VIDEOS

Antimof/UxPlay: AirPlay Unix mirroring server

Jan 7, 2022

This project is a GPLv3 open source unix AirPlay2 Mirror server for Linux, macOS, and *BSD. It is now hosted at the github site https://github.com/FDH2/UxPlay (where development and user-assistance now takes place), although it initially was developed by antimof using code from RPiPlay, which in turn derives from AirplayServer, shairplay, and playfair. (The antimof site is mainly inactive, but periodically posts updates pulled from the main UxPlay site).

Its main use is to act like an AppleTV for screen-mirroring (with audio) of iOS/iPadOS/macOS clients (iPhones, iPads, MacBooks) in a window on the server display (with the possibility of sharing that window on screen-sharing applications such as Zoom) on a host running Linux, macOS, or other unix. UxPlay supports a "legacy" form of Apple's AirPlay Mirror protocol introduced in iOS 12; client devices running iOS/iPadOS 12 or later are supported, as is a (nonfree) Windows-based AirPlay-client software emulator, AirMyPC. Older (32-bit) client devices that can only run iOS 9.3 or iOS 10.3 are currently partially supported by UxPlay: reports indicate that screen-mirroring video works, audio is a work in progess. (Details of what is publically known about Apple's AirPlay2 protocol can be found here and here).

The UxPlay server and its client must be on the same local area network, on which a Bonjour/Zeroconf mDNS/DNS-SD server is also running (only DNS-SD "Service Discovery" service is strictly necessary, it is not necessary that the local network also be of the ".local" mDNS-based type). On Linux and BSD Unix servers, this is usually provided by Avahi, through the avahi-daemon service, and is included in most Linux distributions (this service can also be provided by macOS, iOS or Windows servers).

Connections to the UxPlay server by iOS/MacOS clients can be initiated both in AirPlay Mirror mode (which streams lossily-compressed AAC audio while mirroring the client screen, or in the alternative AirPlay Audio mode which streams Apple Lossless (ALAC) audio without screen mirroring (the accompanying metadata and cover art in this mode is not displayed). Switching between these two modes during an active connection is possible: in Mirror mode, close the mirror window and start an Audio mode connection, switch back by initiating a Mirror mode connection. Note that Apple DRM (as in Apple TV app content on the client) cannot be decrypted by UxPlay, and (unlike with a true AppleTV), the client cannot run a http connection on the server instead of streaming content from one on the client.

UxPlay uses GStreamer Plugins for rendering audio and video, and does not offer the alternative Raspberry-Pi-specific audio and video renderers available in RPiPlay. It is tested on a number of systems, including (among others) Debian 11.2, Ubuntu 20.04 and 21.10, Linux Mint 20.2, OpenSUSE 15.3, macOS 10.15.7, FreeBSD 13.0.

Using Gstreamer means that video and audio are supported "out of the box", using a choice of plugins. Gstreamer decoding is plugin agnostic, and uses accelerated decoders if available. For Intel integrated graphics, the VAAPI plugin is preferable, (but don't use it with nVidia).

Note to packagers: OpenSSL-3.0.0 solves GPL v3 license issues.

Some Linux distributions such as Debian do not allow distribution of compiled GPL code linked to OpenSSL-1.1.1 because its "dual OpenSSL/SSLeay" license has some incompatibilites with GPL, unless all code authors have explicitly given an "exception" to allow such linking (the historical origins of UxPlay make this impossible to obtain). Other distributions treat OpenSSL as a "System Library" which the GPL allows linking to.

For "GPL-strict" distributions, UxPlay can be built using OpenSSL- 3.0.0, which has a new GPLv3-compatible license.

Either download and unzip UxPlay-master.zip, or (if git is installed): "git clone https://github.com/FDH2/UxPlay".

*This is also a pull request on the original site https://github.com/antimof/UxPlay ; that original project is inactive, but the pull request with changes up to 2021-12-10 were recently merged with the antimof tree (thank you antimof!).

Building UxPlay on Linux (or *BSD):

(Instructions for Debian/Ubuntu; adapt these for other Linuxes; for macOS, see below).

You need a C/C++ compiler (e.g. g++) with the standard development libraries installed.

