In the field of video conference, there are many open source projects that can be referred to. Some of these open-source projects are protocol stack, encoder or transmission protocol. Because video conference system is a comprehensive application system, it contains many functions. For example, these open source projects can be selectively added to our video conference development, Our development efficiency will certainly be twice as high as half the effort. Let's list the top ten open source projects related to video conference, and make a comprehensive evaluation and ranking of its importance, advantages and disadvantages.
1. OpenH323 project
Reasons for listing: the most famous open source H.323 protocol stack, the necessary protocol stack for video conference development, highly recommended
The most famous H.323 open source protocol stack contains all the H.323 protocol functions, and has a large number of reference examples for video conference implementation, such as terminal, MCU server, GK and other core components of H.323 protocol. OpenH323 is the first protocol stack of H.323 protocol, and it is also one of the most valuable open source projects for our video conference development.
Download address: http://www.h323plus.org/source/
2. Ffmpeg project
Reasons for listing: the most comprehensive open source encoder, including H.264, MPEG4, g.72x, etc., is also highly efficient, and it is highly recommended
At present, the most comprehensive open source encoder, including the commonly used audio and video coding protocols H.264, MPEG4, H.263, g.721, G.726, G.729, etc. Although ffmpeg is an open source project based on Linux, it can be run under windows by cross compilation. Many optimized efficiency codes are added to the project, such as assembly instead of C, greatly improving the coding efficiency, Ffmpeg is recommended for real-time coding of video conferencing.
Download address: http://ffmpeg.org/download.html
3. Webrtc project
Reasons for listing: Google has purchased open source browser based real-time communication open source project after purchasing Gips, which is highly recommended
After Google acquired Gips, it is the open source project of browser based real-time communication. Gips is the best audio transmission Library in the world at present, but its authorization fee is very high. Webrtc is a communication project that Google has opened after Google acquired Gips. Its core voiceengine is established by Gips. Therefore, the audio part of video conference can be realized by reference to webrtc.
Download address: http://www.webrtc.org
4. Openmeetings project
Reasons for listing: open source project of video conference based on Java browser, preferred for Java to develop video conference
Openmeetings is mainly based on OpenLaszlo streaming media format and red5 server open source video conference project. Its functions include audio and video, electronic whiteboard, etc. its project is developed in Java. The disadvantage of the project is that there are many bugs and low efficiency, but it can be used as a reference for flash video conference.
Download address: http://code.google.com/p/openmeetings/downloads/list
5. Live555 project
Reasons for listing: the heavy c++ streaming media open source project, some of which can be used as a reference for video conference development
Live555 is the most important c++ streaming media open source project, which includes not only the transmission protocol (SIP, RTP), audio and video encoder (H.264, MPEG4), but also the example of streaming media server. It is the first choice of streaming media project. The transmission module is very valuable for video conference development as reference.
Download address: http://www.live555.com/
6. Opal project
Reasons for listing: the next version of OpenH323, which contains SIP stack, is the first choice to implement SIP protocol
Opal is the next version of OpenH323, inheriting the OpenH323 protocol. It contains SIP stack. It is the first choice to implement SIP protocol, and the disadvantage is that there are few reference examples.
Download address: http://sourceforge.net/projects/opalvoip/files/
7. X264 project
Reasons for listing: the most widely used H.264 encoder is suitable for real-time video transmission
X264 is the most widely used H.264 encoder, which saves the low efficiency of H.264, and optimizes it. The efficiency is much higher than other open source H.264 projects, and it is the most suitable H.264 codec library for real-time video conference transmission.
Download address: http://www.x264.nl/
8. Speex project
Reasons for listing: the most famous open source project in audio field, narrow band and broadband have good voice quality
Speex is the most famous open source project in audio field. Both narrow band and broadband have good voice quality. It can transmit satisfactory language in 8KB. The disadvantage is that the quality of music will decrease when it is transmitted.
Download address: http://www.speex.org/downloads/
9. Jrtplib project
Reasons for listing: c++ cross platform RTP transmission open source project, RTP transmission Essential Library
Jrtplib is an open source project of c++ cross platform RTP transmission. It can be used to implement RTP protocol. Jrtplib is a necessary library for RTP transmission
Download address: http://research.edm.uhasselt.be/~jori/page/index.php?n=CS.Jrtplib
10. Xvid project
Reasons for listing: the most famous MPEG 4 encoder open source project, but less efficient than x264
Before H.264 coding protocol is not available, MPEG-4 encoding of XviD has always been the preferred video encoder for video conference. However, with the emergence of H.264 encoder with higher efficiency such as x264 and coreavc, its application effect is greatly impacted, but the video acquisition module combined with DirectShow is worth reference for video conference developers.
Download address: http://www.xvid.org
The development and selection of video conference transmission module
Video conference is mainly the software for audio video and data transmission. In these development, the core module is transmission module. The performance of transmission module directly affects the final quality of video conference. Therefore, the selection of transmission module is particularly important in video conference development. In the development process of transmission module, due to the influence of QoS, the technology of data retransmission is generally used. Therefore, the transmission module and the key point of video conference bottom development can be selected to develop directly with TCP and UDP or open source transmission library. Because some open source transmission libraries are mature, It can be used directly. If you develop the transmission module yourself, it is also a huge project. Now let's introduce the development options of the transmission module.
1. develop with TCP
The development of transmission module directly using TCP will not lose packets during transmission. We can use the completion port of oicp to communicate. The advantages are that QoS has guaranteed and supports large capacity data. The disadvantage is that the development cycle is long, the data establishment connection is much longer than that of ordinary UDP, and the resource consumption is larger than that of ordinary UDP transmission.
