Screen Recorder QT

Project for the PDS course at the "Politecnico di Torino"

Group

• Francesco Cheinasso
• Alessandra Comparetto
• Alessandro Cannarella

About Project

Screen Recorder QT is a software based on two components.

• The first is the ScreenRecorder library, a multiplatform C++ library which allow to record the screen and optionally mux the audio recorded by the microphone with the captured video.
• The second is the QT application, a C++ native frontend based on QT libraries, used to interact with the ScreenRecorder library.

Screen Recorder Library

This is the core of the project. The library is composed by 2 main files ScreenRecorder.cpp and ScreenRecorder.h. It uses ffmpeg libraries to capture the frames (video and audio) , to elaborate them, and to save in a .mp4 file. Those libraries are avcodec, avdevice, avfilter, avformat and avutil.

It uses 2 threads for the video recording and an for the audio:

• Video:
  • Raw Packets Thread: It get the raw video frames from the os virtual device (x11grab on Linux, gdigrab on Windows and avFoundation on macOS) and insert them in a queue.
  • Elaboration Thread: This take the raw packets from the queue and decode and encode it in the new format and write them in the output file. It also perform scaling.
• Audio:
  • Microphone capture thread: It get the raw audio frames from an os virtual device (alsa on Linux, dshow on Windows and avFoundation on macOS) save them in a queue creating bursts that are then elaborated (decode and encode) and written in the output file.

Those are the features offered by the library:

• Record Screen Video without microphone audio
• Record Screen Video with microphone audio
• Pause and Resume recording without creating separated files.
• Compress the video by a value chosen by the user ( 0 disable compression )
• Rescale the video by a value chosen by the user, between 0.1 and 1 ( 1 means no rescaling, 0.5 half rescaling ).
• Allows the user to specify the position and the size of the portion of screen that have to be recorded, by a value chosen by the user.
• Allows the user to specify the screen number.
• Allows the user to specify the screen recording's fps, by a value chosen by the user.
• Allows the user to specify an audio input device (the library doesn't find the available devices, it is up to the application ).
• Allows the user to specify the output file name (it must end with .mp4 )
• In case of internal errors throws an exception with a description of the error and gracefully stop the registration (if the library is recording), creating the output file with what has been recorded till that moment.

QT Application

Allow to use the ScreenRecorder library, offering a GUI to set the parameters and to give commands.

In order to improve the user experience, the GUI create also an icon in the os system tray to interact with the library without using the main window.

It uses QTmultimedia library to find the available audio devices on Windows and MacOS. Instead on Linux is used the getAudioDevices function ( in getAudioDevices.cpp ), which return only the input audio devices.

The dimensions of the screen are retrieved with QGuiApplication and a portion of the screen can be selected using the AreaSelector ( AreaSelector.cpp ).

Screenshots

Legacy Applications

ScreenRecorder library can be used without the support of the GUI mentioned before. In the "legacy" versions, the user is able to record a video using the terminal window provided by the OS.

In this case, it's possible to control the action of the application by pressing the commands

• [1] to pause
• [2] to resume
• [3] to stop

Linux

How to run (QT application only)

• Download the latest binary from this link
• Install the required libraries with sudo apt install ffmpeg qt5-default (Needs QT 5.15 or higher versions)
• Allow the binary execution with chmod 777 ScreenRecorder_linux_amd64
• Run the program with ./ScreenRecorder_linux_amd64

How to compile, run and install

QT application

• Download the required Qt libraries sudo apt install qt5-qmake qtmultimedia5-dev
• Download the other required libraries and tools sudo apt install build-essential libasound2-dev libavcodec-dev libavdevice-dev libavfilter-dev libavformat-dev libavutil-dev
• Install c++ 20 sudo apt install gcc-10 gcc-10-base gcc-10-doc g++-10 sudo apt install libstdc++-10-dev libstdc++-10-doc
• Clone the repository git clone https://github.com/cheina97/ScreenRecorderQT.git
• Go in the project folder cd ScreenRecorderQT/ScreenRecorderQT/ScreenRecorderQT
• Generate the Makefile qmake ScreenRecorderQT.pro
• Compile it make clean; make all
• Allow the binary to be executed chmod 777 ScreenRecorderQT
• Run it ./ScreenRecorderQT
• (Optional) Install the binary and the desktop launcher in your system sudo make install. You can revert this operation with sudo make uninstall. The binary will be installed in /opt/ScreenRecorderQT/ScreenRecorderQT and the desktop launcher in /usr/share/applications/ScreenRecorderQT.

