RTSP: The Real-Time Streaming Protocol Explained (Update)

The Real-Time Streaming Protocol (RTSP) is a time-tested video technology. It’s used to control audio/video transmission between two endpoints and facilitate the transportation of low-latency streaming content across the internet.

   

Along with the Real-Time Messaging Protocol (RTMP), RTSP once dominated the streaming landscape. That’s no longer the case today. Nevertheless, RTSP remains a cornerstone in many security and surveillance architectures, particularly in closed-circuit television (CCTV) systems. The reason is simple: it’s still the preferred protocol for IP cameras.

In this article, we’ll delve into the RTSP specification, explore its history, and outline common workflows utilizing this protocol for real-time video streaming applications. 

 

What Is a Protocol?

Protocols establish rules for data transmission between systems. For example, the Hypertext Transfer Protocol (HTTP) defines how webpage data and hyperlinks are transmitted across the internet, enabling seamless browsing.

Similarly, streaming protocols govern the delivery of live and on-demand content. These protocols function for both ingest (first-mile) and egress (last-mile) transmission. RTSP plays a key role in real-time video streaming architecture ,orchestrating sessions between a source and a streaming server. 

What Is RTSP?

RTSP is an application-layer protocol used for commanding streaming media servers via pause and play capabilities. It thereby facilitates real-time control of the streaming media by communicating with the server — without actually transmitting the data itself. Rather, RTSP servers often leverage the Real-Time Transport Protocol (RTP) in conjunction with the Real-Time Control Protocol (RTCP) to move the actual streaming data.  

 

The official 1998 RTSP standard states::

“The Real-Time Streaming Protocol (RTSP) establishes and controls either a single or several time-synchronized streams of continuous media such as audio and video. It does not typically deliver the continuous streams itself, although interleaving of the continuous media stream with the control stream is possible. In other words, RTSP acts as a ‘network remote control’ for multimedia servers.”

 

When a user initiates a video stream from an IP camera using RTSP, the device sends an RTSP request to the streaming server, initiating the setup process. Subsequently, RTP transmits the audio and video data. Think of RTSP as a remote control for media streaming, while RTP handles the actual broadcast. 

 

RTSP: A Snapshot

• Audio Codecs: AAC, AAC-LC, HE-AAC+ v1 & v2, MP3, Speex, Opus, Vorbis
• Video Codecs: H.265 (preview), H.264, VP9, VP8
• Playback Compatibility: Not widely supported and rarely used for playback (Quicktime Player and other RTSP/RTP-compliant players, VideoLAN VLC media player, 3Gpp-compatible mobile devices)
• Benefits: Low-latency and ubiquitous in IP cameras
• Drawbacks: Not optimized for quality of experience and scalability
• Latency: 2 seconds
• Variant Formats: RTSP as an umbrella term describes the entire stack of RTP, RTCP (Real-Time Control Protocol), RTSPS (RTSP over SSL / Secure RTSP), and good-old RTSP

 

RTSP Commands

RTSP employs various commands to control media streams. These include:

• Options: This request determines what other types of requests the media server will accept.
• Describe: A describe request identifies the URL and type of data.
• Announce: The announce method describes the presentation when sent from the client to the server and updates the description when sent from server to client.
• Setup: Setup requests specify how a media stream must be transported before a play request is sent.
• Play: A play request starts the media transmission by telling the server to start sending the data.
• Pause: Pause requests temporarily halt the stream delivery.
• Record: A record request initiates a media recording.
• Teardown: This request terminates the session entirely and stops all media streams.
• Redirect: Redirect requests inform the client that it must connect to another server by providing a new URL for the client to issue requests to.

Other types of RTSP requests include ‘get parameter,’ ‘set parameter,’ and ’embedded (interleaved) binary data,’ which are detailed here.

 

Typical RTSP Workflow

RTSP is a stateful protocol used more often for video contribution (ingest) than for last-mile delivery and playback (egress). Android and iOS devices don’t have RTSP-compatible players out of the box, for which reason RTSP is rarely used for streaming from end to end. Instead, most broadcasters leverage a streaming server like Wowza to repackage the RTSP stream into a more user-friendly format like HLS.

