2.7 KiB
External Libraries in Open Screen
Currently, external libraries are used exclusively by the standalone sender and receiver applications, for compiling in dependencies used for video decoding and playback.
The decision to link external libraries is made manually by setting the GN args.
For example, a developer wanting to link all the libraries for the standalone
sender and receiver executables might add the following to gn args out/Default:
is_debug=true
have_ffmpeg=true
have_libsdl2=true
have_libopus=true
have_libvpx=true
On some versions of Debian, the following apt-get command will install all of the necessary external libraries for Open Screen:
sudo apt-get install libsdl2-2.0 libsdl2-dev libavcodec libavcodec-dev
libavformat libavformat-dev libavutil libavutil-dev
libswresample libswresample-dev libopus0 libopus-dev
libvpx5 libvpx-dev
Similarly, on some versions of Raspian, the following command will install the necessary external libraries, at least for the standalone receiver. Note that this command is based off of the packages linked in the sysroot:
sudo apt-get install libavcodec58=7:4.1.4* libavcodec-dev=7:4.1.4*
libsdl2-2.0-0=2.0.9* libsdl2-dev=2.0.9*
libavformat-dev=7:4.1.4*
Note: release of these operating systems may require slightly different
packages, so these sh commands are merely a potential starting point.
Finally, note that generally the headers for packages must also be installed.
In Debian Linux flavors, this usually means that the *-dev version of each
package must also be installed. In the example above, this looks like having
both libavcodec and libavcodec-dev.
Standalone Sender
The standalone sender uses FFMPEG, LibOpus, and LibVpx for encoding video and audio for sending. When the build has determined that have_external_libs is set to true, meaning that all of these libraries are installed, then the VP8 and Opus encoders are enabled and actual video files can be sent to standalone receiver instances. Without these dependencies, the standalone sender cannot properly function (contrasted with the standalone receiver, which can use a dummy player).
Standalone Receiver
The standalone receiver also uses FFMPEG, for decoding the video stream encoded by the sender, and also uses LibSDL2 to create a surface for decoding video. Unlike the sender, the standalone receiver can work without having its have_external_libs set to true, through the use of its Dummy Player.