UxPlay/README.txt

UxPlay 1.40
===========

This project is a GPLv3 unix AirPlay server which now also works on
macOS. Its main use is to act like an AppleTV for screen-mirroring (with
audio) of iOS/macOS clients (iPads, iPhones, 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, using Apple's AirPlay Mirror protocol first
available in iOS 5. (Details of what is known about the AirPlay2
protocol can be found
[here](https://github.com/SteeBono/airplayreceiver/wiki/AirPlay2-Protocol)
and [here](https://emanuelecozzi.net/docs/airplay2)).

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 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](https://www.avahi.org), through the avahi-daemon service, and is
included in most Linux distributions (this service can also be provided
by macOS, iOS or Windows servers).

*New: UxPlay 1.40 now also supports the Airplay audio-only protocol as
well as AirPlay Mirror protocol, and (when the client screen is not
being mirrored) can play Apple Lossless (ALAC) 44100/16/2 audio streamed
from the client in 2-channel stereo without video (the accompanying
cover-art and metadata is received by the server, but not displayed).*

UxPlay 1.40 is based on https://github.com/FD-/RPiPlay, with GStreamer
integration from https://github.com/antimof/UxPlay. (UxPlay only uses
GStreamer, and does not contain the alternative Raspberry-Pi-specific
audio and video renderers also found in RPiPlay.) Tested on Ubuntu
20.04, Linux Mint 20.2, OpenSUSE 15.3, macOS 10.15.

Features: 1. Based on Gstreamer. 2. Video and audio are supported out of
the box. 3. Gstreamer decoding is plugin agnostic. Uses accelerated
decoders if available. VAAPI is preferable, (but don't use VAAPI with
nVidia). 4. Automatic screen orientation.

Getting UxPlay:
===============

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

*This is a pull request on the original site
https://github.com/antimof/UxPlay ; it may or may not ever get committed
into the codebase on the antimof site, as that project appears to no
longer be active. If the pull request ever gets committed, replace
"FDH2" by "antimof" in the above.*

Building this version:
======================

(Instructions for 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. (For recent glibc (or libc6) 2.32 or later, an
obsolete RPC header file netdb.h (needed by UxPlay) has been removed;
install libtirpc-dev which now provides a compatible implementation, if
the compiler reports that it is missing.)

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 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)

*Note that older cmake does not require the final "`.`" to specify the
current directory as the source directory, but newer cmake requires it.
If you intend to modify the code, use a separate "build" directory:
replace "cmake \[ \] ." by "mkdir build ; cd build ; cmake \[ \] ..";
you can then get back to the clean source (with any changes you made)
with "cd .. ; rm -rf build".*

The above script installs the executable file "`uxplay`" to
`/usr/local/bin`, (and installs a manpage to `/usr/local/man/man1` and
README files to `/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 (which must be for libplist version 2.0 or greater)
and (for ZOOMFIX) libx11-dev are new dependencies. Older 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, and you don't wish to upgrade, see the instructions below
(in the macOS section) on building libplist from source (you need
autoconf, automake, libtool, and may need to also install some
libpython\*-dev package) but (unlike the statically-linked macOS case)
do not uninstall the libplist library after building uxplay; it must
remain installed. It is in /usr/local/lib. If uxplay fails to find
libplist when you run it, this is probably because /usr/local/lib is not
in the library path (by default, this is the case in ubuntu). To fix
this, run "sudo ldconfig" (you might also need to create a file
/etc/ld.so.conf.d/libplist.conf containing the text "/usr/local/lib"
before running 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).

**macOS** (Intel X86\_64 Macs only):

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

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](http://www.macports.org),
[Fink](http://finkproject.org) or [Homebrew](http://brew.sh), 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-1.1.1 and libplist: these can be built from source
(see below) but it's 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 don't want to keep it. Unfortunately,
Fink's openssl11-dev package currently doesn't supply the static
(libcrypto.a) form of the needed 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).

The macOS build uses OpenGL, not X11, to create the mirror display
window. This has some "quirks": the window title is "OpenGL renderer"
instead of the Airplay server name, but it is visible to screen-sharing
apps (e.g., Zoom). The option -t *timeout* cannot be used because if the
GStreamer pipeline is destroyed while the OpenGL window is still open,
and uxplay is left running, a segfault occurs (this is an issue with the
glimagesink GStreamer OpenGL plugin, not UxPlay). Also, the resolution
settings "-s wxh" do not affect the (small) initial mirror window size,
but the window can be expanded using the mouse or trackpad.

