Download your youtube video (Make sure you are in downloads directory so you can write the file!)
youtube-dl https://youtu.be/kJQP7kiw5Fk
You can paste with ctrl+alt+v into termux
You can pass the command –restrict-filenames to have clean file names without spaces for example: youtube-dl --restrict-filenames https://youtu.be/kJQP7kiw5Fk
Upgrade everything after it has been a while or when you encounter problems
pip install --upgrade pip youtube-dl
Updated 2020-04-07 to get ffmpeg from the archive and not pip.