Streaming media report 1.1 Overview The so-called streaming media refers to the media formats transmitted over the network through streaming, such as audio, video, or multimedia files. Streaming media does not download the entire file before playback. It only saves some of the initial content to the memory, caches data packets on the computer, and outputs the media data correctly. Streaming media data streams can be transmitted at any time, but some latency occurs at the beginning. Obviously, the key technology for implementing streaming media is stream transmission. Streaming Transmission mainly refers to parsing the entire audio, video, three-dimensional media, and other multimedia files into compressed packages through specific compression methods, the video server sends messages to users in sequence or in real time. In a system that uses stream transmission mode, you do not have to wait until the entire file is downloaded, as in the case of downloading, however, after several or dozens of seconds of startup latency, you can use the unzipping device to decompress the compressed multimedia file and play and watch it. The remaining part of the multimedia file will be downloaded from the backend server. This technology first creates a buffer on the computer, and downloads a piece of data before playing as a buffer. When the actual speed of the network connection is less than the speed of the Data consumed by playing, the playing program will use the data in this short buffer to avoid playing interruption and maintain the playing quality. 1.2 streaming media file format 1.2.1 Ra's audio format and RM video image format Ra format are a new stream audio real audio file format developed by Real Networks. The RM format is the real video file format of streaming videos. It is mainly used to transmit active video images in real time on low-rate networks. Different compression ratios can be used based on different network data transmission rates, during the data transmission process, you can download and play the video and image to transfer and play the image data in real time. The client can play the video through the Real Player player. 1.2.2 ASF of Microsoft Media Technology is also a popular online streaming media format. Its use is inseparable from the Windows operating system. Its player Microsoft Media Player is already bundled with windows, not only used for Web playback, it can also be used to play audio and video files outside the browser. 1.2.3 The H.263 format is also one of the 3GPP specifications. The extension is Avi and features include: 1. Suggestions on Narrowband Channel Video Encoding with a bit rate lower than 64 kbit/s. 2. developed on the basis of H.261's recommendation, its frequency is more than 10 Gb/s per second. the image resolution is 175x144 pixel (qcif), or 128x96 pixel (sub-qcif) 1.2.4nancy format only loads less than 1/10 of Mpeg-4 mode using decimal discrete cosine transform (DCT), motion estimate, Huffman, and run length. Nancy codec only requires four types of operations, comparison and bit-shift ). Instead of using DCT, me, and run length, you can provide video content services before 3G services, such as video emails and video downloads. Feature 1. real-time software coding 2. the most lightweight encoding/decoder, low power consumption, high fault tolerance 3. very high price ratio, low-cost basic investment, but Nancy is not a 3GPP solution. 1.2.5 comparing the advantages and disadvantages of media types 3GPP standard recommendation RM mature standard compression algorithm complexity is recommended to use MPEG-4 mature standard compression algorithm complexity is recommended to use H.263 mature standard compression algorithm complexity is recommended to use Nancy compression algorithm is simple it is not recommended to use the 1.3 Streaming Media Technology for non-standard purposes, the most popular streaming media formats include real System of Real Networks, Windows Media Technology of Microsoft, and QuickTime of Apple. These are the three major online streaming media transmission systems. 1.3.1 real system consists of three parts: media content production tool real producer, server Real Server, and client software. Its streaming media files include RealAudio, real video, real presentation, and real Flash files, which are used to transmit different files respectively. Real system uses the sure stream technology to automatically and continuously adjust the traffic of data streams to adapt to various network bandwidth requirements in actual applications, and easily implement video/audio and 3D animation playback on the Internet. 1.3.2 Windows Media Technology is a stream-based playback solution proposed by Microsoft. It is designed to transmit multimedia stream information including audio and video information over the Internet and the Internet. Its core is the ASF (Advanced stream format) file. ASF is a data format that includes audio, video, image, control command, script, and other multimedia information, stream multimedia content is published by dividing network data packets into different types and transmitting them over the Internet. Therefore, the content transmitted over the network is called ASF stream. ASF supports arbitrary compression/Decompression encoding methods, and can use any underlying network transmission protocol, with great flexibility. Microsoft has bound Windows Media Technology to Windows 2000 and intends to use ASF as the standard file format for multimedia content in future Windows versions, this will undoubtedly have a significant impact on the application and development of Internet, especially stream technology. Windows Media Technology consists of media tools, Media Server, and media player. Media tools is an important part of the entire solution. It provides a series of tools to help users generate asfformat Multimedia Streams (including real-time generated Multimedia Streams ), these tools can be divided into creation tools and editing tools. creation tools are mainly used to generate Multimedia Streams in asfformat. editing tools are mainly used to edit and manage multimedia stream information in asfformat, this includes post-production editing tools and ASF check that checks the ASF stream and corrects errors. Media Server ensures the confidentiality of files and prevents them from being downloaded. It allows each user to browse the webpage with the best video quality. It has multiple file publishing forms and monitoring and management functions. Media Player provides powerful stream information playing functions. 