Abstract: Television equipment is gradually transitioning from analog to digital. Companies such as SONY, Panasonic, and JVC have introduced the latest digital camera, recording, and editing equipment. In today's television technology field, digital recording and editing have been widely used.
At present, television equipment is gradually transitioning from analog to digital. Companies such as SONY, Panasonic, JVC have introduced the latest digital video, recording, and editing equipment. In today's television technology field, digital recording and editing have been widely used.
There are two major types of digital video recording formats: uncompressed and compressed. The D1, D2, D3, D5 series of non-compressed recording formats, which directly record the input signal at the original signal rate, maintain the original level of the signal, and are lossless recording. The recording method is divided into digital component (D1, D5) and digital composite (D2, D3). They represent the highest standard of video equipment, with the highest image quality and the smallest signal loss. The requirements are extremely demanding and the price is very expensive. Although the product has been available for several years, it is only used by a few video production companies that require extremely high image quality. The compression format refers to the video that adopts digital compression technology. The common ones are DV, MPEG-2, M-JPEG, etc., and various data compression standards have been formulated, so the corresponding digital Betacam (DVW), DV, DVCPRO, DIGITAL -S, DVCAM, Betacam-SX and other specifications of digital video recorders, they compress the image signal and then record it on the tape, the purpose of which is to reduce the data volume of the image signal, reduce the volume of the device, and reduce the size of the image signal while ensuring the image quality. The amount of tape to achieve the best possible effect with the smallest signal loss, thereby reducing equipment costs.
1. International standards of digital video technology
(1) Recommendation No. CCIR601
In order to facilitate international program exchange, eliminate the standard differences between digital equipment, and make the 625-line TV system compatible with the 525-line TV system, the International Radio Consultative Committee (CCIR, now renamed ITU Radio) in February 1982 The Ministry of Communications, namely ITU-R) adopted Recommendation No. 601 at the 15th plenary meeting, and determined to be based on component coding: coding based on the luminance component Y and two color difference components RY and BY as the digital coding of the TV studio International standards.
(2) H.261 standard
H.261 is abbreviated as p×64. This standard is used for video telephony and video conferencing. The image coding algorithm is real-time processing, and the delay time is minimal, so that the image and voice are closely matched to achieve full-color real-time motion video transmission and obtain a high compression ratio. The standard was passed by the International Telegraph and Telephone Consultative Committee (CCITT) in 1990.
(3) JPEG standard
The still image data compression standard JPEG (JointPhotographicExpertsGroup), the Joint Photographic Experts Group, is a collaboration between the International Organization for Standardization (ISO), the International Telegraph and Telephone Consultative Committee (CCITT) and the International Electrotechnical Commission (IEC). It was completed in 1991 by. JPEG is both an ISO standard and CCITT's recommended standard. Its goal is to compress still color picture data, which is mostly used in the transmission and storage of satellites and news pictures, as well as graphics and image document data processing.
(4) MPEG standard
With the widespread application of digital audio and digital video technologies, ISO's Moving Picture Expert Group (Moving Picture Expert Group) proposed a draft proposal for the ISOll172 standard in November 1991, commonly known as the MPEG-1 standard, which was passed in November 1992. The MPEG-1 standard is suitable for the application environment where the digital rate is around 1.5Mbps, which is formulated for the video storage and playback of CD-ROM discs.
MPEG-2 is the second standard developed by MPEG, which was formally confirmed as an international standard in November 1994. MPEG-2 is the "Generic Coding of Moving Pictures Associated Audio Information" (Generic Coding of Moving Pictures Associated Audio Information) standard. As a recognized compression scheme, the standard has the advantages of openness, low technical cost, interoperability and flexibility, optional scalability of bit rate, and support from many manufacturers. It has been adopted in the fields of networks, communications, satellites, etc. .
MPEG-4 was formulated in 1993 and was only finalized in October 1998. It was not until the beginning of 2000 that it officially became an international standard. The standard has many compelling functions, including object content-based video object access, scene content-based scalability, video access, and error correction capabilities. The MPEG-4 video standard can not only provide a new type of multimedia information transmission standard with more compression efficiency, but also has good interactivity, all-round memory and tolerance. The origin of its name is 1+2+4= 7 (MPEG-1, MPEG-2, MPEG-4). It extends the limited capabilities of existing content recognition solutions to include more data types. MPEG-7 is a set of standards that specifies a set of descriptors used to describe various types of multimedia information.
2. Digital video compression method
Based on the above-mentioned standards, currently the three compression methods widely used in the television field are MPEG-2, M-JPEG and DV. They are all based on Discrete Cosine Transform (DCT), and run-length coding is performed after minimizing the transform coefficients.
(1) Introduction to JPEG JPEG is used for continuously changing still images, including continuous changes in gray scale and color. JPEG includes two basic compression methods: the first is lossy compression, which is a compression method based on DCT (DiscreteCosineTransform); the second is lossless compression, also known as predictive compression. The most commonly used is the former, the DCT compression method, also known as the Baseline Sequential Codec (Baseline Sequential Codec) method. This method is advanced, effective, simple, and easy to communicate, so it is widely used.
(2) Introduction to M-JPEG
M-JPEG is based on the normal speed of moving images. It compresses each frame in 25 frames of images per second. Each frame is treated as an independent signal. A series of frames is actually one JPEG signal flow. The advantage of this design is that it is easy to edit and can edit any frame randomly, which is an excellent choice for non-linear editing applications. The compression and decompression of M-JPEG are symmetrical and can be realized by the same hardware and software. The disadvantage is that it requires too much bandwidth and storage space. This is because it does not compress on the line, but only compresses within the frame, and the compression efficiency is not high enough.
