Failed to load video in live preview - error 513


I’m working on a simple static site mockup in an SSH workspace - it’s connected to a Digital Ocean droplet here:

I’m loading in an .mp4 video as a hero background.
It works fine on the live site - in the address listed above - but I can’t see the video in the c9 Live Preview.

I’m getting the following error in the JS console:
“Failed to load resource: the server responded with a status of 513 (unknown)”

Any ideas why the video wouldn’t load? Maybe a codec issue?
Thanks in advance for your time,