Shulou(Shulou.com)06/02 Report--

Live broadcast has directly evolved our way of communication from the traditional two-dimensional space to the current three-dimensional mode, the main reason is that live broadcast has a strong real-time and interactive function. In the computer network, the exchange of information must be carried out in accordance with the agreed process in advance in order to realize the interaction between entities, which is the transmission protocol in the network. If there is no transmission protocol, there will be problems in the exchange of information between the two parties. So today, let's talk about some network transmission protocols that can be used in the process of building a live broadcast system.

1. RTMP protocol:

RTMP is the abbreviation of Real Time Messaging Protocol, that is, the real-time message transmission protocol. RTMP is a network protocol designed for real-time data communication. It is an open protocol developed by Adobe Systems for audio, video and data transmission between Flash players and servers. Because the general audio and video formats are flv and f4v. Web is played by flash player, which is basically supported by most browsers on PC, but hardly supported by mobile. It is mainly used for audio, video and data communication between Flash/AIR platform and streaming media / interactive server supporting RTMP protocol.

It has many variants:

1) RTMP works on TCP. Port 1935 is used by default.

2) RTMPE adds encryption function to RTMP.

3) RTMPT is encapsulated on the HTTP request and can penetrate the firewall

4) RTMPS is similar to RTMPT, adding the security function of TLS/SSL.

2. RTSP protocol:

RTSP (Real Time Streaming Protocol), that is, real-time streaming protocol. RTSP defines how one-to-many applications effectively transmit multimedia data over IP networks and provides an extensible framework where data sources can include real-time data and existing stored data. The protocol is used to control the connection of multiple audio or video data, and the server can choose to use TCP or UDP to transmit streaming content. Because RTSP does not put special emphasis on time synchronization, there may be network delay, but RTSP has a redirection function and can switch servers that provide services according to the actual load, so the delay caused by excessive server load can be avoided to some extent.

3.RTP protocol:

RTP (Real-time Transport Protocol), which is the real-time transport protocol. End-to-end transmission services with real-time characteristics are provided for data, such as interactive video, audio or analog data under multicast or unicast network services. RTP protocol transmits data based on UDP protocol by default, and low latency can reach the level of milliseconds. Although the RTP protocol does not prevent unordered transmission and is not sure of the reliability of the underlying network, it is sent regardless of whether the transmission is lost or not, regardless of whether the receiver has received the packet or not, but RTP implements orderly transmission, and the sequence number in RTP allows the receiver to reorganize the sender's packet sequence, and the sequence number can also be used to determine the appropriate packet location, such as in video decoding, there is no need for sequential decoding. Based on these features of the RTP protocol, RTP is widely used in streaming media-related communications and entertainment, including telephone, video conferencing, television and web-based push-to-talk services (similar to walkie-talkies).

4. RTCP protocol:

RTCP is RTP Control Protocol (RTCP: RTP Control Protocol). The main function of RTCP is to provide feedback on the quality of service provided by RTP and collect statistical information about media connections. For example, the number of transmission bytes, the number of transmission packets, the number of lost packets, one-way and two-way network delay and so on. Network applications can use the information provided by RTCP to improve the quality of service, such as limiting traffic or switching to codecs with low compression ratio. Therefore, RTCP is the supporting protocol of RTP, which cooperates with RTP to package and send multimedia packets, and regularly transmits control data between participants in multimedia stream sessions.

5. HTTP-FLV protocol

HTTP is a simple request-response protocol that usually runs on top of TCP. It specifies what kind of message the client might send to the server and what kind of response it gets. Flv is an audio and video encapsulation format, the full name is Flash Video, is a streaming media format, can be played through the flash player. FLV protocol, mainly promoted by Adobe, is extremely simple in format. It only adds some tag header information to large video frames and audio and video headers, and is very mature in terms of delay performance and large-scale concurrency. However, the support on mobile browsers is very limited, but it is very suitable to be used as a mobile APP live streaming protocol.

6.HLS protocol

The full name is HTTP Live Streaming, HLS protocol is the streaming media playback protocol proposed by Apple. The video is divided into small video fragments of 5-10 seconds, and then managed with the m3u8 index table. Because the videos downloaded by the client are complete data of 5-10 seconds, the fluency of the video is very good, but it also introduces a large delay (the general delay of HLS is about 10-30 seconds). Compared to FLV,HLS 's support on iPhone and most android mobile browsers, it is very powerful. HLS protocol client support is simple, only need to support HTTP requests, HTTP protocol is stateless, only need to download media fragments sequentially, and network compatibility is good, HTTP packets can easily pass through the firewall or proxy server. However, compared with persistent connection protocols such as RTMP, the latency of ILVB scenarios is higher.

These are our common network transport protocols. Generally, RTMP protocol and HLS protocol are widely used in the construction of live broadcast system, and the live broadcast system can run smoothly based on these protocols.

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