Low Internet download speed

As I started to stream videos, my internet started to buffer in every 5 seconds!!!  Works 5 seconds and continues to buffer about 15 seconds... and repeat..

I checked my internet speed with speed.net and found out that I have download speed of 48 MBps and upload 10MBps.  I am subscribed for 100MB download!  Could you please explain why I am not getting the expected value.  I did not subscribe to the 50MB download!

I appreciate any help and expect that the cox technical experts provide resolution to the issue...

Thanks,

Ken