Real-Time Streaming Protocol (RTSP) – The Ultimate Guide

Your viewers can pause, play, stop or record your live streams 📺just as they prefer. But, if you remove just one protocol from your streaming set-up, they might not be able to do any of these actions. 
And this protocol is RTSP – Real-time Streaming Protocol. 

The next 4 mins of this article is about RTSP.

If you think why you need to read about RTSP:

Any dysfunction of this protocol could have been a reason why your stream stopped, buffered, froze, or disconnected last time. And we are elaborating on the tech behind it to give a wider idea about this, before you launch your live streaming app. 

Let’s get started.

What is Real-Time Streaming Protocol (RTSP)?

Wikipedia describes the RTSP as an application-level network protocol that is responsible for multiplexing and packetizing multimedia data in a stream. 

It also adds that the protocol controls streaming media servers. 

Both of these statements clearly demonstrate that RTSP not only takes care of establishing data transfer like other protocols, but also takes control of the media streams. 

So, this is how we’d like to define RTSP, 

“RTSP (Real-time Streaming Protocol) is a set of rules that helps manage and control the flow of audio and video in a live stream.“

It allows you to start, stop, pause, and play the stream, ensuring smooth delivery of media between the server (where the stream comes from) and the viewer (who’s watching).”

Recommended Read: Top 10 White Label Live Streaming SDK & API Providers

Why RTSP: Properties Of This Streaming Protocol

Streamers and Streaming businesses choose to use RTSP for building their platform, for a lot of performance reasons. On the technical front, there are other things you must know about this protocol. This way, you’ll understand if it’s a good fit for your business or not. 

1. Transport-independent: There are a lot of protocols out there –  UDP, TCP, or even RDP and RTSP can work with any of them to transmit the streaming data between the client and the server. 
2. Secure: When it comes to security, RTSP supports basic and digest authentication methods of HTTP authentication. But for the majority of streaming platforms, this existing web security mechanism may not be sufficient. In these cases, developers go for additional security features. 
3. nd transport-layer firewalls, including SOCKS proxies. RTSP uses port 554 by default. If you are using a firewall or a router, you may need to open/forward port 554 to allow incoming traffic for the stream.
4. Custom ports: There are also cases where some servers might use non-standard ports. At these instances you must configure the network settings on your platform accordingly.
5. Separation of stream control and conference initiation: The way RTSP handles media streams and conferences will differ from each other. 
6. Capability negotiation: RTSP allows the client (like your media player) to check what features the server supports. It’s similar to how your smartphone might adjust its display based on the streams that will be displayed. 
7. Multi-server capable: RTSP can manage content that is coming from different sources simultaneously. For example, the protocol can handle a live sports broadcast where the video comes from one server and the commentary audio from another. Isn’t that interesting?
8. Presentation description neutral: RTSP doesn’t really care about the format for the media content description. But it will need a unique address (URL) to locate each piece of content. 
9. HTTP-friendly: RTSP borrows concepts from HTTP, making it easier to implement and integrate with existing web technologies. 
10. Extendable: The protocol is designed to grow and adapt. New features can be added without breaking existing functionality, similar to how apps can be updated with new features.
11. Easy to parse: RTSP uses a structure that’s familiar to web technologies, making it easy for existing tools to understand and process its commands.
12. Control of recording devices: RTSP can manage devices that play, record, or do both. 
13. Suitable for professional applications: RTSP supports precise timing, which is very important for professional video editing. 
14. Transport negotiation: Before starting to stream, RTSP allows the client and server to agree on how data will be sent i.e the packetization and transport protocol decision is made.
15. Appropriate server control: RTSP ensures that if a client can start a stream, it can also stop it. This prevents situations where content keeps playing without the ability to turn it off, like having both an on and off switch for any device you can turn on. 
16. Extensibility: While not explicitly designed for multi-client scenarios, RTSP allows for potential adaptation to such use cases, with stream identifiers that could be used across multiple control streams.

RTSP States You Must Know

OPTIONS:

This state allows the client to query the server’s capabilities. The client sends an OPTIONS request to find out which methods and features the server supports during the stream. This is very important to make sure that the client and server are compatible with each other before initiating any complex operations for the streaming process. 

