The challenge of mobile live broadcasting technology is far from traditional equipment or computer live broadcast. Its complete processing links include but not limited to: audio and video acquisition, beauty / filter / special effect processing, coding, packet, streaming, transcoding, distribution, decoding / rendering / playing, etc.
The common problems of live broadcasting include:
How can the host stream be stable in the unstable network environment?
How can the audience in remote areas watch the live broadcast smoothly in high definition?
How to switch the line intelligently in the instant of live card?
How to measure the accuracy of the live broadcast quality index and adjust it in real time?
How can different chip platforms on mobile devices encode and render video with high performance?
How to deal with the special effects of filters such as beauty?
How to realize the second on of playback?
How to ensure the continuous broadcast of live broadcast smooth without carding?
This sharing will unveil the mystery of the core technology of mobile broadcast.
1. Basic knowledge of video, live broadcast and so on
What is video?
First, we need to understand one of the most basic concepts: video. From the perceptual point of view, video is a film full of fun, can be a film, can be a short film, is a coherent visual impact performance rich picture and audio. But from a rational point of view, video is a structured data. It can be interpreted in engineering language. We can analyze video into the following structure:
1)Experience of second on Optimization of mobile live broadcast technology (including ppt)
2)Content element
3)Image
4)Audio
5)Meta information
6)Codec
Video : H.264，H.265, …
Audio : AAC， HE-AAC, …
7)Container
MP4，MOV，FLV，RM，RMVB，AVI，…
Any video video file, structurally, is such a way of composition:
1)The most basic content elements are composed of image and audio;
2)The image is processed by video coding and compression format (usually H.264);
3)Audio is processed by audio coding compression format (such as AAC);
4)Indicate the corresponding meta information (metadata);
Finally, the container package (such as MP4) is completed to form a complete video file.
If you feel it's hard to understand, imagine a bottle of ketchup. The outer layer bottle is like the container, the raw materials and processing plant information indicated on the bottle are like metadata. After the bottle cap is opened (unpacked), the ketchup itself is like the encoded content after compression processing. The process of tomato and seasoning processing into ketchup is like coding, while the raw material tomato and seasoning are the most similar to the most The original content element.
2. Real time transmission of video
In short, rational cognitive video structure helps us understand video broadcast. If video is a kind of structured data, then video broadcast is undoubtedly the way to transmit this "structured data" (video) in real time.
So the obvious question is: how can real time transmit this structured data?
Here is a paradox: a container packaged video must be immutable video file, immutable video file is already a production result, according to "relativity", and this production result can not be accurate to the real-time level, it has been a memory of time and space.
Therefore, video broadcast must be a process of "production, transmission and consumption". This means that we need to take a closer look at the middle process (coding) of video before the original content elements (images and audio) to the finished product (video files).
3. Video coding compression
Let's take a look at video coding and compression technology.
In order to facilitate the storage and transmission of video content, it is usually necessary to reduce the volume of video content, that is, the original content elements (image and audio) need to be compressed, and the compression algorithm is also referred to as the coding format. For example, the original image data in the video will be compressed in H.264 encoding format, and the audio sampling data will be compressed in AAC encoding format.
After encoding and compressing, video content is really conducive to storage and transmission; however, when watching and playing, decoding process is also needed accordingly. Therefore, it is obvious that a kind of convention can be understood by both encoder and decoder is required between encoding and decoding. In terms of video image coding and decoding, this Convention is simple:
The encoder encodes multiple images and produces a GOP (group of pictures) in a segment. When playing, the decoder reads a section of GOP for decoding, then reads the picture and then renders the display.
Experience of second on Optimization of mobile live broadcast technology (including ppt)
GOP (group of pictures) is a series of continuous pictures, which consists of one I frame and several B / P frames. It is the basic unit of video image encoder and decoder access. Its arrangement sequence will be repeated until the end of image.
