Recently began to contact the video live project, I also summarized some video live related concepts, technologies and solutions.
First of all, understand the concept of live video. Several common video protocols are: RTMP, http-flv, HLS, RTP / RTCP.
Then we will explain the whole process of live broadcasting and related technologies.
1、 Live video protocol
In the field of live broadcasting, there are two types of live broadcasting: interactive live broadcasting and non interactive live broadcasting.
Non interactive live broadcasting (such as: Live parade, NBA Live Broadcasting, Champions League live broadcasting, etc.) is not highly interactive, allowing a delay of 10 seconds or more. It is characterized by relatively few sources and suitable for multi-channel transcoding (users can watch it according to network conditions).
The typical scenes of interactive live broadcasting include show live broadcasting, game live broadcasting, etc. Because of the high requirements for the interaction between the anchor and the audience, these live broadcasts are required to be delayed within 5S. The characteristics of interactive live broadcasting are: more sources, not suitable for multi-channel transcoding, intermediate server only as a transit role.
The media of live content transmission is the network, and the corresponding protocols are needed to transmit video or audio in the network. At present, the common protocols suitable for live scenes are as follows.
1. RTMP protocol (not supported by HTML 5, supported by flash)
RTMP is a streaming media protocol, which is Adobe's patent protocol. Based on TCP, it is very popular in China.
Popular reason: the support of open source software and open source library is stable and complete, and the most commonly used streaming and streaming solutions can basically run stably. For example: open source librtmp push stream library, service side has nginx RTMP plug-in, pull stream has ijkplayer play library.
2. Http-flv protocol (not supported by HTML 5, supported by flash)
That is to use HTTP protocol to stream media content. HTTP is simpler and better known than RTMP. The content delay can also be 2-5 seconds, and the opening speed is faster, because HTTP itself has no complex state interaction. So from the perspective of latency, http-flv is better than RTMP.
3. HLS protocol (HTML support, Flash support)
HTTP live streaming is a streaming media transport protocol based on HTTP proposed by apple. HLS has a very big advantage: HTML5 can be directly opened and played; this means that a live link can be shared through wechat and other forwarding, without the need to install any independent app, with a browser, so it is very popular. Social live app, HLS is just needed. The live stream URL based on HLS is an m3u8 file, which contains several recent small video TS files. The delay of this playback mode is relatively high (which is related to the size of TS file), and it can achieve 5-7 seconds delay in the same city network.
4. RTP / RTCP protocol
Real time transport protocol is a transport layer protocol for multimedia data stream on Internet. RTCP transmits the signaling of interactive control and RTP transmits the actual media data.
RTP is widely used in video surveillance, video conference and IP phone, because one of the important experience of video conference and IP phone is strong real-time content.
Compared with the above three protocols, one important difference between RTP and them is that UDP protocol is used to transmit data by default, while RTMP and HTTP are based on TCP protocol.
Use scenario analysis: the scene of real-time audio and video stream does not need reliable guarantee, so there is no need to have a retransmission mechanism. It is not important to see the image and sound in real time, lose some content when the network jitters, blur the picture and splash screen. In order to retransmit, TCP will cause delay and asynchrony. If a certain section of content arrives after one second due to retransmission, then the whole conversation will be delayed by one second. With the network jitter, the delay will increase to two seconds or three seconds. If the client does not handle the playback, the direct broadcast experience will be seriously affected. How to optimize, will be explained in the following article.
Conclusion: in the selection of live broadcast protocol, if RTMP or http-flv is selected, it means that there is a content delay of 2-5 seconds, but as far as the open delay is concerned, http-flv is better than RTMP. HLS has a content delay of 5-7 seconds. Choosing RTP for live broadcast can delay the live broadcast within 1 second. However, as far as we know, the major CDN manufacturers do not support live broadcast based on RTP, so the current domestic mainstream is RTMP or http-flv.
2、 Video live broadcast process
The technical process related to live video is: real-time video stream acquisition --- video stream coding --- video stream transmission --- video stream decoding --- video playing.
