Add Readme

Author: knuesel

README.md

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+A GStreamer plugin that provides an `airplaysrc` element for receiving video
+streamed from Apple devices using the AirPlay protocol. Audio is currently not
+supported.
+
+## Installation
+
+See [below](#building) for build instructions. Once you have the file `libgstairplay.so`,
+you must let GStreamer find it. Possibilities include:
+
+* Placing the `libgstairplay.so` file in `~/.local/share/gstreamer-1.0/plugins`.
+* Using the `--gst-plugin-path` option with `gst-launch` (for example `gst-launch-1.0 --gst-plugin-path=~/my-gst-plugins` airplaysrc ! ...`, see below for complete pipelines).
+* Add the directory containing the plugin to the `GST_PLUGIN_PATH` environment variable.
+
+## Usage
+
+The `airplaysrc` element can be used like other video sources in GStreamer
+pipelines. Examples are shown below.
+
+Typical use will require the following packages (tested on Ubuntu 20.04):
+
+```
+gstreamer1.0-tools
+gstreamer1.0-plugins-good
+gstreamer1.0-plugins-bad
+gstreamer1.0-libav
+libavahi-compat-libdnssd1
+libplist3
+```
+
+### Showing the video in a window
+
+The `gst-launch` tool can be used to run a pipeline that shows the video stream
+in a new window:
+
+```
+gst-launch-1.0 airplaysrc ! queue ! h264parse ! avdec_h264 max-threads=1 ! autovideosink
+```
+
+Explanation: the video stream is received in the H.264 format. The stream must
+be parsed (`h264parse`) and decoded (`avdec_h264`) before showing in a window
+(`autovideosink`). The `queue` element adds some buffering. The `max-threads=1`
+decoding option can help reduce latency.
+
+### Using as a source in OBS Studio
+
+The `airplaysrc` element can be used with the [OBS GStreamer
+plugin](https://github.com/fzwoch/obs-gstreamer) to configure an OBS source
+that shows the AirPlay video stream:
+
+1. Install the OBS Gstreamer plugin. After compiling, I put the file `obs-gstreamer.so` in the directory `~/.config/obs-studio/plugins/obs-gstreamer/bin/64bit/`.
+1. In your OBS scene, add a "GStreamer Source"
+1. Set the pipeline parameter, using `airplaysrc` as first element. I use the following:
+
+       airplaysrc ! queue ! h264parse ! avdec_h264 max-threads=1 ! videoconvert ! videoscale ! video.
+
+1. For best results, set the canvas and output sizes to the resolution of the AirPlay stream.
+
+### Using as a Linux camera device
+
+Using the [v4l2loopback](https://github.com/umlaeute/v4l2loopback) kernel
+module, you can expose the AirPlay video stream as a camera device in Linux.
+
+1. Install the `v4l2loopback` module. Your distribution might have it as a package, for example `v4l2loopback-dkms` in Ubuntu 20.04.
+1. Load the module with appropriate options. I use the following:
+
+       sudo modprobe v4l2loopback devices=1 video_nr=10 card_label="AirPlay Cam" exclusive_caps=1 max_buffers=3
+
+   This creates a virtual camera with name "AirPlay Cam" and device `/dev/video10`.
+
+1. Start a GStreamer pipeline that feeds the AirPlay stream to the video device:
+
+       gst-launch-1.0 -v airplaysrc ! queue ! h264parse ! avdec_h264 max-threads=1 ! videoconvert ! videoscale ! v4l2sink device=/dev/video10
+
+Once you start streaming from the Apple device, you should see "AirPlay Cam" in the list of cameras on your computer.
+
+## Troubleshooting
+
+Call `gst-inspect-1.0 libgstairplay.so` (giving the path where the
+`libgstairplay.so` file is located) to check for problems such as missing
+libraries. For example if it says `libplist.so.3: cannot open shared object
+file: No such file or directory`, you can fix it by installing the `libplist3`
+package (on Ubuntu 20.04 at least).
+
+If you get an uninformative error message such as `Could not load plugin file:
+File "libgstairplay.so" appears to be a GStreamer plugin, but it failed to
+initialize`, try running again with `GST_DEBUG=4 gst-inspect-1.0
+build/libgstairplay.so`.
+
+## Building
+
+First install the build dependencies. The following packages are needed on
+Ubuntu 20.04:
+
+```
+git
+gcc
+pkg-config
+cmake
+gstreamer1.0-tools
+libgstreamer1.0-dev
+libgstreamer-plugins-base1.0-dev
+libavahi-compat-libdnssd-dev
+libplist-dev
+libssl-dev
+meson
+ninja-build
+```
+
+Then clone and build RPiPlay. The fork at https://github.com/knuesel/RPiPlay is
+currently required. I use the following commands:
+
+```
+git clone https://github.com/knuesel/RPiPlay
+cd RPiPlay
+mkdir -p build install
+cd build
+cmake -DCMAKE_INSTALL_PREFIX=../install ..
+make install
+```
+
+Then clone and build this project. I use the following:
+
+```
+cd ../..  # Get out of the RPiPlay directory
+export PKG_CONFIG_PATH=$PKG_CONFIG_PATH:$PWD/RPiPlay/install/lib/pkgconfig
+git clone https://github.com/knuesel/gst-airplay
+cd gst-airplay
+meson build
+ninja -C build
+```
+
+You should now have the compiled plugin `libgstairplay.so` in the `build`
+directory. To check that it is a valid GStreamer plugin, run:
+
+```
+gst-inspect-1.0 build/libgstairplay.so 
+```
+
+This should display something such as
+
+```
+Plugin Details:
+  Name                     airplay
+  Description              receive video through Apple AirPlay
+  Filename                 build/libgstairplay.so
+  Version                  0.1
+  License                  GPL
+  Source module            gst-airplay-plugin
+  Binary package           GStreamer airplay Plug-ins
+  Origin URL               https://github.com/knuesel/gst-airplay
+
+  airplaysrc: AirPlay source
+
+  1 features:
+  +-- 1 elements
+```
+
+If you get an error message, see the [troubleshooting](#troubleshooting) section.
+
+## Credits
+
+The pluging code is based on
+[gst-template](https://gitlab.freedesktop.org/gstreamer/gst-template/) and uses
+the AirPlay implementation from [RPiPlay](https://github.com/FD-/RPiPlay).
+
+## License
+
+The plugin makes use of [RPiPlay](https://github.com/FD-/RPiPlay) so it is
+licensed under the GNU GPL 3.0.