Why does youtube api work on site but not locally?

Question

YouTube

There is such a codepen with an example background video from youtube. It is working. If you copy everything and try to open it locally, through the file system, then the video does not load. But if you upload the same files to any hosting - everything works. Here is the archive with the files. What could be the problem?

Answer 1

I got the impression that the whole thing is about copyright, to which YouTube is very attentive.
If you replace the video with any where there is no licensor for music tracks, then everything is played locally. If the licensor is specified, then the video is not played.
All videos you use have the copyright holders of the music.