The Real Time Streaming Protocol provides control operations for media sessions, such as requesting playback or stopping a session. It is separate from the media content and from the transport used to carry that content. A supported RTSP address therefore needs a compatible server, player and underlying media arrangement to work.
A practical example
A camera viewer can send a playback request to an RTSP server and then receive the resulting media through an agreed transport. The control conversation and the video packets perform different jobs, even when the application hides that distinction.
A common misunderstanding
Changing the beginning of a URL to RTSP does not convert another stream format. A server must actually implement the protocol and expose a valid resource for the player.
Related terms
Further reading
Stable technical definition. Editorial approach