Hi @aaronge and thank you for your reply.
I submitted a ticket but I still have the same problem. The answer is confusing, they are not offering any solution. The format is mp4 and I tried different sizes: 480p, 720p, 1080p and different MB - from 9 to 52 MB. Videos still look blurry, I really don’t know how to go on with my portfolio. 
This is the ticket number: 1847934900
Any little help is much appreciated.
Thank you
Mara