Using Streaming Media Technology for video and audio transmission on the network
Today, we are in an age of colorful and exquisite networks. Quick Links and the emergence of multimedia computers make the information on the network no longer just text, images and simple sound files. More and more companies and individuals are making use of the multimedia technology of audio and video editing to make their websites more attractive, have more information and economic benefits. These multimedia contents include movies, news editing stations, television broadcasting, online games, and even virtual pets. To use this multimedia information, you must transmit the video and audio information over the network.
2. What is streaming media?
Stream is a term used to describe media files. Unlike conventional files, media files can be played during transmission to the player. Why is stream so important? The reason is the time. Media files are usually bulky and it takes a long time to download them. It may take more than 20 minutes for a video clip to be transmitted over 56 kbps per second over the Internet. However, it takes several hours to download a 30-minute video file.
Since the data sending process starts playing almost immediately, the download time problem is solved. Thanks to the "stream transmission" technology, files flow like water streams. The file does not read and send all the data at a time, but first sends the first part of the audio or video clip in the line. When the first part starts playing the video, the rest of the data is continuously flowing out to reach the destination in time for playing. To ensure that the playback will not be interrupted when the network speed decreases due to blocking, the player collects a small portion of the so-called buffered preparation data before starting playing the video. If the data flow speed remains fast enough, the playback is continuous. Whether the file is 30 seconds or 30 minutes long, the user only generates this buffer data several seconds before watching the file.
In general, streaming media is a continuous, time-based media that uses Stream Transmission Technology on the Internet/Intranet.
Iii. Technical Principles of streaming media
1. Implementation and process of Stream Transmission
First, multimedia data pre-processing can be suitable for stream transmission, because the current network bandwidth is far from enough for the massive data traffic of multimedia. Preprocessing mainly includes two aspects: first, quality reduction; second, advanced and efficient compression algorithms.
Second, stream transmission needs to be cached. This is because the Internet implements continuous asynchronous transmission based on packet transmission. for a real-time A/V source or stored A/V file, they are divided into many packages during transmission, because the network changes dynamically, the routes selected for each packet 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 capacity is usually not large. This is because the high-speed cache uses the linked list structure to store data: By discarding the content that has been played, "stream" can reuse the empty high-speed cache space to cache the content that has not been played in the future.
Thirdly, the implementation of stream transmission requires a suitable transmission protocol. WWW technology is based on the HTTP protocol, while HTTP is based on the TCP protocol. Because TCP requires a lot of overhead, it is not suitable for transmitting real-time data. In the implementation scheme of stream transmission, HTTP/TCP is generally used to transmit control information, however, RTP/UDP is used to transmit real-time sound data.
The process of stream transmission is usually as follows:
(1) After selecting a first-class media service, the web browser and the Web server use HTTP/tcp to exchange control information so that the real-time data to be transmitted can be retrieved from the original information; then, the Web browser on the client starts the/V Helper Program and uses http to retrieve relevant parameters from the Web server to initialize the Helper Program. These differences may include the directory information, the encoding type of A/V data, or the server address related to A/V retrieval.
(2) A/V Helper Program and A/V server run the real-time traffic control protocol (RTSP) to exchange the control information required for A/V transmission. RTSP provides commands such as playing, fast forward, fast backward, pause, and recording.
(3) the/V server uses the RTP/UDP protocol to transmit a/V Data to A/vclient. Once A/V data arrives at the client, a/vclient program can play the output.
In stream transmission, two different communication protocols, RTP/udp and RTSP/tcp, are used to establish contact with A/V server, this is to redirect the server output to a destination address different from the client where the/V helper program is running.
2. network protocols supporting streaming media transmission
(1) real-time transmission protocol RTP (Real-timetransportprotocol) 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, with the aim of providing time information and implementing stream synchronization.
(2) real-time transmission control protocol RTCP (Real-timetransportcontrilprotocol) provides traffic control and congestion control services together with RTP. RTP and RTCP are used together to optimize transmission efficiency with effective feedback and minimal overhead. Therefore, RTP is particularly suitable for transmitting real-time online data.
