We have many such live broadcasts, but the performance place is far from the computer room, but we can all see each other, that is, there is no distance in a straight line.
Today, I bought a TP-LINK 64 1G wireless router and a wireless network card for the experiment. I just got back, not bad, but I don't know how long it has been. I want to use omni-directional antenna on the roof of the computer room and directional antenna in the performance area. How to choose an antenna? What if the video transmitted by the streaming media server is unclear?
System requirement analysis
We can see that this network broadcasting system consists of two parts: one is the wireless point-to-point bridging network system; Second, the signal processing system.
Point-to-point wireless bridge system, we have introduced many cases. In this case, due to the linear distance of nearly 3KM, it can only be realized by a professional wireless bridge. The so-called professional wireless bridge is composed of carrier-grade wireless bridge, high-gain antenna system and accessories. Wireless routers generally do not have the function of bridging (of course, there are some working modes of bridging, but the distance is not that far), so it is definitely difficult to assume this responsibility. In addition, in this case, the distance between the two points is still far, and it is better to use a directional antenna.
The signal processing system includes the "program source acquisition and coding" part of the entertainment scene and the "media server playing" part of the back-end TV room. In the coding part of program source acquisition, the camera shoots the original video, synchronously records the audio to obtain analog signals, which are input into the computer through the video acquisition card and sound card of the computer respectively, and then encoded in the computer by the encoder to form digital signals, which are transmitted to the back-end media server through the network, and the media server outputs the analog signals to enter the cable TV network.
Program description
As we already know, this live broadcast system consists of two systems, which are described in detail below:
First, the realization of wireless point-to-point bridging network system
The following figure is the network topology diagram of this wireless point-to-point bridging network:
Network topology diagram of wireless point-to-point bridging network
We can see that at the performance site, audio and video digital signals in coded format are transmitted back to the computer room through a wireless bridge and a grid parabolic directional antenna. Of course, the wireless access of the computer room is also composed of a set of point-to-point wireless bridges and grid parabolic directional antennas. If this unit is based on standardized network design, it should adopt integrated wiring system, and the computer room is the core of the three networks.
Therefore, after the wireless bridge in the computer room accesses the signal, it first accesses the switch, then it is processed by the media service of the same access switch, and then it is "broadcast" to the broadband network (local area network) so that all computers in the local area network can see the program. Of course, the requirement of this case is to broadcast through cable TV network, so the media server is required to have direct output of analog signals and connect to the control platform of cable TV network. The analog signal output here can be realized by a graphics card with S terminal.
Here we should pay attention to the following issues:
1, the wireless bridge and the grid parabolic directional antenna must be based on the same wireless standard (such as 802. 1 1b or 802. 1 1g), the same radio frequency mode (such as direct sequence spread spectrum (DSSS)), and the same wireless output power.
2. Directional antennas should also be based on the same wireless standard and have the same gain value, which is the best.
3. Because it is microwave transmission, the signal propagates almost in a straight line, so the antenna should be visible in a straight line of sight, and the antenna should generally be placed on a tall building.
Second, the realization of the signal processing system The following figure is the flow chart of the signal processing system:
Flow chart of signal processing system
In this picture, it shows that we will use Microsoft's three technologies-"Three donkey kong" as the program signal processing, and finally access the cable TV network through the local area network. These three donkey kong are: Windows Encoder 9 encoder used on the front-end coding workstation; Windows Media Service 9 Media Server used on the back-end server and Windows Media Player 9 media player used on the back-end server.
Windows Media 9 encoder is a production tool for converting real-time and pre-recorded audio and video into "Windows Media files" or "streams". By compressing audio and video content, you can broadcast content with the help of Internet bandwidth. This software can be downloaded and installed on Microsoft's website.
Windows Media Services 9 is a platform for transmitting audio and video content to clients through Internet or Intranet. These clients can be other computers that use a player (such as Windows Media Player) to play content (in this case, we play it directly on the server), or other Windows Media Services computers that are used to proxy, cache or redistribute content.
The content transmitted by the Windows Media server to the client can be a real-time stream or a pre-existing digital media file. In this case, the real-time streaming content from Windows Media encoder will be transmitted. Windows Media Services 9 series is a component of Windows Server 2003 server operating system, which needs to be installed selectively. Windows Media Player 9 Media Player needs no introduction, as everyone knows.
In addition, the coding workstation should be equipped with a "video acquisition card" to receive the video signal of the camera and a "sound card" to receive the audio signal of the mixer.
The final realization process of the program signal processing system is as follows:
The 1. coding workstation collects video and audio signals respectively through a video acquisition card and a sound card, and then encodes them with a Windows Encoder 9 encoder on the local computer to generate a "stream" with Microsoft's unique format, which can be transmitted on the network, such as http:/10.1.3: 9000.
2. The 2.Windows Media Services 9 server receives the "stream" from the encoder and forms a broadcast address (for example: MMS:/10.10.1.5/TV, where TV is the name of the publishing point), and then computers on the network can access this address to receive and play the program stream.
3. Enter the "publishing point" address of the above media server program in the "Open URL" on the Windows Media Player 9 media player (as above: MMS:/10.10.5/TV) to play the program on the player. One thing to note here is that the player can actually directly access the address of the encoder (as above: http:/10.10.1.3: 9000) to directly play the program, but this will make the encoding workstation paralyzed in the case of a large number of requests, because it has no service function and no cache concurrency and other operations.