1. The idea of real-time video capture
a) By setting setpreviewcallback in Android camera shooting preview, the onpreviewframe interface is realized to capture the data of each video stream in real time.
b) Through Android mediarecorder, bind localsocket in setoutputfile function.
c) Streaming media server mode, using ffmpeg or getstreamer to get camera video.
2. The realization of video compression coding
a) Without encoding, the original yuv420sp video frame is transmitted directly through socket.
b) JEPG compresses the original yuv420sp video frame into H.264 and then transmits it.
c) H.264/avc. The original yuv420sp video frame is compressed into H.264 and then transmitted. Common open source encoders based on H264 include JM, x264, t264, hdot264, etc
d) . mpeg4. Compress the original yuv420sp video frame into MPEG4 and then transmit
3. The idea of video transmission
a) . socket transmission
b) . HTTP transport
c) . RTP / RTSP transmission
d) . streaming media server mode, such as live555, etc
4. The realization of video decoding
a) . decoder corresponding to encoding
5. The idea of video playing
a) . through Android videoview
b) . via Android mediaplay
c) . paste frame image directly through canvas
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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?
Call me +8618078869184 OR
Email me [email protected]
1.How far you want to cover in diameter ?
2.How tall of you tower ?
3.Where are you from ?
And we will give you more professional advice.
About Us
FMUSER.ORG is a system integration company focusing on RF wireless transmission / studio video audio equipment / streaming and data processing .We are providing everything from advice and consultancy through rack integration to installation, commissioning and training.
We offer FM Transmitter, Analog TV Transmitter, Digital TV transmitter, VHF UHF Transmitter, Antennas, Coaxial Cable Connectors, STL, On Air Processing, Broadcast Products for the Studio, RF Signal Monitoring, RDS Encoders, Audio Processors and Remote Site Control Units, IPTV Products, Video / Audio Encoder / Decoder, designed to meet the needs of both large international broadcast networks and small private stations alike.
Our solution has FM Radio Station / Analog TV Station / Digital TV Station / Audio Video Studio Equipment / Studio Transmitter Link / Transmitter Telemetry System / Hotel TV System / IPTV Live Broadcasting / Streaming Live Broadcast / Video Conference / CATV Broadcasting system.
We are using advanced technology products for all the systems, because we know the high reliability and high performance are so important for the system and solution . At the same time we also have to make sure our products system with a very reasonable price.
We have customers of public and commercial broadcasters, telecom operators and regulation authorities , and we also offer solution and products to many hundreds of smaller, local and community broadcasters .
FMUSER.ORG has been exporting more than 15 years and have clients all over the world. With 13 years experience in this field ,we have a professional team to solve customer's all kinds of problems. We dedicated in supplying the extremely reasonable pricing of professional products & services. Contact email : [email protected]
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We have modernization of the factory . You are welcome to visit our factory when you come to China.
At present , there are already 1095 customers around the world visited our Guangzhou Tianhe office . If you come to China , you are welcome to visit us .
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Where is Fmuser ?
You can search this numbers " 23.127460034623816,113.33224654197693 " in google map , then you can find our fmuser office .
FMUSER Guangzhou office is in Tianhe District which is the center of the Canton . Very near to the Canton Fair , guangzhou railway station, xiaobei road and dashatou , only need 10 minutes if take TAXI . Welcome friends around the world to visit and negotiate .
Contact: Sky Blue
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English: We accept all payments , such as PayPal, Credit Card, Western Union, Alipay, Money Bookers, T/T, LC, DP, DA, OA, Payoneer, If you have any question , please contact me [email protected] or WhatsApp +8618078869184
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For Warranty .
Contact US--->>Return the item to us--->>Receive and send another replace .
Name: Liu xiaoxia
Address: 305Fang HuiLanGe HuangPuDaDaoXi 273Hao TianHeQu Guangzhou China.
ZIP:510620
Phone: +8618078869184
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