For a few weeks, I had a bug where I couldn't play any video content in MSEdge, and thought it was just because I was on the canary channel. I thought the bug would resolve itself, but after a while, I realized that something must be wrong as I was the only one experiencing the bug.
After thinking about it some more, and getting really fed-up that I couldn't watch videos of any sort (from Reddit, YouTube, Twitter, etc), I decided to look at the flags I had enabled to see if any of them were causing the issue, and low and behold, disabling this one did the trick.
If you like to enable flags to test new features: DON'T ENABLE THIS ONE! Something about it ruins Edge's ability to play video content, and just shows a black screen instead of the video.
If you know what it does, or you're testing the flag, power to you! Otherwise, just stay away from it.
Enjoy the new Edge experience! I'm excited to see these new vertical tabs.... Seems like an interesting idea....