(3) Real-time stream protocol RTSP (realtimestreamingprotocol) defines how one-to-multiple applications can effectively transmit multimedia data over an IP network.
(4) resourcereserveprotocol, a Resource Reservation Protocol under development on the Internet.
3. Identify the stream media type-mime
Mime is the abbreviation of Multipurpose Internet Mail Extensions (universal Internet Mail Extension). It is used not only for email, but also for marking any file type transmitted over the Internet. The Web server and Web browser can identify and process streaming media. Both the Web server and Web browser are based on the HTTP protocol, while both HTTP have mime content. HTTP marks a wide range of multimedia file formats on the Web through mime. To process a specific file format. You must set the MIME type for both the Web server and Web browser. The Web Server Browser provides built-in support for standard MIME types, such as text and JPEG images. However, for non-standard streaming media file formats such as real, set MIME types such as audio/X-PN-RealAudio.
4. browser support for streaming media
The browser uses mime to identify the streaming media type and calls the corresponding program or plug-in for processing. Especially in IE, it provides rich built-in streaming media support.
Iv. Streaming Media Application and Development
Currently, many streaming video formats are used on the Internet, including RealMedia of RealNetwork, QuickTime of apple, and Advanced Streaming Format (ASF) of Microsoft ).
Among them, RealMedia, the audio and video compression specification developed by RealNetwork, is a multimedia application standard for cross-platform client server structures that are currently quite popular on the Internet, it uses audio video streams and synchronous Playback Technology to implement full bandwidth on the Intranet to provide the best quality multimedia, while also providing stereo and continuous video on the Internet. Therefore, the following uses RealMedia as an example to describe the situation of streaming media applications.
1. creation process of streaming media
Streaming media can be divided into two types of content submission: Live streaming media broadcast (web broadcast) and archived video and audio accessed by users on demand. No matter which type of streaming media, the transformation from the original camera to the stream content must go through the following process:
(1) recording events;
(2) edit the content, and then use the video editing hardware and software to digitize it;
(3) digital video and audio content are encoded in streaming media (. Ram) format.
(4) media files or live data streams are stored on the host computer where the streaming media server software is installed;
(5) The user clicks the webpage to request a video stream or access the database of the stream content;
(6) The host server submits digital content to the end user, and the end user views the digital content using the playback program (RealPlayer) that displays the media content on the desktop.
Figure 1 shows the process of making streaming media in the RealMedia format of RealNetwork.
2. Create a. rm file on a computer
To convert a digital file to a. rm file, RealNetwork provides the background production software realproducer, which supports conversion of existing files and real-time live streaming. Here, you must correctly set the file storage path and select the appropriate file conversion grade. (Based on the network bandwidth, realproducer provides a variety of conversion formats for. rm files, which can be spread from 28.8k to 100m in different bandwidths.
3. install streaming media publishing software on the Web Server
RealNetwork provides RealServer as the release software for RealMedia files. Therefore, you must install the RealServer server program on the Web server and set it correctly.
(1) install the service program;
(2) set the MIME type
4. embed the RealPlayer player into the webpage
After installing and configuring the server and preparing the. rmwenjian, you can use the. rm file on the web page. Two commonly used forms are:
(1) Use standard HTML to connect to the. rm file.
(2) Use <embed> to mark real-time embedded. rm files
5. Install the RealPlayer player for the client
V. The future of streaming media
Streaming media service systems are different from network file service systems. From the perspective of function implementation, although the streaming media network service system and the traditional network file service system have many similarities, especially the sharing and use of data objects and the pursuit of maximum data throughput, streaming media emphasizes support for high-speed, stable, and continuous access streams, and synchronization to ensure that media data arrives on time.
With the development of computer networks and the constant expansion of network bandwidth, especially the advent of internet2, streaming media technology will certainly play a greater role in the future network applications.