Real Time Streaming Protocol (RTSP) is an application-level network communication system that transfers real-time data from multimedia to an endpoint device by communicating directly with the server streaming the data.
The protocol establishes and controls the media stream between client devices and servers by serving as a network remote control for time-synchronized streams of continuous media, such as audio and video. It does not stream the multimedia itself but communicates with the server that streams the multimedia data. When a user pauses a video they are streaming, for example, RTSP conveys the user’s request to pause the video to the video streaming server.
When a user or application attempts to stream video from a remote source, the client device sends an RTSP request to the server to determine the available options, such as pause, play and record. The server then returns a list of the types of requests it can accept through RTSP. Once the client knows how to make a request, it transmits a media description request to the streaming server, and the server responds with a description of the media. From there, the client sends a setup request, and the server responds with information about the transport mechanism. Once the setup process is complete, the client initiates the streaming process by telling the server to send the bitstream — a binary sequence — using the transport mechanism specified in the setup request.
RTSP started as a way to allow users to play audio and video straight from the internet, rather than having to download media files to their devices. The protocol has been applied for various uses, including internet camera sites, online education and internet radio.
RTSP uses the same concepts as basic HTTP, which makes it easily compatible with existing HTTP networks. The protocol also allows for a great deal of flexibility. Clients can request the features they want to use in an effort to find out if the media server supports them. Likewise, whoever owns the media can deliver media streams from multiple servers. The protocol is also designed to accommodate for future growth of the media so the media creator can amend the protocol moving forward if necessary.
RTSP has a number of key components, including:
RTSP is based on a 1997 proposal written by Anup Rao of Netscape Communications — later renamed New Aurora Corp. and sold to Facebook — and Rob Lanphier of Progressive Networks — now known as RealNetworks. The Multiparty Multimedia Session Control (MMUSIC) Working Group of the Internet Engineering Task Force (IETF) published it as Remote Function Call 2326.
Rao, Lanphier and others proposed RTSP Version 2.0 as RFC 7826 in December 2016. This version introduced some new header values in an effort to shorten the roundtrip communications with the media server. Version 2.0 also addresses some of the issues associated with Network Address Translation (NAT) traversal.
The components below comprise the technicals details, benefits, and drawbacks of the RTSP streaming protocol:
Direct RTSP streaming is not supported by browsers. You can use a proxy server that will convert RTSP to an HTTP stream as a workaround if you have to play an RTSP stream in a browser.
Pull; most IP cameras use the RTSP protocol to pull data to the media server.
RTSP uses the Real-time Transport Protocol (RTP) with Real-time Control Protocol (RTCP) to deliver media streams.
RTSP does not support content encryption because RTSP is connected to a dedicated server for streaming and relies on RTP to transmit real media. This major limitation led to a drop in RTSP usage.
RTSP uses a Transmission Control Protocol (TCP) connection, but it is also possible to use UDP.
While RTSP has not been able to keep up with the popularity of other streaming protocols and has major disadvantages compared to them, RTSP remains standard in many surveillance and closed-circuit television (CCTV) architectures.
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