How to understand the difference between the two online video: RTSP and HTTP?

RTSP stands for Real Time Streaming Protocol. One of the main uses for RTSP is to receive streaming video (e.g video on demand). A client establishes a connection with a media server and obtains data from the server and displays it.

HTTP, on the other hand, is a stateless protocol. HTTP provides a mechanism to download a media file over the internet. It would not be wrong to think of accessing media over HTTP as accessing a file over a network and playing it.