Explain RTSP: how the streaming control protocol works and where it fits in live video

You are interviewing for a product manager role at Twitch, and the interviewer asks a technical question: what is RTSP, the Real Time Streaming Protocol? Explain what the protocol is for and how it works, at a depth that would let you discuss it with the engineers on a video team. ```hint Trace one session Follow a single viewing session from the moment a player is handed an rtsp:// address until it stops, and note which protocol carries each part of what is exchanged. ``` ### Clarifying Questions - Should I pitch the explanation for an engineering partner, down to the message level, or for a non-technical stakeholder? - Do you want RTSP on its own, or also how it compares with the protocols a live-streaming service uses to receive broadcasts and deliver them to viewers? - Should I cover where RTSP shows up in practice, such as IP cameras and surveillance systems? ### What a Strong Answer Covers - What RTSP is responsible for, and what it leaves to companion protocols for describing the stream and carrying the media. - The lifecycle of a session: the main requests, how session state is kept, and how the media transport is negotiated. - Transport options and their consequences for latency, firewalls and NAT. - Where RTSP is a good fit, and why it is a poor fit for delivering live video to large browser audiences. - Why a product manager at a live-streaming company should care, for example when deciding which stream sources or playback paths to support. ### Follow-up Questions - Why do large live-streaming services deliver video to viewers over HTTP-based adaptive streaming rather than RTSP, and what does that choice cost in latency? - A creator wants to stream directly from an IP security camera that only offers an RTSP feed. What would it take to support that, and would you prioritize it? - How do RTSP, RTMP and WebRTC differ in the problem each was designed to solve?