The MPEG standard is formulated by mpeg-1| mpeg-2 | (mpeg-3) | mpeg-4 | mpeg-7 | mpeg-21
ITU-T standard is formulated by VCEG H.261| (H.262) | H.263 | H.263V2 | H.264.
MPEG-2 is an international standard for video and audio compression published by MPEG Working Group in 1994. MPEG-2 is usually used to provide video and audio coding for broadcast signals, including digital satellite tv and cable TV. After several modifications, MPEG-2 has become the core technology of DVD products.
The system description part (1 part) of MPEG-2 defines the transport stream as a mechanism for transmitting digital video signals and audio signals on unreliable media, which is mainly used in the field of radio and television.
The second part of MPEG-2, the video part, is similar to MPEG- 1, but provides support for interlaced video display mode (interlaced scanning is widely used in the field of broadcasting and television). MPEG-2 video is not optimized for low bit rate (less than 1Mbps), and it is obviously superior to MPEG- 1 at the bit rate of 3Mbit/s and above. MPEG-2 is backward compatible, that is, all MPEG-2 decoders that meet the standards can also play MPEG- 1 video streams normally.
MPEG-2 technology is also applied to HDTV transmission system.
The third part of MPEG-2 defines the audio compression standard. This part improves the audio compression of MPEG- 1 and supports more than two audio channels. MPEG-2 audio compression also maintains backward compatibility.
The seventh part of MPEG-2 defines audio compression that is not backward compatible. This part provides a stronger audio function. Usually, what we call MPEG-2AAC refers to this part.
MPEG-2 video usually contains multiple GOP(GOP = picture group), and each GOP contains multiple frames. Frame types of frames usually include I frame, P frame and B frame. Among them, I frame adopts intra coding, P frame adopts forward estimation and B frame adopts bidirectional estimation.
Generally speaking, the input video format is 25(CCIR standard) or 29.97 (FCC) frames per second.
MPEG-2 supports interlaced scanning and progressive scanning. In progressive scanning mode, the basic unit of coding is frame. In interlaced scanning mode, the basic coding can be one frame or one field.
The original input image is first converted to YCbCr color space. Where y is brightness and Cb and Cr are two chroma channels. For each channel, block division is used first, and then "macro block" is formed, which constitutes the basic unit of coding. Each macroblock is subdivided into 8×8 small blocks. The number of smaller blocks of the chroma channel depends on the initial parameter setting. For example, in the commonly used 4:2:0 format, each chroma macroblock only samples one small block, so the number of small blocks that three channel macroblocks can be divided into is 4+ 1+ 1=6.
For I frame, the whole image directly enters the coding process. For P and B frames, motion compensation should be done first. Generally speaking, because of the strong correlation between adjacent frames, macroblocks can find similar areas in the corresponding similar positions in the previous frame and the next frame. This offset is recorded as a motion vector, and the error of the reconstructed area of motion estimation is sent to the encoder for encoding.
For each 8×8 block, the discrete cosine transform transforms the image from the spatial domain to the frequency domain. The obtained transform coefficients are quantized and rearranged, thus increasing the possibility of long zeros. And then run-length coding. Finally, huffman encoding.
I-frame coding is to reduce spatial redundancy, and P-frame and B-frame are to reduce temporal redundancy.
The GOP consists of a series of I-frames, P-frames and B-frames with fixed patterns. The commonly used structure consists of 15 frames, and the format is as follows: IBBPBBPBBPBBPBB. The selection of frame ratio in GOP is related to bandwidth and image quality requirements. For example, because the compression time of B frames may be three times that of I frames, it may be necessary to reduce the proportion of B frames for some real-time systems with weak computing power.
The bitstream output by MPEG-2 can be uniform or variable. For example, in DVD application, the maximum bit rate can reach10.4 mbit/s. If you want to use a fixed bit rate, you need to constantly adjust the quantization scale to produce a uniform bit stream. However, increasing the quantization scale may bring visual distortion. Such as mosaic phenomenon.
[Edit] MPEG-2 Audio Coding
Audio coding of MPEG-2 includes:
MPEG- 1 layer 1/2/3LSF low bit rate.
Multichannel coding
MPEG-2 AAC .
