I usually download youtube videos by inserting 'ss' in the video link like this:
https://www.ssyoutube.com/watch?v=graJ_KjK-yg
This method is commonly known to people.
But, when I did like above, it says, "The download link not found."
I don't know why but some videos are not able to be downloaded using the above method.
I found an alternative.
youtube-dl
https://github.com/ytdl-org/youtube-dl
This method is basically wonderful to download a playlist of youtube videos
You can find how to use the tool. It supports Windows, Linux, and Mac.
I just executed like this: (I am using Ubuntu)
$ youtube-dl https://www.youtube.com/watch?v=graJ_KjK-yg
You see I put the same link which was not found in savefront.net.
Here is the screenshot of downloading!
It is awesome!
When you want to download a playerlist of so many videos, the tool is right for you.
Enjoy the tool.