Background video / video does not work

Hie there. I’ve been trying to have a background video working for 2 hours ! but I always have a blank space (in preview mode or in Safari) !
the video is 11MO , in mp4 and when I handcode a html5 file it is working perfectly !
I put a code bloc and insert my own code and it eventually works.
What’s wrong with Bloc ?

Don’t have any problems doing it in blocs. Works fine for me.