Make sure that cmake=3.4.1 and pkg-config are also installed: "sudo apt-get install cmake pkg-config". In a terminal window, change directories to the source directory of the downloaded source code ("UxPlay-master" for zipfile downloads, "UxPlay" for "git clone" downloads), then do

  1. sudo apt-get install libssl-dev libplist-dev libavahi-compat-libdnssd-dev libgstreamer1.0-dev libgstreamer-plugins-base1.0-dev gstreamer1.0-libav gstreamer1.0-plugins-bad
  2. sudo apt-get install gstreamer1.0-vaapi (For hardware-accelerated Intel graphics, but not nVidia graphics)
  3. sudo apt-get install libx11-dev (for the "ZOOMFIX" X11_display name fix for screen-sharing with e.g., ZOOM)
  4. cmake . (or "cmake -DZOOMFIX=ON ." to get a screen-sharing fix to make X11 mirror display windows visible to screen-sharing applications such as Zoom, see below).
  5. make
  6. sudo make install (you can afterwards uninstall with sudo make uninstall in the same directory in which this was run)

If you intend to modify the code, use a separate "build" directory: replace "cmake [ ] . " by "mkdir build ; cd build ; cmake [ ] .."; you can then clean the build directory with "rm -rf build/* " (run from within the UxPlay source directory) without affecting the source directories which contain your modifications.

The above script installs the executable file "uxplay" to /usr/local/bin, (and installs a manpage to somewhere like /usr/local/share/man/man1 and README files to somewhere like /usr/local/share/doc/uxplay). It can also be found in the build directory after the build processs. Run uxplay in a terminal window.

Note libplist-dev (version 2.0 or greater) is a new dependency (the original antimof version UxPlay-1.2 supplied it). Older Linux distributions may only supply libplist 1.x, which is too old. [Installing libplist-dev (with libplist3) from ubuntu 18.04 solves this problem on ubuntu 16.04.] If you cannot find a libplist-2.x package that installs on your older distribution, you can get it at https://github.com/libimobiledevice/libplist and build it from source. (You will need build tools autoconf, automake, libtool, and may need to also install some libpython*-dev package). By default, libplist installs in /usr/local/lib. If this is not in the library path (as in ubuntu), create a file /etc/ld.so.conf.d/libplist.conf containing the text "/usr/local/lib", and run "sudo ldconfig" to permanently add /usr/local/lib to the library path.

Red Hat, Fedora, CentOS: (sudo yum install) openssl-devel libplist-devel avahi-compat-libdns_sd-devel (+libX11-devel for ZOOMFIX). The required GStreamer packages are: gstreamer1-devel gstreamer1-plugins-base-devel gstreamer1-libav gstreamer1-plugins-bad-free ( + gstreamer1-vaapi for intel graphics).

OpenSUSE: (sudo zypper install) libopenssl-devel libplist-devel avahi-compat-mDNSResponder-devel (+ libX11-devel for ZOOMFIX). The required GStreamer packages are: gstreamer-devel gstreamer-plugins-base-devel gstreamer-plugins-libav gstreamer-plugins-bad (+ gstreamer-plugins-vaapi for Intel graphics).

FreeBSD: (sudo pkg install) libplist gstreamer1, gstreamer1-libav, gstreamer1-plugins, gstreamer1-plugins-* (* = core, good, bad, x, gtk, gl, vulkan, pulse ...), (+ gstreamer1-vaapi for Intel graphics). Either avahi-libdns or mDNSResponder must also be installed to provide the dns_sd library. OpenSSL is already installed as a System Library. "ZOOMFIX" is untested; don't try to use it on FreeBSD unless you need it.

Building UxPlay on macOS: (Only tested on Intel X86_64 Macs)

Note: A native AirPlay Server feature is included in macOS 12 Monterey, but is restricted to recent hardware. UxPlay can run on older macOS systems that will not be able to run Monterey, or can run Monterey but not AirPlay.

These instructions for macOS asssume that the Xcode command-line developer tools are installed (if Xcode is installed, open the Terminal, type "sudo xcode-select --install" and accept the conditions).

It is also assumed that CMake = 3.13 is installed: this can be done with package managers MacPorts, Fink or Homebrew, or by a download from https://cmake.org/download/.

First get the latest macOS release of GStreamer-1.0 from https://gstreamer.freedesktop.org/download/. Install both the macOS runtime and development installer packages. Assuming that the latest release is 1.18.5 they are gstreamer-1.0-1.18.5-x86_64.pkg and gstreamer-1.0-devel-1.18.5-x86_64.pkg. Click on them to install (they install to /Library/FrameWorks/GStreamer.framework). It is recommended you use GStreamer.framework rather than install Gstreamer with Homebrew or MacPorts (see later).

