What is Real Time Streaming Protocol (RTSP)

Streaming has become a popular convention across multiple platforms. It’s a great way to present visual information that educates, informs, and entertains. Streaming has emerged as a fantastic online medium because it’s scalable and users can capitalise on the increased network bandwidth they have access to.

Live streaming is more commonplace than ever before, where the ease of setting up a camera and orchestrating what is essentially a push-button operation has increased the realm of possibility for users across the globe. The emergence of easy-to-use streaming platforms and media servers has incentivized a generation of streamers who set up live videos for different purposes.

With the advancement of Internet Protocol (IP) cameras, users can stream/record live video without having to operate their camera in real time. The self-sufficient nature of IP cameras, combined with the ability to record and send data via the internet, gives the broadcaster maximum control.

IP cameras are commonly used for:

• Classrooms/lecture theatres
• Traffic footage
• Security cameras
• Events
• Personal home security

When something is recorded via an IP Camera, the data is transmitted using Real Time Streaming Protocol (RTSP).

But what exactly is RTSP and why is it so important to the streaming experience?

Table of Contents:

• What is Real Time Streaming Protocol?
  
• What is the RTSP Protocol?
• What’s the Difference Between RTSP and RTMP?
• What is RTSP to WebRTC?
• RTSP: A Look Under the Bonnet
• What is Adaptive Bitrate Streaming?
• Conclusion

What is Real Time Streaming Protocol?

Real-Time Streaming Protocol (RTSP) and Real-Time Media Processing (RTMP) used to be the main systems for regulating, formatting, and processing media streams. However, the main downfall with these governing rules is they require a dedicated server and tend to not function as well with large-scale broadcasts.

In today’s advanced streaming age, RTSP is predominantly used to transmit streams from IP cameras. The great thing about IP cameras is they don’t require a local recording device, meaning you can stream live footage via a local network. This makes IP cameras the perfect digital security camera solution because they receive footage and then send it to a network, not a physical location. It is during this data transmission process that RTSP is commonly used as a contribution protocol. With the right media server in place, streams can be repackaged so they’re viewable across multiple devices.

Now that you’ve established what RTSP is and its general use purposes, let’s delve a bit deeper into the protocol…

What is the RTSP Protocol?

RTSP started out as a way for users to enjoy audio and video content online without having to download files to their devices. It represented the evolution of online content consumption, where being able to stream via the internet was a revolutionary concept.

In today’s landscape, adaptive bitrate streaming via HTTP-based protocols is more commonly used because they don’t require dedicated servers. However, RTSP hasn’t lost its relevance. For as long as IP cameras are prominent recording devices, RTSP can be applied within many contexts.

What’s great about RTSP is its ability to effectively transmit audio/video from one source to another. For example, if you have an IP camera set up recording the front of your house, RTSP can help to transport low-latency content across the internet so it can be played back on a device of your choice.

As a protocol, RTSP represents a set of governing rules for communicating information from one system to another. Hypertext Transfer Protocol (HTTP) works in a similar way, where links and web page data are transmitted across the web using governing systems between browsers and web servers.

RTSP delivers live streaming content as a foundational technology that coordinates information between the source and the streaming server. It facilitates streaming via communication with the media server you have in place. This is beneficial because the data itself doesn’t need to be transmitted, just the actual streaming data for convenient access at your leisure. When you set up an IP camera via RTSP, it will communicate with the streaming server and transmit audio and video data for consumption.

What’s the Difference Between RTSP and RTMP?

Real-Time Messaging Protocol (RTMP) is a technology that works in conjunction with Transmission Control Protocol (TCP). Like RTSP, it was initially developed to real-time stream audio, video, and other data. Its compatibility with TCP enables advanced communication between the recording device and the server where data is transmitted. This means that the user can enjoy a consistent, reliable stream via their recording device.

RTMP is commonly used as a protocol for live-streaming platforms. It converts streams into playable formats by taking advantage of low-cost encoders. RTSP and RTMP share many common characteristics and are not in competition with each other. The decision to use one over the other depends on the demands of your platform and streaming operation in general.

