Your browser has no ability to Direct Play an MPEG-2 stream - or AC3 5.1.
Try this instead:
Here’s the New Player for Windows:
https://www.plex.tv/media-server-downloads/?_ga=2.116220037.2046312671.1561485849-1864473727.1455657109#plex-app
Kinda Buggy, but they’re working on it.
(Note: I am watching a recording with an MPEG-2 stream / AC3 2.0 audio on the New Player ATM and it is in Direct Play).

Still, for me, at this time, Plex Media Player is more stable.