I've had conversations with our head IT guy at my fairly big firm, and he hates spying on people. So he doesn't do it. Unless you make him, by impacting the ability of the network to be used by others. So video and audio streaming is a bad idea here. You don't want to draw attention to yourself. I'll occasionally watch a short youtube video, but I need to stop doing that. We have about 1000 employees in this office and if they all jumped on youtube or opened spotify, the system would screech to a halt. Our pipe is big, but not that big.
I've had to have conversations with people in my department who got caught downloading and/or streaming entire feature length movies. IT freaks out when people do that. They especially freak out when you save a few of them to a network drive.
But yeah, IT can monitor everything if they want.