DESCRIBE:

The client needs metadata about the media resource before it can start transmitting the streaming data. So it sends a quick request to the server. Eventually, the server responds with a Session Description Protocol (SDP) document, containing essential information such as media types, encoding formats, and timing details. 

ANNOUNCE:

ANNOUNCE is a bidirectional state serving two purposes:

• Client to Server: The client can publish media descriptions to the server that are typically used in broadcasting scenarios.

• Server to Client: The server can update session descriptions so that it can  make dynamic adjustments to stream properties in real-time.

SETUP:

During this state, the client and server negotiate the transport parameters. The client proposes a transport method (e.g., RTP over UDP), and the server either confirms or suggests a few other alternatives. 

PLAY:

The PLAY state initiates the actual media streaming on your app. The client can specify start and end times, enabling features like seeking or resuming from a specific point. Multiple PLAY requests can be queued which is very useful for advanced playback scenarios.

PAUSE:

This state temporarily halts media delivery without closing the session. The server maintains the current playback position, allowing for seamless resumption when it receives a PLAY request.

TEARDOWN:

The TEARDOWN state signals the end of the streaming session. It instructs the server to stop media delivery and release all the associated resources, effectively closing the RTSP session.

GET_PARAMETER:

Using this parameter, your client can retrieve specific session or media parameters from the server. It’s also commonly used as a keepalive mechanism to maintain session validity without affecting media delivery.

SET_PARAMETER:

In this state, the client can modify certain session or media parameters. It’s typically used for adjusting playback settings or updating metadata associated with the stream.

REDIRECT:

The REDIRECT state is used by the server to instruct the client to establish a new session with a different server or resource. This is often employed in load balancing or content distribution scenarios.

RECORD:

This state initiates the recording of streamed media on the server side. It’s particularly useful for applications like surveillance systems or archiving live broadcasts.

How Does RTSP Work?

1. Starting The Connection

• A viewer opens your streaming app and clicks on the ‘play’ button of your live stream. 
• Now, the device (let’s say a mobile) is the client. It sends an RTSP request to the server to start the media session. 
• What you should notice here is the RTSP request. The RTSP request differs from usual Client requests in other apps. How?
• We saw that RTSP controls the play, pause, stop and record options in a stream. 
• Now that the user has clicked ‘Play’ on the stream, it carries this information to the server, plus requests the server for the media metadata. 
• Since your viewer’s device is a mobile, it wants information about the format of the media, the protocol info to know how the media will be delivered and other meta-data about the live stream media. 
• This is the phase where your viewer might get the “video format unsupported” error if the client does not support the meta data. 

2. Server Confirmation

Once the server receives the request along with the description, it responds with all the necessary information including the transport mechanism (TCP or UDP) and session identifiers.

3. Starting Playback

The client receives the meta-data, checks the criteria and if everything is fine, it sends a command to start playing the video. 

4. Streaming Content

• Now, the server starts to send out the actual video data to the client in real-time. 
• All of these processes happen in microseconds, in such a way the viewer can watch the stream without any delay. 
• The one thing you must notice here is RTSP does not carry the data itself, rather it uses the RTP (Real-time Transport Protocol)to carry out the actual data delivery. 
• The process repeats for every option that the viewer uses on his mobile phone – pause, play, stop or record. 
• For every command, a request-response happens between the client and the server in real-time. 

Technical Components Of RTSP: For Streamers & App Owners

1. RTSP URL

The RTSP URL is the address that defines where the stream is coming from. It looks something like this:

rtsp://[username]:[password]@[IP address]:[port]/[path]

Components:

• Username/Password: If the stream is protected.
• IP Address: The server or camera’s address.
• Port: Default is 554, but it can be different based on the setup.
• Path: Location or name of the media stream (e.g., live.sdp).

