Free Screen Recorder Pro uses the source code of Captura by MathewSachin which is open-source project under license MIT.
FFmpeg website: https://ffmpeg.org/.
The Captura's official website:
-Capture ScreenCasts (Avi/Gif/Mp4)
-Capture with/without Mouse Cursor
-Capture Specific Regions, Screens or Windows
-Capture Mouse Clicks or Keystrokes
-Mix Audio recorded from Microphone and Speaker Output
-Capture from WebCam.
-Available in multiple languages