YouTube Video Downloader

A Tkinter program that downloads YouTube videos using Pytube, FFmpeg-Python and Threading.
Audio Only files are downloaded in mp4, then converted to mp3.
144p files are downloaded in 3gpp.
720p and 360p files are downloaded in mp4.
Other files are downloaded video only in mp4, then concatenated with an mp4 audio file.
The result is in mp4.
To run the program, you need a Python 3 interpreter, ffmpeg-python and pytube modules installed by using pip.