2. develop with UDP
UPD is a data report transmission mode, and its data can not guarantee the reliability of data in the transmission process. Therefore, the development of transmission module with UPD also involves the function of packet loss processing and automatic retransmission of QoS. The advantage of this method is that data transmission is faster than TCP, and the disadvantage is that the development cycle is long.
3. develop with UDT Library
UDT is built on UDP, and new congestion control and data reliability control mechanism are introduced. UDT is a two-way application layer protocol for connection. It supports reliable data flow transmission and partial reliable data packet transmission. UDT is characterized by that it can realize reliable data transmission without developing the transmission function of the library. The disadvantage is that the model is simple, and the port does not support large capacity data without oicp.
4. develop by ranknet Library
RakNet is also a c++ network library based on UDP network transport protocol. It can realize efficient network transmission service through the function of the library. It is applied in some game fields. Radnet can transmit 25000 messages per second between two programs; The advantage is that the function can be called directly without development. The disadvantage is that the traffic control failure caused by network congestion caused by the large amount of data transmission in public network.
In conclusion, the transmission module development of video conference has the highest transmission efficiency, but the development cycle is long. The transmission module developed by RakNet can not adapt to the transmission of big data. UDT has a good advantage in the transmission of large data, and the disadvantage is that not many concurrency is supported. However, UDT can also be concurrency with large capacity after modification, so it is the best choice to use UDT in video conference transmission module.
What is the decision of the clarity of video conference images
When we choose video conference, it is important to examine the stability of the system and the factors such as sound and video quality. What parameters are the parameters of video conference? First of all, the video quality is a subjective view of video image, which can not be systematized by a specific number. Therefore, we can only judge the definition of video conference image by subjective, and determine the definition of video conference by many factors, First, the most important is the video resolution of video conference, the other is video reduction quality of video conference encoder, and the image post-processing technology of the last video conference.
1. Video resolution
Video conference resolution is the resolution of the video collected image of video conference. This parameter plays an important role in the definition measurement of video conference. The resolution of video conference can be divided into QCIF (160 * 120), CIF (320 * 240), 720p (1280 * 720), 1280P (1920 * 1280), and the higher the resolution, the clearer the image display, The market said high-definition video conference system, that is, the image acquisition resolution reaches 720p or more high-definition resolution. But not the higher the resolution, the higher the video quality of video conferencing? The answer is No. The resolution of video conference is only the image acquisition resolution, and video conference system needs to be encoded, decoded and processed later. Therefore, the higher the resolution of video conference is not equal to the higher the video quality of video conference, only local video quality increases with the increase of image acquisition resolution. Figure 1 is an image with various resolutions. We also have a lot of mistakes about HD cameras. Some manufacturers mark their cameras with very high pixels. Everyone thinks this is definitely high-definition resolution. But when testing, we find that the resolution of the camera is only 640 * 480. This kind of camera is not a HD camera head. The most basic index of high-definition camera is 720p resolution. Therefore, the resolution of image acquisition is the decisive factor of HD camera.
2. The quality of video coding restoration
Video coding quality is also an important indicator of video conference definition. For example, the most popular H.264 coding has higher coding quality and better image restoration ability than the previous MPEG4 reduction ability. After that image is restored by different video coding, the image restoration degree is different. We first talk about the video coding process. Video coding first obtains the image of the video acquisition equipment, then divides the image into several blocks, and then converts the blocks into digital ones. The purpose of the image restoration is achieved by predicting the block within the frame and prediction out of frame. Therefore, the smaller the block of the image, the higher the image restoration degree, For example, H.264 uses at least 4 * 4 blocks for block prediction, while MPEG 4 and H.263 use blocks with minimum 8 * 8 and 16 * 16 to predict and restore. Therefore, h.264 encoded images are clearer than MPEG 4 and H.263 under the same data transmission rate. Therefore, the clarity of video conference is also related to the quality of video coding restoration.
3. Video conference image post-processing technology
The definition of video conference image is also related to the post-processing technology of image. Different video conference systems have different post-processing technologies for images. Some video conferences add image filtering to the image, so as to remove the square effect of image restoration. Some video conference software uses image enhancement technology for images, making the image look clearer.
The above is the most important three aspects to determine the definition of video conference. Video conference resolution is the key factor to determine the local video quality. Video coding is the most important factor to determine the energy of video restoration in the process of coding and decoding. Image post-processing technology is the post-processing of image restoration, and plays an important role in video conference.
Libav, ffmpeg, Mplayer, VLC open source project, ffdshow
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How far(long) the transmitter cover?
The transmission range depends on many factors. The true distance is based on the antenna installing height , antenna gain, using environment like building and other obstructions , sensitivity of the receiver, antenna of the receiver . Installing antenna more high and using in the countryside , the distance will much more far.
EXAMPLE 5W FM Transmitter use in the city and hometown:
I have a USA customer use 5W fm transmitter with GP antenna in his hometown ,and he test it with a car, it cover 10km(6.21mile).
I test the 5W fm transmitter with GP antenna in my hometown ,it cover about 2km(1.24mile).
I test the 5W fm transmitter with GP antenna in Guangzhou city ,it cover about only 300meter(984ft).
Below are the approximate range of different power FM Transmitters. ( The range is diameter )
0.1W ~ 5W FM Transmitter ：100M ~1KM
5W ~15W FM Ttransmitter : 1KM ~ 3KM
15W ~ 80W FM Transmitter : 3KM ~10KM
80W ~500W FM Transmitter : 10KM ~30KM
500W ~1000W FM Transmitter : 30KM ~ 50KM
1KW ~ 2KW FM Transmitter : 50KM ~100KM
2KW ~5KW FM Transmitter : 100KM ~150KM
5KW ~10KW FM Transmitter : 150KM ~200KM
How to contact us for the transmitter?
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1.How far you want to cover in diameter ?
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