1.3.3 QuickTime Apple launched QuickTime in 1991. It supports almost all mainstream personal computing platforms and static image files, videos, and animation formats in various formats, with the built-in Web browser plug-in technology, it supports IETF (Internet Engineering Task Force) Stream standards and network protocols such as RTP, RTSP, SDP, FTP, and HTTP. QuickTime includes the server Quicktime Streaming Server, the player QuickTime player with editing functions (free of charge), the production tool QuickTime 4 pro, the image browser picture viewer, And the QuickTime plug-in that enables the Internet browser to play QuickTime movies. QuickTime 4 supports two types of stream: Real-time stream and Quick Start stream. A QuickTime video that uses real-time streams must be played from a server that supports QuickTime streams. It is a streaming media in the true sense and uses the real-time transmission protocol (RTP) to transmit data. A Quick Start video can be played from any web server and transmitted using Hypertext Transfer Protocol (HTTP) or file transfer protocol (FTP. 1.4 stream media transmission 1.4.1 pre-processing multimedia data must be pre-processed to be suitable for stream transmission. This is because the current network bandwidth is far from enough for massive multimedia data traffic. Preprocessing uses advanced and efficient compression algorithms to compress multimedia information. The compressed encoding data can be transmitted in multiple ways using text, graphics, and scripts, and stored in a file structure that can implement stream, this means that the file has the time mark and other features that are easy to implement stream, and then decode the file on the client. The encoding process is an art. We should consider the customization performance of different encoding speeds, packet loss fault tolerance, and network bandwidth fluctuations, playing effect, encoding/Stream Transfer cost, stream control, and other aspects at the lowest speed. 1.4.2 cache stream transmission needs to be cached. This is because the Internet implements intermittent asynchronous transmission based on packet transmission. During transmission of a real-time multimedia file, they will be divided into many packets, because the network is dynamic, the routes selected by each package may be different, so the delay in arriving at the client may not be the same, or even the first packet may arrive later. Therefore, the cache system is used to compensate for the impact of latency and jitter, and ensure that the data packets are in the correct order, so that the media data can be continuously output without pausing the video due to temporary network congestion. The cache usually requires a small amount of capacity, because the cache uses a circular linked list structure to store data: By discarding the played content, "stream" can reuse the empty cache space to cache the content that has not been played. 1.4.3 after selecting a first-class media service during transmission, the web browser and the Web server exchange control information over HTTP/tcp to retrieve the real-time data to be transmitted from the original information; then, the Web browser on the client starts the client program and uses http to retrieve relevant parameters from the Web server to initialize the client program. These parameters may include directory information, data encoding type, and retrieval-related server addresses. The customer program and server run the real-time traffic control protocol (RTSP) to exchange the control information required for transmission. Similar to functions provided by CD players or VCRs, RTSP provides methods to manipulate commands such as playback, fast forward, fast backward, pause, and recording. The server uses the RTP/UDP protocol to transmit data to the client program. Once the data arrives at the client, the client program can play the output. 1.5 The stream transmission protocol has a specific real-time transmission protocol, including the multimedia transmission protocol of the Internet and some real-time stream transmission protocols, only when appropriate protocols are used can streaming media play a better role and ensure the transmission quality. IETF (Internet Engineering Task Group, the main Organization for Standardization of Internet Planning and Development) has designed several protocols that support streaming media transmission. It is mainly used for real-time transmission protocol RTP (Real-Time Transport Protocol) for multimedia data streams over the Internet) real-time transmission control protocol RTCP (Real-Time Transport Control Protocol) that provides traffic control and congestion control services with RTP) defines the Real-Time Streaming Protocol RTSP (Real-Time Streaming Protocol) for one-to-multiple applications to effectively transmit multimedia data over an IP network ). 1.5.1 real-time transmission protocol RTP (Real-Time Transport Protocol) is a transmission protocol for multimedia data streams on the Internet. RTP is defined to work during one-to-one or one-to-many transmission. It aims to provide time information and implement stream synchronization. RTP usually uses UDP to transmit data, but RTP can also work on other protocols such as TCP or ATM. When an application starts a RTP session, two ports are used: one for RTP and the other for RTCP. RTP itself does not provide a reliable transmission mechanism for data packets transmitted in order, nor does it provide traffic control or congestion control. It relies on RTCP to provide these services. Generally, the RTP algorithm is not implemented as an independent network layer, but as part of the application code. 1.5.2 real-time transmission control protocol RTCP (Real-Time Transport Control Protocol) and RTP provide traffic control and congestion control services. During the RTP session, each participant periodically transmits the RTCP package. The RTCP package contains statistics such as the number of sent data packets and the number of lost data packets. Therefore, the server can use this information to dynamically change the transmission rate or even the payload type. RTP and RTCP can be used together to optimize transmission efficiency with effective feedback and minimal overhead. Therefore, RTP is particularly suitable for transmitting real-time online data. 1.5.3 real-time stream protocol RTSP (Real Time Streaming Protocol) is jointly proposed by Real Networks and Netscape, this Protocol defines how one-to-multiple applications can effectively transmit multimedia data over an IP network. RTSP is located on RTP and RTCP in the architecture. It uses TCP or RTP for data transmission. Compared with RTSP, HTTP transmits HTML, while RTP transmits multimedia data. HTTP requests are sent by the client and the server responds. When RTSP is used, both the client and server can send requests, that is, RTSP can be bidirectional. 1.5.4 Resource Reservation Protocol (RSVP) is a Resource Reservation Protocol under development on the Internet. Using RSVP can provide QoS for streaming media transmission to a certain extent.
