Having the same issue. hhttps://www.mata-architects.co.uk/
The video is blurry first the first few seconds and then switches to the original quality.
The video is used as the background image for a cover page in 7.0 Forte template.
We upgraded to from embedded Youtube and got a Vimeo Plus account in order to get this to work cleanly for our homepage.
Also tried adding a default quality to the embed but there is no change:
https://vimeo.zendesk.com/hc/en-us/articles/224983008-Setting-default-quality-for-embedded-videos