If you go to here:

concrete/blocks/video/view.php

And copy that file to:

application/blocks/video/view.php (or make it a different name, for example no_controls.php to make it a new template you select, so don't forget to apply the template to your block on the page if you chose this way). Now, search for this:

controls="controls"

Remove that bit of code to remove all the controls for the video. Save the file and refresh. All your controls should be gone!

Thanks for this!

There was a couple of extra things I had to do, to make it work.
Turn off 'override cache' in settings, and make an extra directory called 'templates' so the structure looks like this: application/blocks/video/templates/no_controls.php

Love it!