Using streaming media technology to network video, audio propagation of: Zhang Cheng Published: 2000/12/05
Thesis:
This paper summarizes the definition, principles, and development status of streaming media technology. On the basis of RealMedia as an application instance, the spread of streaming media technology implements audio, video information is spread on the network. Key words streaming media, realmedia, video, audio, internet
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The streaming technology is used to realize the video in the network, audio propagation, preface today, we are in a multicolored era of online. Quick links and multimedia computers have made messages on the network no longer just text, images, and simple sound files. More and more companies and individuals are using audio, video clip multimedia technology to make their own sites more attractive, with greater information quantity and economic benefits. These multimedia contents include movies, news editing radio, television broadcasts, online games, and even virtual pets. To use these multimedia information, you must implement the video, the transmission of audio information on the network. Second, what is a streaming stream is used to describe the name of the media file. Unlike routine files, media files can start playing during transmission to player. Why is this important? The reason is time. Media files usually have a huge size, and it takes a long time to download. Even short-to-30 seconds of video clips in normal per second 56kbps Internet access, 20 minutes or more download time. The 30-minute video file takes a few hours of download time. Since the data transmission process starts playing almost immediately, the download time problem is solved. Due to the "streaming" technology, the file is like water flow. The file is not a reading sent all the data, but first sends an audio or video clip in the line. While starting playback at the first part, the rest of the data is continuously flowing, and the destination is reached in time. To ensure that the playback does not interrupts in the case where the network speed is lowered, the player will collect a small number of so-called buffering preparation data before starting playback. If the data flow speed is fast enough, playback is continuous. Whether the file is 30 seconds or 30 minutes, the user is just a few seconds before waiting for a few seconds to make this buffer data. In general, streaming means a continuous time base medium using streaming technology on Internet / Intranet. Third, streaming medium technology 1. Realization of streaming transmission, first, multimedia data is pre-depleted to suit streaming, because the current network bandwidth is still not enough for multimedia huge data traffic. Pretreatment mainly includes two aspects: one is to reduce the quality; Second, adopting advanced and efficient compression algorithms. Second, the implementation of streaming needs to be cached. This is because the Internet is continuously transmitted by the Internet, for a real-time A / V source or stored A / V file, they are decomposed into many packets in transmission, because the network is dynamically changed, each The route selected by the package may not be the same, so the time delay that arrives at the client is not equal, and even the first packet is possible. To this end, the cache system is used to compensate for the influence of delay and jitter, and ensure that the order of the packet is correct, so that the media data can be continuously output, and the playback will be paused because the network is temporarily blocked. Usually the required capacity required in the cache is not large. This is because the cache uses a loop table structure to store data: "Flow" can be reused by discarding content, "stream" can reuse the empty cache space to cache content that has not yet played. Again, implementation of streaming requires a suitable transfer protocol. WWW technology is based on HTTP protocol, and HTTP is based on TCP protocols. Since TCP requires more overhead, it is not suitable for transmitting real-time data. In implementation of streaming, HTTP / TCP generally employs control information, and RTP / UDP is used to transmit real-time sound data. The process of streaming is usually as follows: (1) After the user selects a certain stream of media services, the web browser and the web server use HTTP / TCP exchange control information to retrieve the real-time data required to be transmitted from the original information; Then the web browser on the client starts the A / V Helper program, and the HTTP retrieves the relevant parameters to the Helper program initialized from the web server. These differences may include directory information, encoding types of A / V data or server addresses related to A / V retrieval.
(2), the A / V Helper program and the A / V server run the real-time flow control protocol (RTSP) to exchange the control information required for A / V transmission. RTSP provides methods for manipulating commands, fast forward, fast, pause, and recording. (3), the A / V server uses the RTP / UDP protocol to transfer A / V data to the A / V client, once the A / V data arrives at the client, the A / V client can play the output. In streaming, two different communication protocols with RTP / UDP and RTSP / TCP are connected to the A / V server, and is to be able to redirect the server to a client that is different from the run A / V helper program. The destination address. 2 Support streaming network protocol (1), real-time transfer protocol RTP (Real-TimeTransportProtocol), a transfer protocol for multimedia data streams on the Internet. RTP is defined as working in a one-to-one or more transmission, and the origin is to provide time information and realization flow synchronization. (2) Real-time transmission control protocol RTCP (Real-TimeTransportControlProtocol), and RTP provides traffic control and congestion control services. RTP and RTCP can be used in conjunction with efficient feedback and minimal overhead to optimize the transmission efficiency, thus particularly suitable for real-time data on the network. (3) Real Time Flow Protocol RTSP (RealTimeStreamingProtocol) defines how a pair of multimedia data is transmitted efficiently through IP networks. (4) RSVP protocol (ResourceRereveProtocol), the resource reservation protocol on the Internet is developed. 3, Identify streaming media types - Mime Mime is a thumbnue of MultiPurpose Internet Mail Extensions (General Internet Mail Extensions), which is not only for email, but also to mark any file types transmitted on the Internet. Through it, the web server and web browser can recognize streaming and perform corresponding processing. Both the web server and web browsers are based on the HTTP protocol, while HTTP has MIME. HTTP is using a wide variety of multimedia file formats on the MIME. In order to process a specific file format. MIME type settings are required for web servers and web browsers. For standard MIME types, such as text and JPEG images, the web server browser provides built-in support; however, for non-standard streaming file formats such as REAL, you need to set MIME types such as AUDIO / X-PN-ReaRaudio. 4. The browser conveys the streaming media support browser to identify the type of streaming, and call the corresponding program or plug-in to process, especially in IE, provide rich internal construction media support. Fourth, streaming media application and development Currently, more streaming video formats on the Internet mainly include the following: RealNetwork's RealMedia, Apple's QuickTime, and Microsoft's Advanced Streaming Format (ASF). Among them, RealNetwork's audio video compression specification RealMedia is currently a multimedia application standard for a fairly popular cross-platform client structure on the Internet, which uses audio video stream and synchronous playback techniques to provide full bandwidth on intranet. The highest quality multimedia can also provide stereo and continuous video on the Internet. Therefore, the case where the streaming medium application is explained below as an example of RealMedia.
