Have a look at the 'Migrating Eels' video Lake Bolac Caravan Park If that's what you're after, here's the code I used in the 'Body' section of the placeholder:
<video controls="controls" loop= "true" width="100%" height="100%"
<source src="https://lakebolac.holiday/MigratingEels.mp4" type="video/mp4" />
I also downloaded your video from YouTube at 640x360 and it was acceptable at full screen, size 37.2MB. If you used the same code as above but remove the loop part you should be good to go.
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