***Building OpenSSL-1.1.1 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-1.1.1 by opening a terminal in your Downloads directory, and
unpacking the source distribution openssl-1.1.1x.tar.gz (where "x" is a
"patch" label, currently given by "x" = "l"): ("tar -xvzf
openssl-1.1.1x.tar.gz ; cd openssl-1.1.1x"). 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](https://github.com/libimobiledevice/libplist/archive/refs/heads/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-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.

(b) with MacPorts: "sudo port install 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).

**Troubleshooting:**
====================

If uxplay starts, but stalls after "Initialized server socket(s)"
appears, it is probably because a firewall is blocking access to the
server on which it is running. 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").

Stalling after "Initialize server socket(s)", with the server showing as
available on the client iPad/iPhone, is almost certainly a firewall
problem: one user was unaware that *two* firewalls (ufw and firewalld)
were both active on their system.

Stalling this way, but *without* the server showing as available on the
client, 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 (your distribution will
document how to do this). Some systems may instead use the mdnsd daemon
as an alternative to provide DNS-SD service.

For other problems after a connection is made, use "uxplay -d" (debug
log option) to see what is happening. **Such problems are usually 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). 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.)

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.

**Usage:**
==========

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.

**-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.) On macOS, random MAC addresses are always used.

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.)

**-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 **-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 because the Server may not
be visible to new Clients that were inactive when the Server was
launched, and an idle Bonjour registration also eventually becomes
unavailable for new connections.) The timer only starts once a Client
has first made a mirror connection and then has disconnected with "Stop
Mirrroring". *This option should **not** be used if the display window
is an OpenGL window on macOS, as such an OpenGL window created by
GStreamer does not terminate correctly (it causes a segfault) if it is
still open when the GStreamer pipeline is closed.*

ChangeLog
=========

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

Improvements since the original UxPlay by antimof:
==================================================

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).

Disclaimer
==========

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.

RPiPlay Authors (Notes by fdraschbacher, RPiPlay creator.)
==========================================================

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

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](https://github.com/dsafa22/AirplayServer)(seems gone now)
    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](https://github.com/juhovh/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](https://github.com/EstebanKubata/playfair). Located in
    the `lib/playfair` folder. License: GNU GPL
-   **Joyent, Inc and contributors**: Created an http library called
    [llhttp](https://github.com/nodejs/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](https://github.com/aizvorski/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

RPiPlay Changelog
=================

### Version 1.2

-   Blank screen after connection stopped

### Version 1.1

-   Now audio and video work on Raspberry Pi Zero. I don't know what
    exactly did the trick, but static compilation seems to have helped.
-   Smoother video due to clock syncing
-   Correct lip-sync due to clock syncing
-   Lower latency due to injecting max\_dec\_frame\_buffering into SPS
    NAL
-   Disabled debug logging by default
-   Added command line flag for debug logging
-   Added command line flag for unsynchronized low-latency mode
-   Bug fixes

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](http://nanocr.eu/2004/08/11/reversing-airtunes/) were
developed.

Some time [around
2008](https://weblog.rogueamoeba.com/2008/01/10/a-tour-of-airfoil-3/),
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](https://git.zx2c4.com/Airtunes2/about/).

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](https://web.archive.org/web/20101211213705/http://www.tuaw.com/2010/12/08/dear-aunt-tuaw-can-i-airplay-to-my-mac/).
Their conclusion was that visual content is streamed unencrypted.

In April 2011, a talented hacker [extracted the AirPlay private
key](http://www.macrumors.com/2011/04/11/apple-airplay-private-key-exposed-opening-door-to-airport-express-emulators/)
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](https://www.aorensoftware.com/blog/2011/08/20/exploring-airplay-mirroring-internals/)
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](https://nto.github.io/AirPlay.html). 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](https://github.com/espes/Slave-in-the-Magic-Mirror/issues/12#issuecomment-372380451).

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](https://9to5mac.com/2015/09/11/apple-ios-9-airplay-improvements-screen-mirroring/)
to the AirPlay protocol in 2015, including audio and mirroring.
Apparently, the audio protocol was only slightly modified, and a [minor
change](https://github.com/juhovh/shairplay/issues/43) restored
compatibility. For mirroring, an [additional pairing
phase](https://github.com/juhovh/shairplay/issues/43#issuecomment-142115959)
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](https://github.com/postlund/pyatv/issues/79). A full
specification of the pairing and authentication protocol was made
available on
[GitHub](https://htmlpreview.github.io/?https://github.com/philippe44/RAOP-Player/blob/master/doc/auth_protocol.html).
At that point, tvOS 10.2 reported as AirTunes/320.20.

In tvOS 11, the reported server version was [increased to
350.92.4](https://github.com/ejurgensen/forked-daapd/issues/377#issuecomment-309213273).

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.