Well, i don't know if this is quite the website for this kind of subjects, but let's get on topic ^^
It really depends on the origin of the stream, many stream providers have a different way of delivering the video with different encryption aswell, so you would really have to be more specific... But you could probably google it anyway...
A solution that would always work is some screencapture software, but it's hard to find something that offers proper quality.