2. Network Bandwidth

• Bandwidth Requirements: RTSP streaming, especially in high-definition (HD), will need sufficient bandwidth so that your videos will be smooth when the viewers watch it. 
• The stream will demand for more bandwidth if the resolution and frame rate have to be high enough for a decent stream. 
• Common Bandwidth Recommendations:
  • SD (480p): 1-2 Mbps
  • HD (720p): 3-5 Mbps
  • Full HD (1080p): 5-10 Mbps
  • 4K: 15-25 Mbps

3. Protocols Working with RTSP

• RTP (Real-Time Transport Protocol): Handles the actual data transfer of video and audio packets of your stream from the server to the client
• RTCP (Real-Time Control Protocol): Provides feedback on the quality of the stream (packet loss, jitter, etc.) and makes sure that the RTP session runs smoothly.
• TCP/UDP: RTSP can run over TCP (reliable, ordered transmission) or UDP (faster, but more prone to packet loss). It is very important to understand the difference between the two. So that you’ll know when to use TCP (for reliable delivery) and when to use UDP (for low latency).

4. Latency Considerations

• Low Latency: When it comes to live streaming or real-time communication, everyone aims for the lowest latency to satisfy users with a super-smooth streaming experience. You might have to prioritize maintaining low latency at all phases of the streaming process. 
• Where should you be careful with latency:
  • Network speed and stability
  • Codec processing time
  • Buffering settings in the streaming software/hardware

5. Codec Compatibility

• RTSP supports various video and audio codecs, but the most common codecs used in streaming are:
  • Video: H.264, H.265 (HEVC)
  • Audio: AAC, G.711, G.726
• Codecs determine the compression quality of the stream. If you compress your stream more, you will save bandwidth, but it might reduce the video quality. So, you just need to be a bit cautious about choosing the codecs, considering the quality. 

7. Playback Devices and Software

• Compatible Media Players: You can play an RTSP stream on various media players like VLC, QuickTime, and RealPlayer.
• IP Cameras and Streaming Devices: Many IP cameras support RTSP, allowing direct live streaming from the camera.
• Streaming Software: OBS (Open Broadcaster Software) or other software can capture RTSP streams for broadcast.

Choose any device or software, but make sure they are compatible and do not affect the streaming experience for your users. 

8. Error Handling and Debugging

There are times your streaming app might pop up error messages. 

• Common Errors:
  • 404 Not Found: Stream path or URL is incorrect.
  • 403 Forbidden: Access to the stream is restricted, possibly due to authentication.
  • 500 Internal Server Error: Server-side issue.
• What debugging tools can you use?
  • Use network monitoring tools like Wireshark to analyze RTSP traffic.
  • VLC Player offers detailed logs for debugging RTSP streams.

9. Authentication and Security

• Some RTSP streams require authentication (username and password) to access them. This is very important if you are publishing a private stream. 
• Encryption: RTSP is typically unencrypted, but it can be used with SRTP (Secure RTP) for secure media delivery.

10. Stream Scalability

• RTSP is primarily a one-to-one protocol where a client connects directly to a server.If you think you need to scale your stream to many viewers, you can consider using a streaming server (like Wowza or Red5) or CDN (Content Delivery Network) that can redistribute the RTSP feed to multiple viewers.

11. Redundancy and Backup Streams

• It is always safe to have backup streams or redundancy with you, in case the primary RTSP feed fails. This can be done by setting up multiple RTSP servers or using failover mechanisms.

12. Cross-Device Compatibility

• You can stream the media on Windows, macOS, iOS, Android, Linux or any platform you prefer. Just that you need to understand that the implementation may vary across devices.
• It is better to do cross-device testing to make sure that your streams are playable across devices. 

13. Recording RTSP Streams

• Your viewers can record a gameplay stream or live event and watch it later. This is possible because RTSP supports the Record option. 
• Many NVRs (Network Video Recorders) and software like VLC support recording RTSP streams.

What Next?

You now know how important the RTSP protocol is when developing a live streaming app. 

But is there an easier way to do it?

Yes! 

ApphiTect is a fully customizable live streaming solution that’s built with all the core live streaming protocols that’s necessary to keep your streams smooth and lag-free to watch. 

The best part is, you can tell the team your requirements and they’ll deliver a uniquely customized solution for your live streaming platform. 

Sounds interesting?

Wait no more! Get on a call with our team and they’ll take care of the rest. 

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Further Reading

• Top 10 White Label Live Streaming SDK & API Providers
• How to Create a Live Streaming App? – Types, Features, Cost