.

Finally

Did we mention AirPlay 2 support is experimental?

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