We can not fetch videos from this type of page.
Your URL was: http://save-video.mp4?http%3A%2F%2Fwww%2Eyoutube%2Ecom%2Fget%5Fvideo%3Fvideo%5Fid%3DUem36yQ5dR4%26t%3DvjVQa1PpcFNSO4a2hdzlOwxMZv4X3uTPAb4qZgiIlwQ%253D%26fmt%3D18
The URL must be like http://www.youtube.com/watch?v=KPtX7hak0Qs
https://www.
and replace with pwn
Example: