Most of the common protocols for streaming video involve making a series of http requests to fetch short segments of video from a server. If there wasn't pipelining or QUIC requests going on it would be pretty obvious what was going on, but maybe less so if the requests were spread out across a number of servers.

With pipelining or some other protocols the signature is going to be a sustained download that runs at a rate less than the maximum possible.

If the servers are being found through DNS that's another tool to figure out what is going on. If not, the carrier is going to want a list of IP blocks associated with video streaming.

What I don't get is customers caring a lot about whether they are getting 480p vs better. The old NTSC video was outright awful, and the difference between that and 480p is greater than that between a clean 480p and 720p, 1080p or even 4k. In the best circumstances the returns are diminishing but if you are viewing on a little phone screen in bright light what's the point?