Next install OpenSSL and libplist: these can be built from source (see below) but it is easier to get them using MacPorts "sudo port install openssl libplist-devel" or Homebrew "brew install openssl libplist". Only the static forms of the two libraries will used for the macOS build, so they do not need to remain installed after you have built uxplay: if you don't have MacPorts or Homebrew installed, you can just install one of these package-managers before building uxplay, and uninstall it afterwards if you do not want to keep it. Unfortunately, Fink's openssl11-dev package currently doesn't supply the static (libcrypto.a) form of the needed OpenSLL library libcrypto, and its libplist1 package is too old.

Finally, build and install uxplay (without ZOOMFIX): open a terminal and change into the UxPlay source directory ("UxPlay-master" for zipfile downloads, "UxPlay" for "git clone" downloads) and build/install with "cmake . ; make ; sudo make install " (same as for Linux).

On the macOS build, autovideosink uses OpenGL, not X11, to create the mirror display window (equivalent to "-vs glimagesink"; "-vs osxvideosink" can also be used). The window title does not show the Airplay server name, but it is visible to screen-sharing apps (e.g., Zoom). On macOS, The option -t timeout cannot be used because if the GStreamer pipeline is destroyed while the mirror window is still open, a segfault occurs (this is an issue with the GStreamer plugins, not UxPlay). Also, the resolution settings "-s wxh" do not affect the (small) initial OpenGL mirror window size, but the window can be expanded using the mouse or trackpad. In contrast, a window created with "-vs osxvideosink" is initially big, but has the wrong aspect ratio (stretched image); in this case the aspect ratio changes when the window width is changed by dragging its side.

Building OpenSSL and libplist from source on macOS

If you have have the standard GNU toolset (autoconf, automake, libtool, etc.) installed, you can also download and compile the source code for these libraries from https://www.openssl.org/source/, https://github.com/libimobiledevice/libplist. Install the downloaded openssl by opening a terminal in your Downloads directory, and unpacking the source distribution openssl-3.0.0.tar.gz , ("tar -xvzf openssl-3.0.0.tar.gz ; cd openssl-3.0.0"). Then build/install with "./config ; make ; sudo make install_dev" and clean up after building uxplay with "sudo make uninstall" in the same directory. Similarly, for libplist, download the source as a zipfile from github as libplist-master.zip, then unpack ("unzip libplist-master.zip ; cd libplist-master"), build/install ("./autogen.sh ; make ; sudo make install") and clean up after uxplay is built with "sudo make uninstall" in the same directory.

Other ways (Homebrew, MacPorts) to install GStreamer on macOS (not recommended):

First make sure that pkgconfig is installed (Homebrew: "brew install pkgconfig" ; MacPorts: "sudo port install pkgconfig" ).

(a) with Homebrew: "brew install gst-plugins-base gst-plugins-good gst-plugins-bad gst-libav". This appears to be functionally equivalent to using GStreamer.framework, but causes a large number of extra packages to be installed by Homebrew as dependencies. (However, as of November 2021, Homebrew offers a build of GStreamer for Apple Silicon, which then was not yet available on the offical GStreamer site.)

(b) with MacPorts: "sudo port install gstreamer1-gst-plugins-base gstreamer1-gst-plugins-good gstreamer1-gst-plugins-bad gstreamer1-gst-libav". The MacPorts GStreamer is built to use X11, so must be run from an XQuartz terminal, can use ZOOMFIX, and needs option "-vs ximagesink". On an older unibody MacBook Pro, the default resolution wxh = 1920x1080 was too large for the non-retina display, but using option "-s 800x600" worked; However, the GStreamer pipeline is fragile against attempts to change the X11 window size, or to rotations that switch a connected client between portrait and landscape mode while uxplay is running. Using the MacPorts X11 GStreamer is only viable if the image size is left unchanged from the initial "-s wxh" setting (also use the iPad/iPhone setting that locks the screen orientation against switching between portrait and landscape mode as the device is rotated).

Note: uxplay is run from a terminal command line, and informational messages are written to the terminal.

1. uxplay starts, but stalls after "Initialized server socket(s)" appears, without any server name showing on the client.

Stalling this way, with no server name showing on the client as available, probably means that your network does not have a running Bonjour/zeroconf DNS-SD server. On Linux, make sure Avahi is installed, and start the avahi-daemon service on the system running uxplay (your distribution will document how to do this). Some systems may instead use the mdnsd daemon as an alternative to provide DNS-SD service. (FreeBSD offers both alternatives, but only Avahi was tested: one of the steps needed for getting Avahi running on a FreeBSD system is to edit /usr/local/etc/avahi/avahi-daemon.conf to uncomment a line for airplay support.)