Experience of second on Optimization of mobile live broadcast technology (including ppt)
I frame is an internal coding frame (also known as keyframe), P frame is forward prediction frame (forward reference frame), and frame B is bidirectional interpolation frame (bidirectional reference frame). In short, frame I is a complete picture, while P and B record changes relative to I frame.
Without I frames, P and B frames cannot be decoded.
Experience of second on Optimization of mobile live broadcast technology (including ppt)
In summary, a video whose image part data is a set of GOPs, while a single GOP is a set of I / P / B frame images.
In such a geometric relationship, video is like an "object", GOP is like "molecule", and the image of I / P / B frame is like "atom".
Imagine what would be an experience if we changed the transmission of an object to an atom, and the smallest particle at the speed of light, and perceived with the naked eye of human beings?
4. What is video live?
It is not difficult to open the brain hole, live broadcast is such an experience. Video live technology is the smallest particle (I / P / B frame ）, a technology for transmission at the speed of light based on time series.
In short, live broadcast is the process of streaming data (video / audio / data frame) and time stamp. The transmitter continuously collects audio and video data, then spreads through coding, packet, push flow, and then spreads through relay distribution network. The playback end downloads data continuously and decodes and plays according to time sequence. In this way, the live broadcast process of "production, transmission and consumption" is realized.
After understanding the above two basic concepts about video and live broadcast, we can see the business logic of live broadcast.
Business logic of live broadcast
Here is a streamlined one to many live service model, as well as protocols between different levels.
Experience of second on Optimization of mobile live broadcast technology (including ppt)
The differences between the agreements are as follows
Experience of second on Optimization of mobile live broadcast technology (including ppt)
Experience of second on Optimization of mobile live broadcast technology (including ppt)
Above are some basic concepts about live broadcast technology. Next we further understand the live performance indicators that affect people's visual experience.
Performance index of live broadcast affecting visual experience
The first performance indicator of live broadcast is delay, which is the time required for data to be sent from the information source to the destination.
Experience of second on Optimization of mobile live broadcast technology (including ppt)
According to Einstein's narrow relativity, the speed of light is the highest speed that all energy, matter and information can achieve. This conclusion sets a limit to the speed of transmission. So even if we feel real-time with the naked eye, there is actually a certain delay.
Experience of second on Optimization of mobile live broadcast technology (including ppt)
Because rtmp/hls is based on the application layer protocol over TCP, TCP handshakes three times, four waves, and every round trip in the slow start process will be added with a round trip time (RTT), which will increase the delay.
Experience of second on Optimization of mobile live broadcast technology (including ppt)
Secondly, according to the characteristics of TCP packet loss retransmission, network jitter may cause packet loss retransmission, and also indirectly lead to the increase of delay.
Experience of second on Optimization of mobile live broadcast technology (including ppt)
A complete live broadcast process includes but is not limited to the following links: collection, processing, coding, packet, streaming, transmission, transcoding, distribution, streaming, decoding and playback. From streaming to playing, and then through the intermediate forwarding link, the lower the delay, the better the user experience.
The second performance indicator of live broadcast is the display frame lag in the video playback process, which makes people feel "card". The statistics of the number of hits played in unit time is called the carting rate.
The factors that cause the Caton may be the data interruption of the streaming end, the congestion of public network transmission or abnormal network jitter, or the poor decoding performance of terminal devices. The less or no Caton frequency, the better the user experience.
The first screen of the third live performance indicator is time consuming, which refers to the time that the screen is waiting for the naked eye to see after the first click and play. Technically, it refers to the time consuming for the player to decode the first frame of rendering display. Generally speaking, "second on" refers to the screen can be seen within one second after clicking on the playback. The faster the first screen opens, the better the user experience.
The above three live broadcast performance indicators correspond to a low latency, high-definition smooth, fast second on user experience requirements. Understanding these three performance indicators is very important to optimize the user experience of mobile live app.
So what are the common pits in mobile live broadcast?
According to the experience summarized in practice, the pit of video live broadcast on mobile platform can be summarized into two aspects: equipment difference and technical test brought by these scenes in network environment.
