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Introduction

An open-source implementation of an AirPlay mirroring server for the Raspberry Pi. The goal is to make it run smoothly even on a Raspberry Pi Zero.

State

Screen mirroring and audio works. The GPU is used for decoding the h264 video stream. The Pi has no hardware acceleration for audio (AirPlay uses AAC), so the FDK-AAC decoder is used for that.

Both works fine one a Raspberry Pi 3B+. Unfortunately, it seems the Pi Zero is too slow for decoding audio at a reasonable speed. In order to get audio decoding fast enough for the Pi Zero, we likely have to use a different AAC decoder library.

By using OpenSSL for AES decryption, I was able to speed up the decryption of video packets from up to 0.2 seconds to up to 0.007 seconds for large packets (On the Pi Zero). Average is now more like 0.002 seconds.

If you are seeing long playback pauses, make sure the DUMP flags are not active. Disk IO can slow down the whole program when dumping to files.

There still are some minor issues. Have a look at the TODO list below.

Please note RPiPlay might not be suitable for remote video playback, as it lacks a dedicated component for that: It seems like AirPlay on an AppleTV switches to a standard AirPlay connection when video playback starts, thus avoiding the re-encoding of the video. For details, refer to the inofficial AirPlay specification.

Building

The following packages are required for building on Raspbian:

  • cmake (for the build system)
  • libavahi-compat-libdnssd-dev (for the bonjour registration)
  • libssl-dev (for crypto primitives)
  • iclient and Broadcom's OpenMAX stack as present in /opt/vc in Raspbian.

For building on a fresh Raspbian install, these steps should be run in the project's root folder:

sudo apt-get install cmake
sudo apt-get install libavahi-compat-libdnssd-dev
sudo apt-get install libssl-dev
mkdir build
cd build
cmake ..
make

Usage

Start the airplay_server executable and an AirPlay mirror target device will appear in the network. At the moment, these options are implemented:

-n name: Specify the network name of the AirPlay server

-b: Hide the black background behind the video

-a (hdmi|analog|off): Set audio output device

-v/-h: Displays short help and version information

Authors

The code in this repository accumulated from various sources over time. Here is my attempt at listing the various authors and the components they created:

  • dsafa22: Created an AirPlay 2 mirroring server for Android based on ShairPlay. This project is basically a port of dsafa22's code to the Raspberry Pi, utilizing OpenMAX and OpenSSL for better performance on the Pi. All code in lib/ with a header crediting Administrator is dsafa22's work. License: unknown

  • Juho Vähä-Herttua and contributors: Created an AirPlay audio server called ShairPlay, including support for Fairplay based on PlayFair. Most of the code in lib/ originally stems from this project. License: GNU LGPLv2.1+

  • EstebanKubata: Created a FairPlay library called PlayFair. Located in the lib/playfair folder. License: GNU GPL

  • Jonathan Beck, Nikias Bassen and contributors: Created a library for plist handling called libplist. Located in the lib/plist folder. License: GNU LGPLv2.1+

  • Joyent, Inc and contributors: Created an http library called http-parser. Located at lib/http_parser.(c|h). License: MIT

  • Google, Inc and contributors: Created an implementation of curve 25519 called curve25519-donna. Located in the lib/curve25519 folder. License: 3-Clause BSD

  • Team XBMC: Managed to show a black background for OpenMAX video rendering. This code is used in the video renderer. License: GNU GPL

  • Orson Peters and contributors: An implementation of Ed25519 signatures. Located in lib/ed25519, License: ZLIB; Depends on LibTomCrypt, License: Public Domain

Contributing

I'm not planning to regularly maintain this project. Instead, I'm hoping this project can be improved in a community effort. I'll fix and add as much as I need for personal use, and I count on you to do the same!

Your contributions are more than welcome!

Todo

  • Properly handle timestamps and ntp => Smooth playback, low latency
  • Use OpenSSL for the elliptic curve crypto?
  • Bug: Sometimes cannot be stopped => Likely deadlock in audio time thread