2. uxplay starts, but stalls after "Initialized server socket(s)" appears, with the server name showing on the client (but the client fails to connect when the UxPlay server is selected).

This shows that a dns_sd service is working, but a firewall on the server is probably blocking the connection request from the client. (One user who insisted that the firewall had been turned off turned out to have had two active firewalls (firewalld and ufw) both running on the server!) If possible, either turn off the firewall to see if that is the problem, or get three consecutive network ports, starting at port n, all three in the range 1024-65535, opened for both tcp and udp, and use "uxplay -p n" (or open UDP 6000, 6001, 6011 TCP 7000,7001,7100 and use "uxplay -p").

3. Problems after the client-server connection has been made:

For such problems, use "uxplay -d " (debug log option) to see what is happening: it will show how far the connection process gets before the failure occurs.

Most such problems are due to a GStreamer plugin that doesn't work on your system: (by default, GStreamer uses an algorithm to guess what is the "best" plugin to use on your system). A common case is that the GStreamer VAAPI plugin (for hardware-accelerated intel graphics) is being used on a system with nVidia graphics, If you use an nVidia graphics card, make sure that the gstreamer1.0-vaapi plugin for Intel graphics is NOT installed (uninstall it if it is installed!). (You can test for this by explicitly choosing the GStreamer videosink with option "-vs ximagesink" or "-vs xvimagesink", to see if this fixes the problem, or "-vs vaapisink" to see if this reproduces the problem.)

There are some reports of other GStreamer problems with hardware-accelerated Intel graphics. One user (on Debian) solved this with "sudo apt install intel-media-va-driver-non-free". This is a driver for 8'th (or later) generation "*-lake" Intel chips, that seems to be related to VAAPI accelerated graphics.

You can try to fix audio problems by using the "-as audiosink" option to choose the GStreamer audiosink , rather than have autoaudiosink pick one for you. The command "gst_inspect-1.0 | grep Sink | grep Audio" " will show you which audiosinks are available on your system. (Replace "Audio" by "Video" to see videosinks). Some possible audiosinks are pulsesink, alsasink, osssink, oss4sink, and osxaudiosink (macOS).

If you ran cmake with "-DZOOMFIX=ON", check if the problem is still there without ZOOMFIX. ZOOMFIX is only applied to the default videosink choice ("autovideosink") and the two X11 videosinks "ximagesink" and "xvimagesink". ZOOMFIX is only designed for these last two; if autovideosink chooses a different videosink, ZOOMFIX is now ignored. If you are using the X11 windowing system (standard on Linux), and have trouble with screen-sharing on Zoom, use ZOOMFIX and "-vs xvimagesink" (or "-vs ximagesink" if the previous choice doesn't work).

As other videosink choices are not affected by ZOOMFIX, they may or may not be visible to screen-sharing apps. Cairo-based windows created on Linux with "-vs gtksink" are visible to screen-sharing aps without ZOOMFIX; windows on macOS created by "-vs glimagesink" (default choice) and "-vs osximagesink" are also visible.

The "OpenGL renderer" window created on Linux by "-vs glimagesink" sometimes does not close properly when its "close" button is clicked. (this is a GStreamer issue). You may need to terminate uxplay with Ctrl-C to close a "zombie" OpenGl window.

4. GStreamer issues (missing plugins, etc.):

To troubleshoot GStreamer execute "export GST_DEBUG=2" to set the GStreamer debug-level environment-variable in the terminal where you will run uxplay, so that you see warning and error messages; (replace "2" by "4" to see much (much) more of what is happening inside GStreamer). Run "gst-inspect-1.0" to see which GStreamer plugins are installed on your system.

Some extra GStreamer packages for special plugins may need to be installed (or reinstalled: a user using a Wayland display system as an alternative to X11 reported that after reinstalling Lubuntu 18.4, UxPlay would not work until gstreamer1.0-x was installed, presumably for Wayland's X11-compatibility mode). Different distributions may break up GStreamer 1.x into packages in different ways; the packages listed above in the build instructions should bring in other required GStreamer packages as dependencies, but will not install all possible plugins.

5. Failure to decrypt ALL video and audio streams from a particular (older) client:

This triggers an error message, and will be due to use of an incorrect protocol for getting the AES decryption key from the client.

Modern Apple clients use a more-encrypted protocol than older ones. Which protocol is used by UxPlay depends on the client User-Agent string (reported by the client and now shown in the terminal output). iOS 9 and 10 clients only use iTunes FairPlay encryption on the AES decryption key they send to the server. Somewhere around iOS sourceVersion 330 (part of the User-Agent string) Apple started to further encrypt it by a sha-512 hash with a "shared secret" created during the Server-Client pairing process. The sourceVersion 330 above which the extra decryption step is carried out is set in lib/global.h if you need to change it. (This applies only to audio decryption; the AES key used for video decryption has had this extra encryption since iOS 9).