(3) Introduction to DV
The DV compression method is an expandable format designed for home video recorders, which can be applied to standard definition televisions and high-definition televisions. DV compression was first developed by an alliance of standard and high-definition household VCR manufacturers. DV uses 13.5MHz sampling rate, 4:1:1 encoding, and uses 8-bit codes to improve the signal-to-noise ratio, and its spatial compression ratio is 5:1. DV expands from the standard 25Mb/s to 50Mb/s in DVCPRO50 by advocating this compression for video images that are essentially inactive. Sony provides DVCAM series VTR based on DV compression. There are two main models of DVCPR0 cameras used in broadcast television: one is DVCPR025 and the other is DVCPR050.
(4) Introduction to MPEG
The basic steps of MPEG standard digital compression are: first convert analog video to digital video and then group it in time sequence, select a reference image for each group of pictures (GOP), use motion estimation to reduce the time redundancy between images, and finally combine the reference image Perform discrete cosine transform (DCT), coefficient quantization and entropy coding (VLC&RLC) with motion estimation error to eliminate spatial redundancy. The initial tasks of the MPEG expert group are three: to achieve 1.5Mb/s, 10Mb/s, 40Mb/s compression coding standards, namely MPEG-1, MPEG-2, MPEG-3, of which MPEG-3 was cancelled in 1992 .
The MPEG-l standard is used for moving images and its audio coding standards, focusing on high compression rate, low bandwidth and low resolution, and the video rate is roughly 1.5Mb/s. The basic algorithm is to compress the spatial resolution in the horizontal direction (360 pixels) and the vertical direction (288 pixels), and it has a better effect on moving images with 24 to 30 frames per second. The MPEG-l standard also provides some video recorder functions: forward playback, image freezing, fast forward, fast reverse and slow playback, etc., as well as random storage functions. The MPEG-l standard also uses a series of technologies to obtain a high compression ratio: ①Sub-sampling the color difference signal to reduce the amount of data; ②Using motion compensation technology to reduce line quantization, discarding unimportant information, and quantizing the DCT component Reorder according to frequency; ⑤ the DCT component is coded with variable word length; ⑥ the DC component (DC) of each data block is predicted and differentially coded.
The MPEG-2 standard is similar to the MPEG-1 standard, and its bit rate is much higher than the latter, so it requires a higher bandwidth and resolution. The MPEG-2 standard can define a bit rate of up to 400Gb/s and an image of 16000×16000 pixels. It uses intra-frame coding and quality control. The OP (group of pictures) is divided into I frame (intra-frame coding frame), P frame (forward prediction coding frame), and B frame (bidirectional prediction frame). Compression encoding method. In January 1996, the MPEG-2MP@ML standard with high broadcast quality and high editing accuracy was confirmed at the International Munich Group Conference. It allows a shorter GOP and makes it suitable for precise editing of program production. MPEG-2 can automatically change the compression rate in processing the "simple" and "complex" areas of the image. It can use different compression ratios in the same frame, so it is more effective. Under the condition of compressing to the same image quality, the space occupied by MPEG-2 images is only 10% to 15% of M-JPEG images. MPEG-2 has gradually been widely adopted in various fields such as image acquisition, production, transmission, and broadcasting.
MPEG-4 not only fully supports all the video functions provided by MPEG-1/2, including effective encoding of standard rectangular area image sequences under different input formats, frame rates, and bit rates, but also adds a new function: to improve For transmission efficiency, MPEG-4 uses "sub-graphics" prediction and encoding technology. It takes the static background as "sub-graphics" and sends it to the receiving end first, and stores it in the encoder and decoder as the first frame, and then uses the camera The movement, rotation and zooming of the video object in front of the background are taken, and then encoded separately to form a video sequence for transmission, and then reconstruct the original image. This technology is very beneficial to the realization of multimedia databases, while also improving image quality. MPEG-4 is a highly efficient coding standard, and its minimum bit rate can reach 5~64kbps. For specific videos, its interactivity and operability can be compatible with various encodings in the field of multimedia applications. MPEG-7 is built on the basis of MPEG-4 and uses few features to retrieve information content. For example, for graphics, as long as you draw a few lines, you can find the corresponding graphics, trademarks, etc. that include the feature.
3. Comparison of 3 commonly used digital compression formats
M-JPEG, DV and MPEG are the three main compression technologies in the video industry. They are all based on DCT. The images they record are converted into uniform, quantized and variable-length-encoded frequency domain coefficients. Among them, DV and typical M-JPEG are intra-frame coding, using intra-frame compression methods, without suffocation. For MPEG-2, when using PEG-2 for editing, it is generally limited to I-frame coding, and can switch frames at the edge without knowing the previous frame and the next frame. In addition, DV and MPEG-2 compression use motion adaptive processing to achieve effective intra-frame coding. However, DV can only perform fixed bit rate (CBR) coding, while MPEG-2 and M-JPEG can perform CBR and variable Bit rate (VBR) encoding.
Digital video compression technology enables us to obtain high-quality video at a relatively low cost, and it is possible to spread video signals for high-quality, and with the continuous development of television technology, this technology is still being updated and improved. When TV technology and Internet technology are combined, digital video technology more embodies its advantages in communication and communication.
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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
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1.How far you want to cover in diameter ?
2.How tall of you tower ?
3.Where are you from ?
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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 .
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