Two mainstream stream transmission types and the characteristics of Stream Transmission

Source: Internet
Author: User
Tags dedicated server

Streaming Transmission is widely defined. It is a general term for the technology that transfers media (such as videos and audios) over the network. Its specific meaning is to transmit video programs to PCs over the Internet. There are two methods to implement stream transmission: realtime streaming and progressive streaming ). (Baidu encyclopedia)

Currently, audio/video (A/V) and other multimedia information are transmitted over the network in two ways: Download and stream transmission. A/V files are generally large, so they require a large storage capacity. At the same time, due to network bandwidth restrictions, downloading often takes several minutes or even hours, therefore, this processing method has a high latency. During stream transmission, the base media is continuously transmitted to the user's computer in real time, such as audio, video, or animation. You do not have to wait until the entire file is downloaded, however, you only need to watch the video after several or dozens of seconds of startup latency. When the base media plays audio on the client, the remaining part of the file will be downloaded from the server in the background. Streaming not only shortens the startup Latency by 10 times and a hundred times, but also does not require a large cache capacity. Streaming Transmission prevents users from waiting for the entire file to be downloaded from the Internet for viewing.

  1. Types of Stream Transmission

Network Transmission of audio, video, and other multimedia information can be downloaded or streamed. The download scheme requires a large storage capacity due to the large size of A/V files, in addition, the network bandwidth limit leads to a long download time and a large delay. However, the stream transmission solution avoids the disadvantage that users can play the video only after the entire file is downloaded. Stream Transmission is divided into two types: Sequential stream transmission and real-time stream transmission.

① Progressive streaming)

Ordered stream transmission downloads objects sequentially. You can watch online programs while downloading objects. At a given time point, the user can only view the downloaded part, but cannot jump to the part that has not been downloaded. Unlike real-time stream transmission, Sequential stream transmission can be adjusted based on the speed of user connection during transmission. Because the standard HTTP server can send files in this form without other special protocols, it is often called HTTP stream transmission. Because the part of the file to be viewed before playback is lossless and the final playback quality is good, it is particularly suitable for short clips with high quality, small data volume, and released through Modem, such as titles, credits, and advertisements. However, users must experience several seconds of delay before watching, especially when the transmission speed is slow. For short clips published through the modem, Sequential stream transmission is very useful, and it allows you to create video clips at a higher data rate than the modem. Despite latency, high-quality video clips can be released. Ordered streaming files are stored on standard HTTP or FTP servers, which are easy to manage and are basically irrelevant to firewalls. Ordered stream transmission does not support long clips and videos with random access requirements, such as lectures, presentations, and Demos. It also does not support on-site broadcast. Therefore, strictly speaking, it is essentially a VOD technology.

② Realtime Streaming)

Real-time stream transmission ensures that the media signal bandwidth matches the network connection and allows you to watch programs in real time. Unlike HTTP streaming, Real-Time Streaming requires a dedicated Streaming Media Server and transmission protocol. Real-time stream transmission is always transmitted in real time, so it is especially suitable for on-site events and supports random access. Users can fast forward or backward the content to view the content before or after. Theoretically, a real-time stream cannot be stopped once it is played, but in fact it may be paused periodically. Real-time stream transmission must match the connection bandwidth, which means that the image quality is poor when connected at the modem speed. In addition, due to errors and loss of information, the quality of the video is poor when the network is busy or a problem occurs, but the quality of the video is good without Sequential stream transmission. Real-time stream transmission requires specific servers, such as QuickTime
Streaming Server, RealServer, and Windows Media Server. These servers allow you to have more levels of control over media sending, making system settings and management more complex than standard HTTP servers. Real-Time Streaming also requires special network protocols, such as RTSP (Realtime Streaming Protocol) or MMS (Microsoft Media Server ). These protocols sometimes have problems when there is a firewall, so that users cannot see the real-time content of some locations.

Obviously, in actual use, the specific transmission mode can be determined as needed, and streaming transmission also supports full download to the hard disk before playback. Generally, the stream transmission mode uses the RTP/UDP and RTSP/TCP communication protocols to establish A connection with the/V (Audio/Video) Server, redirects the server output to A running A/V
The destination address of the client where the Player program is located. Generally, a dedicated server and player must be configured for a stream transmission system.

  2. Stream Transmission features

Compared with the pure download mode, this stream transmission mode for simultaneous download and playback of multimedia files has the following features:

① Greatly shorten the startup latency

Streaming Transmission greatly reduces the startup latency because users do not have to wait for all the content to be downloaded to the hard disk before browsing. Both the working hours and evening are fast. Generally, a 45-minute video clip is displayed on the client within one minute, and does not appear intermittently during playback. In addition, full-screen playback has almost no effect on the playback speed, but it takes time to wait for fast forward and reverse playback.

② Greatly reduce the demand for system cache capacity

Because the Internet implements intermittent asynchronous transmission based on packet transmission, its data is divided into many packets for transmission. The dynamically changing network makes it possible to select different routes for each package, so the delay in reaching the user's computer is also different. Therefore, the client needs a cache system to compensate for the delay and jitter effects and ensure that the packet transmission order is correct, so that the media data can be continuously output, it does not pause playback due to temporary network congestion. Streaming Transmission still needs to be cached, but because it does not need to download all the animation and audio content to the cache, the cache requirements are greatly reduced.

Because the streaming media technology uses the data buffer technology, it can keep streaming media uninterrupted and ensure the reliability of file transmission.

③ Specific real-time transmission protocols are available for stream transmission

As mentioned above, streaming media currently has three mainstream formats and requires specific real-time transmission protocols. Generally, RTSP and other real-time transmission protocols are used for real-time stream transmission of animation and video and audio on the Internet.

In addition, the use of streaming media technology does not occupy local hard disk space.

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