What’s great about RTMP and RTSP is they’re both low-latency and can control media streams by delivering media on demand, in real-time via a stable connection.

However, RTSP is perfect as a cheaper, simpler streaming alternative. It developed significantly due to its widespread use by engineers when RTMP was walled off as a proprietary technology. As previously mentioned, RTSP is the standard with most IP cameras. It’s great for localised streams and as an input for conferencing or monitoring systems.

What is RTSP to WebRTC?

Though RTSP is incredibly useful, it isn’t without its setbacks. Streams must be repackaged for more friendly playback, but unfortunately, this can result in latency issues that can cause delays and generic lags. Given the critical use of IP cameras in highly-important surveillance situations, it’s essential you can overcome latency issues to promote clear, crisp playback where you can identify what’s happening on-screen.

One of the best ways to secure better video delivery is to use Web Real-Time Communications (WebRTC). This has transcended the streaming landscape by converting RTSP feeds into real-time streams that display in clear quality without playback issues.

WebRTC is compatible with most browsers and maintains sub-second delivery. It provides a more consistent viewing experience than RTSP, which on its own can cause up to 20 seconds of latency.

WebRTC works by restreaming content from RTSP. Its application underlines the importance of working with an effective media server, which will ingest your IP camera stream and repackage it into WebRTC. You can then access your web-hosted playback page URL at your leisure.

RTSP: A Look Under the Bonnet

RTSP uses commands to send requests from the client to the server. This is all part and parcel of controlling and negotiating media transmissions.

RTSP uses the following commands:

• Options
• Announce
• Describe
• Setup
• Play
• Pause
• Record
• Teardown
• Redirect

These are coordinated to present the media in its best possible form. When data is transferred and repackaged across the server, users can access content via a link that’s generated. The ability to play back files on demand, without them having to be physically stored on your device, is one of the biggest reasons why RTSP will continue its prominent role within the streaming world.

RTSP uses the following audio and video codecs:

• AAC, AAC-LC, MP3, Speed, Vorbis, Opus, & HE-AAC+ v1 & v2
• H.265, VP9, VP8, H.264

As a protocol system, it’s rarely used for playback because it’s not formatted to create a physical file that’s played on a device. However, it is compatible with Quicktime Player, 3Gpp-compatible mobile devices, and VLC media player.

It’s great for low-latency streaming but isn’t optimised for quality of experience and scalability. For this reason, adaptive bitrate streaming is widely used in other contexts, especially when IP cameras aren’t in operation.

What is Adaptive Bitrate Streaming?

Real-time streaming has evolved significantly since its inception. Though newer technologies like adaptive bitrate streaming have emerged, RTSP retains its position as a vital protocol for essential streaming functions.

RTSP resembles HTTP in operation, so remains compatible with HTTP networks. The rise in prominence of adaptive bitrate streaming and other HTTP-based progressive technologies have eclipsed RTSP in many streaming environments.

Adaptive bitrate streaming is more suitable in most streaming contexts because streams don’t have to be repacked into protocols like HTTP Live Streaming (HLS). The process improves streaming over HTTP networks and occurs during the encoding stage of video production. This is when videos are converted into a format that can be used on multiple devices.

Adaptive bitrate streaming allows videos to be segmented into smaller components. When videos are streamed by the viewer, video files are transferred from the server to the person who’s viewing the content. When videos are segmented into smaller clips, the viewer won’t have to wait for an entire video to load before they can start watching it.

Without segmentation, the entire video file would need to be downloaded before it could be played. What makes adaptive streaming so important to streaming is it gives users a chance to stream content at a bitrate their device/internet connection can handle. The video player will determine what level of bitrate can be accessed based on current conditions. It will find the highest one the user can handle, meaning streamers can release content for a wide-ranging collection of users across a wider pool of available viewers.

Conclusion

Adaptive bitrate streaming encodes files so that the viewer can find an ideal match for their connection. Though its popularity across YouTube and other online platforms is widespread, RTSP has established and will retain its relevance for as long as IP cameras are prevalent.

RTSP will continue to be used for ingesting media as the first port of call for a larger streaming workflow. It differs by approach because it sends commands rather than transmitting actual stream data.

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