Simply put, I-frames are key frames and belong to intra-frame compression. It is the same as AVI compression. P means to search forward. B is two-way search. They are all based on I frame to compress data.
The I frame represents the key frame, which you can understand as the complete preservation of this frame of picture; only this frame of data is needed for decoding (because it contains the complete picture)
P frame represents the difference between this frame and the previous key frame (or P frame). When decoding, the difference defined by this frame needs to be superimposed on the previously buffered picture to generate the final picture. (That is, the difference frame, P frame does not have complete picture data, only data that is different from the picture of the previous frame)
The B frame is a two-way difference frame, that is, the B frame records the difference between the current frame and the previous and next frames (the specifics are more complicated, there are 4 cases), in other words, to decode the B frame, you must not only obtain the previous buffered picture, but also decode For the subsequent screens, the final screen is obtained by superimposing the front and back screens with the data of the current frame. The B frame has a high compression rate, but the CPU will be more tired during decoding.
Compression method used:
Grouping: Divide several frames into a group (GOP). In order to prevent motion changes, the number of frames should not be too large.
1) Defining frame: Define each frame image in each group as three types, namely I frame, B frame and P frame;
2) Predicted frame: I frame is used as the basic frame, P frame is predicted by I frame, and B frame is predicted by I frame and P frame;
3) Data transmission: Finally, the difference between the I frame data and the predicted information is stored and transmitted.
1. I frame
I images (frames) are intra-frame coded images that compress the amount of transmitted data by removing the image*** spatial redundant information*** as much as possible.
I frame is also called ***intra picture***, I frame is usually the first frame of each GOP (a video compression technology used by MPEG), after moderate compression (as random The reference point of the visit) can be regarded as an image. In the process of MPEG encoding, some video frame sequences are compressed into I frames, some are compressed into P frames, and some are compressed into B frames. The I-frame method is the *** intra-frame compression method (P and B are inter-frame)***, also known as the *** "key frame" *** compression method. The I-frame method is a compression technology based on the Discrete Cosine Transform (DCT), which is similar to the JPEG compression algorithm. Using I frame compression can reach a compression ratio of 1/6 without obvious compression traces.
1.1 Features of I frame:
1) It is a full-frame compression coded frame. It performs JPEG compression encoding and transmission of full frame image information;
2) The complete image can be reconstructed by using only the data of the I frame during decoding;
3) The I frame describes the details of the image background and the moving subject;
4) I frames are generated without referring to other pictures;
5) I frame is the reference frame of P frame and B frame (its quality directly affects the quality of subsequent frames in the same group);
6) The I frame is the basic frame (the first frame) of the GOP of the frame group, and there is only one I frame in a group;
7) I frame does not need to consider motion vector;
8) The amount of information in the data occupied by the I frame is relatively large.
1.2 I frame encoding process:
(1) Perform intra-frame prediction and determine the intra-frame prediction mode used.
(2) The predicted value is subtracted from the pixel value to obtain the residual.
(3) Transform and quantize the residual.
(4) Variable length coding and arithmetic coding.
(5) The image is reconstructed and filtered, and the obtained image is used as a reference frame for other frames.
2. P frame
A P picture (frame) is a coded picture that compresses the amount of transmitted data by sufficiently reducing the temporal redundant information of the previously coded frame in the picture sequence, also called a ***predicted frame***.
When encoding continuous dynamic images, the continuous images are divided into three types: P, B, and I. The P frame is predicted from the P frame or I frame in front of it, and it is compared with the P frame or I frame in front of it. The same information or data between the two, that is, consider the characteristics of motion for inter-frame compression. The P frame method compresses the data of the current frame according to the difference between the current frame and the adjacent previous frame (I frame or P frame). Adopting the method of joint compression of P-frame and I-frame can achieve higher compression without obvious compression traces.
1) Prediction and reconstruction of P frames:
P frame uses I frame as a reference frame, find out the prediction value and motion vector of P frame "a certain point" in I frame, and transmit the prediction difference and motion vector together. At the receiving end, according to the motion vector, the predicted value of "a certain point" of the P frame is found from the I frame and added with the difference to obtain the sample value of the "certain point" of the P frame, so that a complete P frame can be obtained.
2) Features of P frame:
① P frame is a coded frame separated by 1-2 frames after I frame.
②P frame uses motion compensation to transmit the difference between it and the previous I or P frame and the motion vector (prediction error).
③When decoding, the predicted value in the I frame and the prediction error must be summed to reconstruct the complete P frame image.
④ The P frame belongs to the inter-frame coding of forward prediction. It only refers to the previous I-frame or P-frame closest to it.
⑤ The P frame can be the reference frame of the P frame after it, or the reference frame of the B frame before and after it.
⑥Because the P frame is a reference frame, it may cause the spread of decoding errors.