[Editor] The Application of MPEG-2 in DVD
DVD adopts MPEG-2 standard and introduces the following technical parameter restrictions:
resolution ratio
720x480,704x480,352x480,352x240 pixels (NTSC standard)
720x576,704x576,352x576,352x288 pixels (PAL system)
aspect ratio
4:3
16:9
Frame rate (frame playback speed)
59.94 fields/sec, 23.976 frames/sec, 29.97 frames/sec (NTSC)
50 fields per second, 25 frames per second (PAL)
Video+audio bit rate
The average maximum buffer is 9.8 megabits per second.
Peak value15mbit/s
Minimum 300 kilobits/second
YUV 4:2:0
Subtitle support
Embedded subtitle support (NTSC only)
audio frequency
LPCM code: 48 kHz or 96 kHz; ; 16 or 24; ; Up to 6 channels
MPEG Layer 2 (MP2): 48 kHz, with a maximum of 5. 1 channel.
Dolby digital-dolby digital (DD, also known as AC-3): 48kHz, 32-448 kbit/s, with a maximum of 5. 1 channel.
Digital Home Cinema System-Digital Cinema System (DTS): 754 kbit/s or1510 kbit/s.
NTSC DVD must contain at least one LPCM or dolby digital.
PAL DVD must contain at least one MPEG Layer 2, LPCM or dolby digital.
GOP structure
The header information of the sequence must be provided to the GOP.
A GOP can contain maximum number of frames: 18 (NTSC)/ 15 (PAL).
[Edit] Application of MPEG-2 in DVB
Technical parameters related to DVB-MPEG:
One of the following resolutions must be met:
720 × 480 pixels, 24/ 1.00 1, 24,30/1.001or 30 frames per second.
640 × 480 pixels, 24/ 1.00 1, 24,30/1.001or 30 frames per second.
544 × 480 pixels, 24/ 1.00 1, 24,30/1.001or 30 frames per second.
480 × 480 pixels, 24/ 1.00 1, 24,30/1.001or 30 frames per second.
352 × 480 pixels, 24/ 1.00 1, 24,30/1.001or 30 frames per second.
352 × 240 pixels, 24/ 1.00 1, 24,30/1.001or 30 frames per second.
720 × 576 pixels, 25 frames per second
544 × 576 pixels, 25 frames per second
480 × 576 pixels, 25 frames per second
352 × 576 pixels, 25 frames per second
352 × 288 pixels, 25 frames per second
[edit] MPEG-2 and ATSC
One of the following resolutions must be met:
1920 × 1080 pixels, with a maximum of 60 frames per second (1080i).
1280 × 720 pixels, with a maximum of 60 frames per second (720p).
720 × 576pixels, with a maximum of 50 frames per second and 25 frames per second (576i, 576 p).
720 × 480 pixels, with a maximum of 60 frames per second and 30 frames per second (480i, 480p).
640 × 480 pixels, with a maximum of 60 frames per second.
Note: 1080i is encoded with 1920× 1088 pixels, but the last 8 lines are discarded when displayed.
[Edit] MPEG-2 standard file number
Iso/iec13818-1:system-describes the synchronization and multiplexing technology of video and audio.
ISO/IEC 138 18-2: video-video compression
ISO/IEC 138 18-3: audio-audio compression, including multi-channel MP3 expansion.
ISO/IEC 138 18-4: test specification
ISO/IEC 138 18-5: simulation software.
Iso/iec13818-6: DSM-cc (digital storage media command and control) extension.
ISO/IEC 138 18-7: advanced audio coding (AAC)
ISO/IEC 138 18-9: real-time interface extension
Iso/iec13818-10: DSM-cc specification.
[Editor] Patent holder
The core technology of MPEG-2 involves about 640 patents.
These patents are mainly concentrated in 20 companies and one university
Headquartered in France
General regulations
Columbia University
France Telecom (CNET)
Fujitsu Corporation of Japan
General electric capital company
General instrument company
General electric technology development company.
Hitachi
KDDI
Lucent technology
lg electronics
Panasonic
mitsubishi
Japan Telecom Telephone Company (NTT)
Philips
Robert bosch ltd.
Orion belt
Sanyo electrics
Scientific Atlanta
sharp
Sony
Thomson Licensing Ltd.
Toshiba
Victor Company of Japan, Limited
[Edit] See
MPEG-2 authorization
MPEG- 1
MPEG-4
H.26 1
263
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