I am also a media creator with many years of experience. 

What is the Bitrate of the video, what is the upload bandwidth of the server you are hosting it from? 

This doesn't look like a problem with nostr. It looks like a problem with your media server. 

You can try vlc and use the url you gave. Same issue with buffering and stalling. 

YouTube has a very efficient media streaming platform with multiple quality versions of the media, testing of your speed and adapting the media served.