 

History of RTSP Streaming

RTSP was developed in the late 1990s by Netscape Communications, Progressive Networks (RealNetworks), and Columbia University. The Internet Engineering Task Force (IETF) officially published it in 1998, with Version 2.0 introduced in 2016 to optimize session communication. 

Before adaptive bitrate streaming (ABR) via HLS (HTTP live streaming)and MPEG-DASH (dynamic adaptive streaming over HTTP), RTSP and RTMP dominated the live streaming space. However, due to their reliance on dedicated servers, they were not suited for large-scale streaming. 

As such, RTSP is now used primarily as an ingest protocol, meaning it is typically only used in the first part of the streaming workflow before the streams are transmuxed into for delivery. Most workflows leverage a media server to ingest streams transmitted via RTSP/RTP and then repackage the file for delivery to viewing devices — ranging from iPhones to smart TVs.

Next-generation alternatives like Secure Reliable Transport (SRT) are competing directly with RTSP for video contribution today. Even so, RTSP remains popular in surveillance workflows as the de facto standard for IP cameras.

RTSP vs. Alternative Ingest Formats

If you’re looking to swap out RTSP for a proven alternative, RTMP is the most popular protocol used for first-mile contribution today. In fact, a whopping 76.6% of respondents to our 2021 Video Streaming Latency Report indicated that they use RTMP for ingest.

As shown below, Web Real-Time Communications (WebRTC) and SRT are also popular formats, with only 18.6% of content distributors today relying on RTSP.  

 

Which streaming formats are you currently using for ingest?

Here’s a look at how the three options compare.

 

RTMP

RTMP is RTSP’s oldest rival, and it’s a better choice if streaming directly to a social media platform. Both protocols are used for contribution, but more encoders and live streaming services accept RTMP.

Facebook, Twitch, and YouTube — for instance — only accept RTMP for low-latency live streaming. That means you’ll either want to encode your stream as RTMP from the get-go, or repackage any RTSP streams as RTMP using a video platform provider like Wowza. The latter option would also enable simulcasting to multiple destinations at once, making it a good route for those looking to live stream from an IP camera to social media.

 

SRT

As an open-source technology optimized for unpredictable networks, SRT promises to displace RTSP and RTMP once widely supported. Encoders and media servers are still adding support for SRT, and streaming services like Facebook could very well follow.

In a recent Wowza LinkedIn poll, SRT generated the most interest for first-mile contributions. The protocol is also optimized for unpredictable public networks — combining speed and reliability into a single solution.

 

WebRTC

WebRTC is the speediest technology available right now, delivering near-instantaneous voice and video to and from any major browser. It’s also the only answer if simplicity is key. Unlike RTMP, RTSP, and SRT, WebRTC can be streamed from end to end, without additional processing.

WebRTC used to be restricted to small-scale streaming and browser-based publishing, but that’s all changing. A technology called the WebRTC HTTP Ingest Protocol (WHIP) provides encoding software and hardware with a standard signaling protocol when talking to media servers, thus removing WebRTC connectivity barriers between encoders and media servers. And Wowza’s  Real-Time Streaming at Scale feature for Wowza Video supports WHIP, as well as streaming to a million viewers.

Using Wowza as Your RTSP Server

Despite its age, RTSP has staying power as an ingest format. But — to drive it home once more — you’ll need a video repackaging solution to deliver the stream to end-user devices.

RTSP servers allow you to convert live RTSP streams into another format for playback. A media server software or service can be used to achieve this and more. For instance, you may want to repackage your RTSP stream into HLS for large-scale delivery, or perhaps you want to use WebRTC to maintain sub-second delivery.

 

IP Camera Streaming: Highlight on RTSP to WebRTC

RTSP and IP cameras are closely linked. A media server typically retrieves the RTSP stream from the IP camera, transmuxes it, and delivers it in a playback-friendly format. 

For real-time surveillance, RTSP-to-WebRTC workflows are popular due to sub-second latency. See our tutorial for setup guidance here . 

 

Choosing Wowza

Wowza provides a comprehensive, scalable streaming solution. Whether you need a media server for ingest, transcoding, or delivery, Wowza has you covered. Start with a free trial today