Hi @Ricardo, currently the link you provided was to the https location of the file. Could you point your url at the non-https location of that dropbox file to see if it makes a difference? You can use a dropbox link from a file uploaded to your public folder, but when inserting that link into the embed block, you need to be sure to remove the ‘s’ from ‘https’ - otherwise you’ll see a black background and the video won’t load.
I hope this helps, let me know 
Cheers, Dave