The third-party non-free Windows software AirMyPC (a commercial AirPlay emulator) uses an unhashed AES key for both audio and video encryption. AirMyPC has a distinctive User-Agent string, which is detected using two other settings in lib/global.h that can be adjusted if necessary. These settings might be useful if other AirPlay-emulators need support. Uxplay declares itself to be an AppleTV2,1 with sourceVersion 220.68; this can also be changed in global.h.

Options:

-n server_name (Default: UxPlay); server_name@hostname will be the name that appears offering AirPlay services to your iPad, iPhone etc, where hostname is the name of the server running uxplay. This will also now be the name shown above the mirror display (X11) window.

-nh Do not append "@hostname" at the end of the AirPlay server name.

-s wxh (e.g. -s 1920x1080 , which is the default ) sets the display resolution (width and height, in pixels). (This may be a request made to the AirPlay client, and perhaps will not be the final resolution you get.) w and h are whole numbers with four digits or less. Note that the height pixel size is the controlling one used by the client for determining the streaming format; the width is dynamically adjusted to the shape of the image (portrait or landscape format, depending on how an iPad is held, for example).

-s wxh@r As above, but also informs the AirPlay client about the screen refresh rate of the display. Default is r=60 (60 Hz); r is a whole number with three digits or less. Values greater than 255 are invalid.

-fps n sets a maximum frame rate (in frames per second) for the AirPlay client to stream video; n must be a whole number with 3 digits or less. (The client may choose to serve video at any frame rate lower than this; default is 30 fps.) A setting below 30 fps might be useful to reduce latency if you are running more than one instance of uxplay at the same time. Values greater than 255 are ignored. This setting is only an advisory to the client device, so setting a high value will not force a high framerate. (You can test using "-vs fpsdisplaysink" to see what framerate is being received.)

-o turns on an "overscanned" option for the display window. This reduces the image resolution by using some of the pixels requested by option -s wxh (or their default values 1920x1080) by adding an empty boundary frame of unused pixels (which would be lost in a full-screen display that overscans, and is not displayed by gstreamer). Recommendation: don't use this option unless there is some special reason to use it.

-p allows you to select the network ports used by UxPlay (these need to be opened if the server is behind a firewall). By itself, -p sets "legacy" ports TCP 7100, 7000, 7001, UDP 6000, 6001, 7011. -p n (e.g. -p 35000) sets TCP and UDP ports n, n+1, n+2. -p n1,n2,n3 (comma-separated values) sets each port separately; -p n1,n2 sets ports n1,n2,n2+1. -p tcp n or -p udp n sets just the TCP or UDP ports. Ports must be in the range [1024-65535].

If the -p option is not used, the ports are chosen dynamically (randomly), which will not work if a firewall is running.

-m generates a random MAC address to use instead of the true hardware MAC number of the computer's network card. (Different server_name, MAC addresses, and network ports are needed for each running uxplay if you attempt to run two instances of uxplay on the same computer.) If UxPlay fails to find the true MAC address of a network card, (more specifically, the MAC address used by the first active network interface detected) a random MAC address will be used even if option -m was not specifed. (Note that a random MAC address will be different each time UxPlay is started).

Also: image transforms that had been added to RPiPlay have been ported to UxPlay:

-f {H|V|I} implements "videoflip" image transforms: H = horizontal flip (right-left flip, or mirror image); V = vertical flip ; I = 180 degree rotation or inversion (which is the combination of H with V).

-r {R|L} 90 degree Right (clockwise) or Left (counter-clockwise) rotations; these are carried out after any -f transforms.

-vs videosink chooses the GStreamer videosink, instead of letting autovideosink pick it for you. Some videosink choices are: ximagesink, xvimagesink, vaapisink (for intel graphics), gtksink, glimagesink, waylandsink, osximagesink (for macOS), or fpsdisplaysink (which shows the streaming framerate in fps). Using quotes "..." might allow some parameters to be included with the videosink name. (Some choices of videosink might not work on your system.)

-vs 0 suppresses display of streamed video, but plays streamed audio. (The client's screen is still mirrored at a reduced rate of 1 frame per second, but is not rendered or displayed.) This feature (which streams audio in AAC audio format) is now probably unneeded, as UxPlay can now stream superior-quality Apple Lossless audio without video in Airplay non-mirror mode.

