Right, first of all are you connected wirelessly? If so, plug directly into the router using an ethernet cable and re-test.
Have you tried restarting your computer? Have you tried restarting the router?
Do you experience this problem on all video streaming sites? Try a few out.
Now, if you want to get a bit more technical...
If you're on Windows, click on Start, go to Accessories and click on Command Prompt. Do this three times, so you have three command prompt windows open.
In the first one, type the following and press Enter:
ping
www.bbc.co.uk -t
Then on the second one type and press enter for:
ping 127.0.0.1 -t
The next one is a bit more complex, we need to ping your router.. which is likely to either be 192.168.0.1 or 192.168.1.1 - it could be something else, but it's different for different routers. To find out, type "ipconfig" and press enter. Then look for your "ipv4 default gateway".
So the third command will be (assuming it's 192.168.0.1)
ping 192.168.0.1 -t
So now you'll be running connection tests to somewhere on the internet, your own computer (loopback) and your router. Now if you position these three windows so you can see them all, look for anything where it says Timed out or destination host unreachable, etc. Anything that looks bad really! Also look out for high numbers for the ping times (latency/lag)
Basically, if you see this happening on the 127.0.0.1, it means you likely have a problem with your network card on your computer. If you see it on the router IP, your connection is dropping data to the router before it's even reached the internet. If it's happening to bbc.co.uk then you know it's a problem on the internet side of your router and beyond.
Now I don't know if that's way too technical or not, but might help