⑦Because it is a differential transmission, the compression of P frames is relatively high.
3. B frame
B image (frame) is a coded image that takes into account both the coded frames before the source image sequence and the time redundant information between the coded frames after the source image sequence to compress the amount of transmission data, also called *** bidirectional predictive frame ***.
The B-frame method is an inter-frame compression algorithm for bidirectional prediction. When compressing a frame into a B frame, it compresses the frame according to the different points of the adjacent previous frame, the current frame and the next frame, that is, only the difference between the current frame and the previous frame is recorded* **. Only by using B-frame compression can a high compression of 200:1 be achieved. Generally, I frame has the lowest compression efficiency, P frame is higher, and B frame is the highest.
1) Prediction and reconstruction of B frames:
The B frame uses the preceding I or P frame and the following P frame as reference frames to "find out" the predicted value and two motion vectors of a "point" in the B frame, and then take the prediction difference and the motion vector for transmission. The receiving end "finds (calculates)" the predicted value in the two reference frames according to the motion vector and sums it with the difference to obtain the "some point" sample value of the B frame, so that the complete B frame can be obtained.
2) Features of B frame:
① The B frame is predicted by the preceding I or P frame and the following P frame;
② The B frame transmits the prediction error and motion vector between it and the preceding I or P frame and the following P frame;
③ B frame is a two-way predictive coding frame;
④ The B frame has the highest compression ratio, because it only reflects the changes of the moving subject between the 2 reference frames, and the prediction is more accurate;
⑤ The B frame is not a reference frame and will not cause the spread of decoding errors.
4. The basic process of P frame and B frame encoding is:
(1) Perform motion estimation and calculate the rate-distortion function (section) value of the inter-frame coding mode. P frame only refers to the previous frame, and B frame can refer to the following frame.
(2) Perform intra-frame prediction, select the intra-frame mode with the smallest rate-distortion function value and compare it with the inter-frame mode to determine which coding mode to use.
(3) Calculate the difference between the actual value and the predicted value.
(4) Transform and quantize the residual.
(5) If encoding, if it is an inter-frame encoding mode, encode a motion vector.
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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 .
At Fair
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 .
Contact: Sky Blue
Cellphone: +8618078869184
WhatsApp: +8618078869184
Wechat: +8618078869184
E-mail: [email protected]
QQ: 727926717
Skype: sky198710021
Address: No.305 Room HuiLan Building No.273 Huanpu Road Guangzhou China Zip:510620
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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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We recommend you use Paypal to buy our items ,The Paypal is a secure way to buy on internet .
Every of our item list page bottom on top have a paypal logo to pay.
Credit Card.If you do not have paypal,but you have credit card,you also can click the Yellow PayPal button to pay with your credit card.
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But if you have not a credit card and not have a paypal account or difficult to got a paypal accout ,You can use the following:
Western Union.  www.westernunion.com
Pay by Western Union to me :
First name/Given name: Yingfeng
Last name/Surname/ Family name: Zhang
Full name: Yingfeng Zhang
Country: China
City: Guangzhou
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T/T . Pay by T/T (wire transfer/ Telegraphic Transfer/ Bank Transfer)
First BANK INFORMATION (COMPANY ACCOUNT):
SWIFT BIC: BKCHHKHHXXX
Bank name: BANK OF CHINA (HONG KONG) LIMITED, HONG KONG
Bank Address: BANK OF CHINA TOWER, 1 GARDEN ROAD, CENTRAL, HONG KONG
BANK CODE: 012
Account Name : FMUSER INTERNATIONAL GROUP LIMITED
Account NO. : 012-676-2-007855-0
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Second BANK INFORMATION (COMPANY ACCOUNT):
Beneficiary: Fmuser International Group Inc
Account Number: 44050158090900000337
Beneficiary's Bank: China Construction Bank Guangdong Branch
SWIFT Code: PCBCCNBJGDX
Address: NO.553 Tianhe Road, Guangzhou, Guangdong,Tianhe District, China
**Note: When you transfer money to our bank account, please DO NOT write anything in the remark area, otherwise we won't be able to receive the payment due to government policy on international trade business.
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* It will be sent in 1-2 working days when payment clear.
* We will send it to your paypal address. If you want to change address, please send your correct address and phone number to my email [email protected]
* If the packages is below 2kg,we will be shipped via post airmail, it will take about 15-25days to your hand.
If the package is more than 2kg,we will ship via EMS , DHL , UPS, Fedex fast express delivery,it will take about 7~15days to your hand.
If the package more than 100kg , we will send via DHL or air freight. It will take about 3~7days to your hand.
All the packages are form China guangzhou.
* Package will be sent as a "gift" and declear as less as possible,buyer don't need to pay for "TAX".
* After ship, we will send you an E-mail and give you the tracking number.
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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
Please return to this address and write your paypal address,name,problem on note: |
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