-as audiosink chooses the GStreamer audiosink, instead of letting autoaudiosink pick it for you. Some audiosink choices are: pulsesink, alsasink, osssink, oss4sink, and osxaudiosink (for macOS). Using quotes "..." might allow some parameters to be included with the audiosink name. (Some choices of audiosink might not work on your system.)

-as 0 (or just -a) suppresses playing of streamed audio, but displays streamed video.

-t timeout will cause the server to relaunch (without stopping uxplay) if no connections have been present during the previous timeout seconds. You may wish to use this if the Server is not visible to new Clients that were inactive when the Server was launched, and an idle Bonjour registration eventually becomes unavailable for new connections (this is a workaround for what may be due to a problem with your dns-sd or Avahi setup). This option should not be used on macOS, as a window created by GStreamer does not terminate correctly (it causes a segfault) if it is still open when the GStreamer pipeline is closed.

1.44 2021-12-13 Omit hash of aeskey with ecdh_secret if sourceVersion = 280.33 (this supports AirMyPC); internal rearrangement of where this hash is done. Replace decodebin by h264-specific elements in the GStreamer video pipeline. Fully report initial communications between client and server in -d debug mode.

1.43 2021-12-07 Various internal changes, such as tests for successful decryption, uniform treatment of informational/debug messages, etc., updated README.

1.42 2021-11-20 Fix MAC detection to work with modern Linux interface naming practices, MacOS and *BSD.

1.41 2021-11-11 Further cleanups of multiple audio format support (internal changes, separated RAOP and GStreamer audio/video startup)

1.40 2021-11-09 Cleanup segfault in ALAC support, manpage location fix, show request Plists in debug mode.

1.39 2021-11-06 Added support for Apple Lossless (ALAC) audio streams.

1.38 2021-10-8 Add -as audiosink option to allow user to choose the GStreamer audiosink.

1.37 2021-09-29 Append "@hostname" to AirPlay Server name, where "hostname" is the name of the server running uxplay (reworked change in 1.36).

1.36 2021-09-29 Implemented suggestion (by @mrbesen and @PetrusZ) to use hostname of machine runing uxplay as the default server name

1.35.1 2021-09-28 Added the -vs 0 option for streaming audio, but not displaying video.

1.35 2021-09-10 now uses a GLib MainLoop, and builds on macOS (tested on Intel Mac, 10.15 ). New option -t timeout for relaunching server if no connections were active in previous timeout seconds (to renew Bonjour registration).

1.341 2021-09-04 fixed: render logger was not being destroyed by stop_server()

1.34 2021-08-27 Fixed "ZOOMFIX": the X11 window name fix was only being made the first time the GStreamer window was created by uxplay, and not if the server was relaunched after the GStreamer window was closed, with uxplay still running. Corrected in v. 1.34

  1. Updates of the RAOP (AirPlay protocol) collection of codes maintained at https://github.com/FD-/RPiPlay.git so it is current as of 2021-08-01, adding all changes since the original release of UxPlay by antimof. This involved crypto updates, replacement of the included plist library by the system-installed version, and a change over to a library llhttp for http parsing.

  2. Added the -s, -o -p, -m, -r, -f, -fps -vs -as and -t options.

  3. If "cmake -DZOOMFIX=ON ." is run before compiling, the mirrored window is now visible to screen-sharing applications such as Zoom. To compile with ZOOMFIX=ON, the X11 development libraries must be installed. (ZOOMFIX will not be needed once the upcoming gstreamer-1.20 is available, since starting with that release, the GStreamer X11 mirror window will be natively visible for screen-sharing.) Thanks to David Ventura https://github.com/DavidVentura/UxPlay for the fix and also for getting it into gstreamer-1.20. [If uxplay was compiled after cmake was run without -DZOOMFIX=ON, and your gstreamer version is older than 1.20, you can still manually make the X11 window visible to screen-sharing apps with the X11 utility xdotool, if it is installed, with: xdotool selectwindow set_window --name name (where name is your choice of name), and then select the uxplay window by clicking on it with the mouse.]

  4. The AirPlay server now terminates correctly when the gstreamer display window is closed, and is relaunched with the same settings to wait for a new connection. The program uxplay terminates when Ctrl-C is typed in the terminal window. The -t timeout option relaunches the server after timeout seconds of inactivity to allow new connections to be made.

