Video compression standard
Digital video technology is widely used in communications, computers, broadcast television and other fields, bringing a series of applications such as conference TV, videophone and digital TV, media storage, etc., which has led to the emergence of many video coding standards. The differences and connections between the various compression standards are detailed below.
1, MJPEG (rarely used)
MJPEG: MJPEG refers to MotionJPEG, which is a dynamic JPEG. The video signal is compressed by the JPEG algorithm at a rate of 25 frames per second to complete the compression of the dynamic video. MJPEG is developed by the JPEG expert group. The image format is compressed for each frame, usually up to a compression ratio of 6:1, but this ratio is still relatively insufficient.
The advantage of MJPEG is that the picture quality is still relatively clear. The disadvantage is that the compression ratio is low and the bandwidth is large. Generally, the single channel occupies a bandwidth of about 2M.
In addition, since MJPEG is not a standardized format, each manufacturer has its own version of MJPEG, and the files of both parties cannot recognize each other.
2, MPEG-1
MPEG-1 was once the main compression standard of VCD, and it is also the video compression format widely used by the first generation DVR.
MPEG-1 was developed in 1992 and is designed for industrial standards. It can be used in devices with different bandwidths, such as CD-ROM and Video-CD.
MPEG-1 is used to transmit the moving image of digital storage media with 1.5Mbps data transmission rate and its accompanying audio. After compression by MPEG-1 standard, the video data compression rate is 1/100 - 1/200, the resolution of video and video images. It is 360 × 240 × 30 (manufactured by NTSC) or 360 × 288 × 25 (made by PAL).
3, MPEG-2
MPEG-2 is the designated standard for DVDs. It was established in 1994 and is designed to meet the image quality of advanced industry standards and higher transmission rates.
MPEG-2 is mainly for the needs of high definition television (HDTV), with a transmission rate of 3-10 Mbits/sec, compatible with MPEG-1, and suitable for encoding range of 1.5-60 Mbps or higher. The resolution is 720 × 480 × 30 (manufactured by NTSC) or 720 × 576 × 25 (made by PAL).
MPEG-2 has the best picture quality, but it also consumes a lot of bandwidth. It is not suitable for long-term storage and network transmission between 4M and 15M.
4, MPEG-4
The MPEG-4 video compression standard was finalized in October 1998 and became an international standard in January 1999.
MPEG-4 is a compression standard for ultra-low bit rate moving pictures and languages, which combines the advantages of MPEG-1 and MPEG-4. Its transmission rate requirements are lower, between 4800 and 64000 bits/sec with a resolution of 176X144.
MPEG-4 utilizes a very narrow bandwidth to compress and transmit data through frame reconstruction techniques to achieve optimal image quality with minimal data. The occupied bandwidth of the MPEG-4 standard is adjustable, and the occupied bandwidth is proportional to the sharpness of the image.
5, H.263
H.263 is a draft standard for the ITU ITU-T and is a low bit rate image compression standard designed for medium and high quality moving image compression.
The H.263 standard has a high compression ratio. In the full real-time mode of the CIF format, the single-channel occupied bandwidth is generally in the range of several hundred or so. The specific occupied bandwidth varies depending on the amount of motion of the picture. The disadvantage is that the picture quality is relatively poor, and the occupied bandwidth varies greatly with the complexity of the picture motion.
6, H.264
The H.264 standard is a digital video coding standard proposed by the joint video group (JVT, JointVideoTeam) jointly developed by ITU-T's VCEG (Video Coding Experts Group) and ISO/IEC MPEG (Moving Picture Experts Group), which is both ITU- T's H.264 is the 10th part of the ISO/IEC MPEG-4 standard (also known as AVC, or "Advanced Video Coding" or "Advanced Video Coding").
Under the same image quality, H.264 saves about 50% of the code rate than H.263, and saves 64% of the transmission code stream compared with the previous generation coding standard MPEG2, and saves 39% of the transmission code on average compared to MPEG4 (ASP). flow.
Due to its higher compression ratio, better IP and wireless network channel adaptability, it is more and more widely used in digital video communication and storage. At the same time, it should be noted that the cost of obtaining superior performance of H.264 is an increase in computational complexity. It is estimated that the computational complexity of coding is approximately three times that of H.263, and the decoding complexity is approximately twice that of H.263.
The H.264 standard is divided into three profiles: Baseline, Main, and High, which represent algorithm sets and technical limitations for different applications.
Baselineprofile: A simple version of H.264 that includes technical features such as low complexity, low latency, and fault tolerant lines, primarily for interactive applications.
Mainprofile: The main framework of H.264 uses a number of technical measures to improve image quality and increase compression ratio, which can be used for SDTV, HDTV and DVD.
Highprofile: Mainly for streaming applications, all fault-tolerant technologies and flexible access and switching technologies for bitstreams will be included in this framework.
At present, the domestic industry commonly referred to as MPEG-4 refers to the second part of MPEG-4 (ISO14496-2, also known as SP/ASP), including 3ivx, DivX4/ProjectMayo, DivX5, Envivio, ffmpeg/ffds, mpegable, Common video formats such as NeroDigital, QuickTime, Sorenson, XviD.
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