The pit and avoidance measures of mobile live broadcast scene
Coding differences on different chip platforms
Experience of second on Optimization of mobile live broadcast technology (including ppt)
No matter hard or soft coding on IOS platform, because it is a factory of apple, there is almost no coding difference due to different chip platforms.
However, on Android platform, the mediacodec encoder provided by Android framework SDK has great differences on different chip platforms. Different manufacturers use different chips, while Android mediacodec performance is slightly different on different chip platforms, and the cost of realizing the compatibility of the whole platform is not low.
In addition, the H.264 coding quality parameters of Android mediacodec hard coding layer are fixed based, so the quality of painting is usually also general. Therefore, under Android platform, the recommendation is to use soft editing, the advantage is that the painting quality can be regulated and the compatibility is better.
How to collect and code low-end equipment with high performance?
Experience of second on Optimization of mobile live broadcast technology (including ppt)
For example, camera may be the picture. The volume of a picture is not small. If the frequency of acquisition is very high and the frame rate of coding is very high, each picture passes through the encoder, the encoder may overload again.
At this time, we can consider that before coding, without affecting the quality of the picture (we have talked about the micro significance of frame rate), we can selectively lose frames, so as to reduce the power consumption of the coding link.
How to guarantee high definition smooth streaming under weak network
Experience of second on Optimization of mobile live broadcast technology (including ppt)
In mobile network, it is easy to encounter network instability, connection reset, broken line reconnection, on the one hand, frequent reconnection, and the establishment of connection requires overhead. On the other hand, bandwidth bottleneck may occur especially when GPRS / 2G / 3G / 4G switch occurs. When the bandwidth is not enough, the content with high frame rate / high bit rate is difficult to send out, so variable bit rate support is needed.
That is, at the push end, the network state and simple speed measurement can be detected, and the code rate can be switched dynamically to ensure the smooth flow of the push during network switching.
Secondly, the logic of coding, packet and push stream can also be fine tuned. You can try to lose frames selectively, such as losing the video reference frame first (I frame and audio frame), which can also reduce the data content to be transmitted, but at the same time, it can achieve the purpose of not affecting the quality of painting and smooth audio-visual version.
The status and business status of live stream need to be distinguished
Live broadcast is the interaction of media stream and app is API signaling stream, and the status of both cannot be confused. In particular, the status of live stream cannot be judged based on the API state of APP interaction.
Experience of second on Optimization of mobile live broadcast technology (including ppt)
The above are several common pits and avoidance measures in the live mobile scene.
Other optimization measures for mobile live broadcast scene
1、 How to optimize the opening speed to reach the legendary "second on"?
You may see that some mobile phone live app on the market is very fast on, a little on. And some mobile phones live app, click to play after several seconds before playing. What causes such a difference?
Most players can decode and play after they get a completed GOP. Ffmpeg based players can play only after the time stamp synchronization of audio and painting is needed (if there is no audio in a live broadcast, only video can play the face after waiting for the audio timeout).
The second on can be considered in the following aspects:
1. rewrite the player logic to display the player after it gets the first key frame.
The first frame of GOP is usually keyframe, and it can reach "first frame second on" because of the less data loaded.
If the live server supports GOP cache, it means that the player can get the data immediately after establishing a connection with the server, thus saving the time of back source transmission across regions and across operators.
GOP reflects the period of keyframes, that is, the distance between two keyframes, namely the maximum number of frames in a frame group. Assuming that the constant frame rate of a video is 24fps (i.e. 1 second 24 frames) and the keyframe period is 2S, then a GOP is 48 images. In general, at least one keyframe is required for each second of video.
Increasing the number of keyframes improves the quality of the picture (GOP is usually a multiple of FPS), but increases the bandwidth and network load at the same time. This means that the client player downloads a GOP.
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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]
Our Factory
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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This is our participation in 2012 Global Sources Hong Kong Electronics Fair . Customers from all over the world finally have a chance to get together.
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 .
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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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