  5. In principle, multiple instances of uxplay can be run simultaneously using the -m (generate random MAC address) option to give each a different ("local" as opposed to "universal") MAC address. If the -p [n] option is used, they also need separate network port choices. (However, there may be a large latency, and running two instances of uxplay simultaneously on the same computer may not be very useful; using the -fps option to force streaming framerates below 30fps could be helpful.)

  6. Without the -p [n] option, uxplay makes a random dynamic assignment of network ports. This will not work if most ports are closed by a firewall. With e.g., -p 45000 you should open both TCP and UDP on ports 45000, 45001, 45002. Minimum allowed port is 1024, maximum is 65535. The option "-p" with no argument uses a "legacy" set of ports TCP 7100, 7000, 7001, and UDP 7011, 6000, 6001. Finer control is also possible: "-p udp n1,n2,n3 -p tcp n4,n5,n6" sets all six ports individually.

  7. The default resolution setting is 1920x1080 width x height pixels. To change this, use "-s wxh" where w and h are positive decimals with 4 or less digits. It seems that the width and height may be negotiated with the AirPlay client, so this may not be the actual screen geometry that displays.

  8. The title on the GStreamer display window is now is the AirPlay server name. (This works for X11 windows created by gstreamer videosinks ximagesink, xvimagesink, but not OpenGL windows created by glimagesink.)

  9. The avahi_compat "nag" warning on startup is suppressed, by placing "AVAHI_COMPAT_NOWARN=1" into the runtime environment when uxplay starts. (This uses a call to putenv() in a form that is believed to be safe against memory leaks, at least in modern Linux; if for any reason you don't want this fix, comment out the line in CMakeLists.txt that activates it when uxplay is compiled.) On macOS, Avahi is not used.

  10. UxPlay now builds on macOS.

  11. The hostname of the server running uxplay is now appended to the AirPlay server name, which is now displayed as name@hostname, where name is "UxPlay", (or whatever is set with the -n option).

  12. Added support for audio-only streaming with original (non-Mirror) AirPlay protocol, with Apple Lossless (ALAC) audio.

  13. Added suppport for the older AirPlay protocol used by third-party Windows-based AirPlay mirror emulators such as AirMyPC.

All the resources in this repository are written using only freely available information from the internet. The code and related resources are meant for educational purposes only. It is the responsibility of the user to make sure all local laws are adhered to.

This project makes use of a third-party GPL library for handling FairPlay. The legal status of that library is unclear. Should you be a representative of Apple and have any objections against the legality of the library and its use in this project, please contact me and I'll take the appropriate steps.

Given the large number of third-party AirPlay receivers (mostly closed-source) available for purchase, it is my understanding that an open source implementation of the same functionality wouldn't violate any of Apple's rights either.

(From the https://github.com/FD-/RPiPlay.git repository.)

RPiPlay authors

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

  • dsafa22: Created an AirPlay 2 mirroring server (seems gone now, but code is preserved here, and see here for dsafa22's description of the analysis of the AirPlay 2 mirror protocol that made RPiPlay possible) 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/ concerning mirroring is dsafa22's work. License: GNU LGPLv2.1+
  • 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
  • Joyent, Inc and contributors: Created an http library called llhttp. Located at lib/llhttp/. License: MIT
  • Team XBMC: Managed to show a black background for OpenMAX video rendering. This code is used in the video renderer. License: GNU GPL
  • Alex Izvorski and contributors: Wrote h264bitstream, a library for manipulation h264 streams. Used for reducing delay in the Raspberry Pi video pipeline. Located in the renderers/h264-bitstream folder. License: GNU LGPLv2.1

AirPlay protocol versions

For multiple reasons, it's very difficult to clearly define the protocol names and versions of the components that make up the AirPlay streaming system. In fact, it seems like the AirPlay version number used for marketing differs from that used in the actual implementation. In order to tidy up this whole mess a bit, I did a little research that I'd like to summarize here:

The very origin of the AirPlay protocol suite was launched as AirTunes sometime around 2004. It allowed to stream audio from iTunes to an AirPort Express station. Internally, the name of the protocol that was used was RAOP, or Remote Audio Output Protocol. It seems already back then, the protocol involved AES encryption. A public key was needed for encrypting the audio sent to an AirPort Express, and the private key was needed for receiving the protocol (ie used in the AirPort Express to decrypt the stream). Already in 2004, the public key was reverse-engineered, so that third-party sender applications were developed.

Some time around 2008, the protocol was revised and named AirTunes 2. It seems the changes primarily concerned timing. By 2009, the new protocol was reverse-engineered and documented.

