A few days ago, I spent some time to study HTTP live streaming (HLS) technology and implement an HLS encoder, hlsliveencoder, written in C + +. Its function is to capture the camera and microphone, real-time H.264 video coding and aac audio coding, and according to the HLS protocol specification, generate segmented standard TS file and m3u8 index file. Through my hlsliveencoder and the third-party HTTP server (such as nginx), we successfully realized the live streaming of HTTP and passed the test on the iPhone. I will write some of the gains here.
1. Analysis of HLS Technology
HTTP live streaming (HLS) is a streaming media transport protocol based on HTTP implemented by Apple Inc., which can realize live and on-demand streaming media. It is mainly used in IOS system to provide audio and video live and on-demand solutions for IOS devices (such as iPhone and iPad). HLS on demand is basically a common segmented HTTP on demand. The difference is that its segments are very small. In order to realize HLS on demand, the key is to segment media files. At present, there are many open source tools that can be used. I will not discuss it here, just talk about HLS live broadcast technology.
Compared with the common live streaming protocols, such as RTMP protocol, RTSP protocol, MMS protocol and so on, the biggest difference of HLS live streaming is that the live client does not get a complete data stream. HLS protocol stores the live data stream as continuous, short-term and long media files (mpeg-ts format) on the server side, while the client side continuously downloads and plays these small files, because the server side always generates new small files from the latest live data, so that the client side only needs to play the files obtained from the server in order to realize the live. It can be seen that HLS basically realizes live broadcasting by means of VOD technology. Because the data is transmitted through HTTP protocol, there is no need to consider the problem of firewall or proxy, and the time of segmenting files is very short. The client can quickly select and switch the code rate to adapt to the playback under different bandwidth conditions. However, due to the technical characteristics of HLS, its delay is always higher than that of ordinary live streaming protocol.
According to the above understanding, to achieve HTTP live streaming live, we need to study and implement the following key technologies.
(1) Collect the data of video source and audio source
(2) The original data is encoded by H264 and AAC
(3) Video and audio data are packaged as mpeg-ts packets
(4) HLS segmentation generation strategy and m3u8 index file
2. HTTP transport protocol
Among them, the first and second points have been mentioned in my previous article, and the last point is that we can use the existing HTTP server, so the implementation of the third and fourth points is the key.
(1) Program framework and Implementation
Through the above analysis, the logic and process of HLS live encoder are basically clear: start the audio and video coding thread respectively, realize the audio and video acquisition through DirectShow (or other) technology, and then call libx264 and libfaac respectively for video and audio coding. After the two encoding threads encode the audio and video data in real time, they store it in a segment file of mpeg-ts format according to the customized partition strategy. When a segment file is stored, the m3u8 index file is updated. As shown in the figure below:
In the figure above, after receiving the video and audio data, hlsliveencoder needs to first determine whether the current partition should end, and create a new partition to continue the continuous generation of TS partition. It should be noted that the new fragmentation should start from the key frame to prevent the player from decoding failure. The core code is as follows:
The interface of tsmuxer is also relatively simple.
(2) HLS segment generation strategy and m3u8
① Segmentation strategy
The segmentation strategy of HLS is basically recommended to split every 10 seconds. Of course, the specific time should be marked according to the actual length of the split
Generally speaking, for the sake of cache and other reasons, the latest three fragment addresses are kept in the index file and updated in the form of "sliding window".
② Introduction of m3u8 file
M3u8 is the index file of HTTP live streaming. M3u8 can be regarded as. M3U format file basically, the difference is that m3u8 file uses UTF-8 character encoding.
Copy code
#Extm3u M3U file header, must be placed in the first line
#Serial number of the first TS segment of ext-x-media-sequence
#Ext-x-targetduration the maximum duration of each TS segment
#Does ext-x-allow-cache allow cache
#End of ext-x-endlist m3u8 file
#Extinf extra info, the information of split ts, such as duration, bandwidth, etc
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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
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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.
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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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