youtube-dl only video code example
Example 1: youtube-dl best quality
youtube-dl -f bestvideo+bestaudio/best https://www.youtube.com/watch?v=nYdiDq1fOiM
Example 2: downloading youtube playlists using youtube-dl in highest quality
youtube-dl -f best 'http://www.youtube.com/watch?v=P9pzm5b6FFY'