Recently, my Internet has been suffering from this problem and I can't watch any videos even in 480p -sometimes 360p-. I discovered this when I went into router interface. I opened the log page and saw that I've been getting DoS ICMP flood attacks. So, I cleaned my computer from viruses with Malwarebytes and HitmanPro -that was suggested to me at another forum-. I'm getting tons of attacks and we have a FUP (Fair Usage Policy) -a bandwith cap- in our country and these attacks literally eats my bandwith. What shall I do? Thanks for the help already and sorry for my English if I made any mistakes.
In your router, I would look for a setting that is something like "Don't respond to ping requests from the WAN", which literally means "Ignore ICMP requests from the internet". It should be in the firewall section of your router.