Legacy application

• Download the required libraries and tools sudo apt install build-essential libasound2-dev libavcodec-dev libavdevice-dev libavfilter-dev libavformat-dev libavutil-dev
• Install c++ 20 sudo apt install gcc-10 gcc-10-base gcc-10-doc g++-10 sudo apt install libstdc++-10-dev libstdc++-10-doc
• Clone the repository git clone https://github.com/cheina97/ScreenRecorderQT.git
• Go in the project folder cd ScreenRecorderQT/ScreenRecorderLegacy
• Generate the Makefile qmake ScreenRecorderLegacy.pro
• Compile it make clean; make all
• Allow the binary to be executed chmod 777 ScreenRecorderLegacy
• Run it ./ScreenRecorderLegacy with arguments, an example may be ./ScreenRecorderLegacy 700 700 0 0 0 30 1 5 1 hw:1,0 out.mp4

Troubleshooting

• In some cases installing c++ 20 won't be enough to compile the application and the libraries. You will have to add manually -std=gnu++2a in the CXXFLAGS of the **Makefile ** generated by the qmake command.
• If the application return an error related to the video device when you start the recording it could be caused by the DISPLAY environment variable. Try to export a new DISPLAY variable with the command export DISPLAY=:1. Sometimes (especially in VM) the DISPLAY variable contains the screen number and looks like :1.0 but this library is expecting a DISPLAY variable which look like :1 (only the Xserver) without screen number.

Windows

How to compile and run

Legacy application

• Download Qt 5.15 or higher version.
• Open with Qt Creator the file ScreenRecorderLegacy.pro that you can find in the folder ScreenRecorderLegacy.
• Let Qt choose the best kit configuration. The default version provided should work just fine, but in case you need to know what has been used:
  • Device type: Desktop
  • Compiler C++: MinGW (C++, x86 64bit in C:\TDM-GCC-64\bin)
  • Debugger: System GDB at C:\TDM-GCC\bin\gdb.exe
  • Qt version: Qt 5.15.2 (mingw81_64)
  • CMake Tool: CMake 3.19.2 (Qt)
• Once the project is open, please click on "Project" in the side bar.
• You will be able to see "Run" option on the left (Build & Run section). Click on this option.
• Explicit the command line arguments in the field. An example may be 700 700 0 0 0 30 1 5 1 "Microphone (Realtek High Definition Audio)" ../outFolder/out.mp4.
• Check the "Run in terminal" option.
• Finally, run the application using the green button. You will see the terminal pop up.

QT application

• Download Qt 5.15 or higher version.
• Open with Qt Creator the file ScreenRecorderQT.pro that you can find in the folder ScreenRecorderQT\ScreenRecorderQT.
• Let Qt choose the best kit configuration. The default version provided should work just fine, but in case you need to know what has been used:
  • Device type: Desktop
  • Compiler C++: MinGW (C++, x86 64bit in C:\TDM-GCC-64\bin)
  • Debugger: System GDB at C:\TDM-GCC\bin\gdb.exe
  • Qt version: Qt 5.15.2 (mingw81_64)
  • CMake Tool: CMake 3.19.2 (Qt)
• Finally, run the application using the green button. You will see GUI pop up.

Mac OS

How to compile and run

Legacy application

• Clone or Download the repository in a folder
• Install the required libraries with Homebrew packet manager brew install ffmpeg
• Open a new Terminal on /ScreenRecorderLegacyMacOS/folder
• Execute the following command
  • cd build
  • cmake ..
  • make
• Make sure you are still in the build folder. Now you can lanch the ./main executable file with the right options to start recording
• ./main width height offset_x offset_y screen_num fps quality compression audioOn audioDevice outFilePath
• Example ./main 3600 2338 0 0 1 30 1 1 1 0 out.mp4
• You can find the screen_num value and audioDevice value by digiting from terminal the following command:
• ffmpeg -f avfoundation -list_devices true -i ""