So, I really don’t like the video player that Blocs has, so I have been looking for an alternative (besides embedding from other hosting services like YouTube/Vimeo).
I’m limited on time to help, but I’d first look at how you are referencing the video file. Try using the Bloc shortcodes (see documentation) could help you get the correct path.
If I just enter the code into an html bric and id it as per the instructions (the bloc not the code widget) without adding any code to the header then I get a preview of my designated video on the page within the script snippet but again it fails on the browser preview. So the source address works - therefore it must be something else?