Problem when downloading some youtube videos with PHP

I have some problem with my (https://smanegeri1sindang.sch.id/vdown) youtube downloader website.

First, when i enter https://www.youtube.com/watch?v=exXNEDZDuwc like the image in below

Fisrt image

The size is not showing and i can't download the video.

But when i enter second link https://www.youtube.com/watch?v=6SHAKxIBuH8 . It's working properly like the image in below

Second image

So, my question is how can i do to resolve the problem ? What can i do ?

My source code is available in https://smanegeri1sindang.sch.id/vdown.zip

Thanks a lot :)