When the Apple TV 2nd generation was introduced in 2010, it received support for the AirTunes protocol. However, because this device allowed playback of visual content, the protocol was extended and renamed AirPlay. It was now possible to stream photo slideshows and videos. Shortly after the release of the Apple TV 2nd generation, AirPlay support for iOS was included in the iOS 4.2 update. It seems like at that point, the audio stream was still actually using the same AirTunes 2 protocol as described above. The video and photo streams were added as a whole new protocol based on HTTP, pretty much independent from the audio stream. Soon, the first curious developers began to investigate how it worked. Their conclusion was that visual content is streamed unencrypted.

In April 2011, a talented hacker extracted the AirPlay private key from an AirPort Express. This meant that finally, third-party developers were able to also build AirPlay receiver (server) programs.

For iOS 5, released in 2011, Apple added a new protocol to the AirPlay suite: AirPlay mirroring. Initial investigators found this new protocol used encryption in order to protect the transferred video data.

By 2012, most of AirPlay's protocols had been reverse-engineered and documented (see also updated version). At this point, audio still used the AirTunes 2 protocol from around 2008, video, photos and mirroring still used their respective protocols in an unmodified form, so you could still speak of AirPlay 1 (building upon AirTunes 2). The Airplay server running on the Apple TV reported as version 130. The setup of AirPlay mirroring used the xml format, in particular a stream.xml file. Additionally, it seems like the actual audio data is using the ALAC codec for audio-only (AirTunes 2) streaming and AAC for mirror audio. At least these different formats were used in later iOS versions.

Sometime before iOS 9, the protocol for mirroring was slightly modified: Instead of the "stream.xml" API endpoint, the same information could also be querried in binary plist form, just by changing the API endpoint to "stream", without any extension. I wasn't able to figure out which of these was actually used by what specific client / server versions.

For iOS 9, Apple made considerable changes to the AirPlay protocol in 2015, including audio and mirroring. Apparently, the audio protocol was only slightly modified, and a minor change restored compatibility. For mirroring, an additional pairing phase was added to the connection establishment procedure, consisting of pair-setup and pair-verify calls. Seemingly, these were added in order to simplify usage with devices that are connected frequently. Pair-setup is used only the first time an iOS device connects to an AirPlay receiver. The generated cryptographic binding can be used for pair-verify in later sessions. Additionally, the stream / stream.xml endpoint was replaced with the info endpoint (only available as binary plist AFAICT). As of iOS 12, the protocol introduced with iOS 9 was still supported with only slight modifications, albeit as a legacy mode. While iOS 9 used two SETUP calls (one for general connection and mirroring video, and one for audio), iOS 12 legacy mode uses 3 SETUP calls (one for general connection (timing and events), one for mirroring video, one for audio).

The release of tvOS 10.2 broke many third-party AirPlay sender (client) programs in 2017. The reason was that it was now mandatory to perform device verification via a pin in order to stream content to an Apple TV. The functionality had been in the protocol before, but was not mandatory. Some discussion about the new scheme can be found here. A full specification of the pairing and authentication protocol was made available on GitHub. At that point, tvOS 10.2 reported as AirTunes/320.20.

In tvOS 11, the reported server version was increased to 350.92.4.

iOS 11.4 added AirPlay 2 in 2018. Although extensively covered by the media, it's not entirely clear what changes specifically Apple has made protocol-wise.

From captures of the traffic between an iOS device running iOS 12.2 and an AppleTV running tvOS 12.2.1, one can see that the communication on the main mirroring HTTP connection is encrypted after the initial handshake. This could theoretically be part of the new AirPlay 2 protocol. The AppleTV running tvOS 12.2.1 identifies as AirTunes/380.20.1. When connecting from the same iOS device to an AppleTV 3rd generation (reporting as AirTunes/220.68), the communication is still visible in plain. From the log messages that the iOS device produces when connected to an AppleTV 3rd generation, it becomes apparent that the iOS device is treating this plain protocol as the legacy protocol (as originally introduced with iOS 9). Further research showed that at the moment, all available third-party AirPlay mirroring receivers (servers) are using this legacy protocol, including the open source implementation of dsafa22, which is the base for RPiPlay. Given Apple considers this a legacy protocol, it can be expected to be removed entirely in the future. This means that all third-party AirPlay receivers will have to be updated to the new (fully encrypted) protocol at some point.

More specifically, the encryption starts after the pair-verify handshake completed, so the fp-setup handshake is already happening encrypted. Judging from the encryption scheme for AirPlay video (aka HLS Relay), likely two AES GCM 128 ciphers are used on the socket communication (one for sending, one for receiving). However, I have no idea how the keys are derived from the handshake data.

Related Posts