Video coding technology

MJPEG, MPEG 1/2, MPEG-4 (SP/ASP), H.264/AVC, VC- 1, RealVideo and other video coding technologies. Mainly used for monitoring. For the end user, his main concerns are: clarity, storage capacity (bandwidth), stability and price. Using different compression technologies will greatly affect the above factors.

MJPEG

MJPEG (moving JPEG) compression technology is mainly based on static video compression. Its main feature is that it basically does not consider the changes between different frames in the video stream, and only compresses a certain frame.

MJPEG compression technology can obtain high-definition video images and dynamically adjust the frame rate and resolution. However, because the changes between frames are not taken into account and a lot of redundant information is repeatedly stored, a single-frame video takes up a lot of space, and the best monitoring and video coding of popular MJPEG technology can only achieve 3 kilobytes per frame, usually 8 ~ 20 kilobytes!

MPEG- 1/2

The MPEG- 1 standard mainly aims at the resolution of SIF standard (NTSC standard is 352X240；; PAL system is 352X288). The main target of compression bit rate is1.5mb/s/s. Compared with MJPEG technology, MPEG 1 has a significant improvement in real-time compression, data volume per frame and processing speed. However, MPEG 1 also has many shortcomings: the storage capacity is still too large, the definition is not high enough, and the network transmission is difficult.

MPEG-2 has been expanded and upgraded on the basis of MPEG- 1, and the backward compatibility of MPEG- 1 is mainly used in storage media, digital TV, high definition and other application fields. The resolutions are: low resolution (352x288), medium resolution (720x480) and the second highest resolution (1440x65438). Compared with MPEG- 1, MPEG-2 video improves the resolution and meets the user's requirements for high definition. However, due to the little improvement of compression performance, the storage capacity is still too large, which is not suitable for network transmission.

MPEG-4

Compared with MPEG- 1/2, MPEG-4 video compression algorithm has a significant improvement in low bit rate compression. In the case of CIF(352*288) or higher definition (768*576), video compression has greater advantages than MPEG- 1 in definition and storage capacity, and is more suitable for network transmission. In addition, MPEG-4 can dynamically adjust the frame rate and bit rate conveniently to reduce the storage capacity.

Because the system design of MPEG-4 is too complicated, it is difficult for MPEG-4 to be fully compatible, and it is also difficult to be realized in video conferencing, videophone and other fields, which deviates from the original intention. In addition, Chinese enterprises are also facing the problem of high patent fees, which stipulates:

-Each decoding device needs to pay MPEG-LA 0.25.

-codec equipment also needs to be paid by time (4 cents/day = 1.2 USD/month = 14.4 USD/year).

H.264/AVC

The international standards of video compression mainly include H.26 1, H.262, H.263 and H.264 formulated by ITU-T and MPEG- 1, MPEG-2 and MPEG-4 formulated by MPEG, among which H.262/MPEG-2 and H.264/MPEG-4 AVC are made by.

Simply put, H.264 is a video coding technology, which belongs to the same technology as WMV9 of Microsoft, that is, the "encoding and decoding" program for compressing dynamic image data.

Generally speaking, if dynamic image data is used without compression, the amount of data is very large, which is easy to cause communication line failure and insufficient data storage capacity. Therefore, it is necessary to use codec when sending dynamic images, or saving image content on DVD, or shooting images with a digital camera or camera phone with small storage medium capacity. Although there are many kinds of codecs, MPEG-2 is mainly used for DVD video and microwave digital TV, while MPEG-4 is mainly used for digital cameras.

As a compressed video coding technology, H.264 plays the most important role in video compression. The familiar MPEG2-2, the most commonly used DVD video coding technology, has fallen behind.

For the most wanted HDTV program, if the broadcast time is about 2 hours, it can only be compressed to 30GB by using MPEG2-2, but it can be compressed to less than 15GB by using high compression rate codecs such as H.264 and WMV9-9, and the image quality is not degraded.

The above example illustrates the technical advantages of H.264. Generally speaking, the data compression rate of H.264 is more than twice that of MPEG2 and 1.5 times that of MPEG4. Theoretically, under the same picture quality and capacity, it can save images for more than 2 times longer than DVD discs. Codecs are widely used as video content, such as movies and concerts, and portable devices.

Everyone still remembers the video decompression card, that is, DVD/VCD decompression card. The principle of this thing is very simple, that is, the DSP chip is installed on the card, and the only function of this chip is to decompress the code with special format. When the performance of the graphics card is gradually enhanced to meet the demand of video playback, the video decompression card disappears.

ATI's approach is that the latest R520 VPU includes H.264 decoding technology. This special algorithm is directly handed over to the graphics card VPU for operation, instead of being completely handed over to the CPU, so that the CPU can free up its hands for more complicated operations.

H.264 concentrates the advantages of previous standards, and has made breakthrough progress in many fields, which makes it obtain much better overall performance than previous standards:

-Compared with H.263+ and MPEG-4 SP, it can save up to 50% code rate and greatly reduce the storage capacity;

H.264 can provide high video quality at different resolutions and different bit rates.

-Adopt a "network-friendly" structure and grammar to make it more conducive to network transmission.

With simple design, H.264 is easier to popularize than MPEG-4, easier to implement in video conference and videophone, easier to realize interconnection, and can be easily combined with low bit rate speech compression such as G.729 to form a complete system.

MPEG LA has absorbed the high patent fee of MPEG-4, so it is difficult to popularize it. MPEG LA has formulated the following low-cost charging standards for H.264: H.264 basically does not charge when playing; When the H.264 codec is embedded in the product, the annual output is less than 654.38+10,000 units, 0.2 USD for more than 654.38+10,000 units and 0. 1 USD for more than 5 million units. Low patent fees make it easier for China H.264 monitoring products to go global.

H.264 development history

With the evolution of NGN, 3G and 3G, and NGBW's rapid demand for video, multimedia services and network applications, efficient video digital compression coding technology, as the core technology of video services and storage applications, has attracted more and more attention and become a bright spot and hot spot in the fields of broadcasting, video and multimedia communication, among which H.264 video coding standard is a household name.

As early as 1993, ITU-T (Telecommunications Standardization Department of International Telecommunication Union) formulated the first video coding standard H.26 1, with an output rate of p*64 kbit/s, which is mainly used for quasi-broadband and broadband channel videos such as ISDN and ATM. With the continuous development of time, it experienced H.263 in 1996, H.263+ in 1998 and H.263++ in 2000. By 200 1 year, MPEG realized the potential advantages of H.264/AVC and the necessity of cooperation with VCEG, so the cooperation between them was established. This standard is called H.264 in ITU-T; In ISO/IEC, it is called MPEG-4-Part 10 AVC (Advanced Video Coding, Part10), which is what we are all talking about today.

Compared with some previous coding standards, H.264 standard inherits the advantages of H.263 and MPEG 1/2/4 video standard protocols, but the structure has not changed, only some advanced technologies are adopted in each main functional module, which improves the coding efficiency. Its main performance is that the coding is no longer based on 8×8 blocks, but on 4×4 blocks for residual transformation coding. The adopted transform coding method is no longer DCT transform, but integer transform coding. The context adaptive binary arithmetic coding (CABAC) with higher coding efficiency is also different from the corresponding quantization process. H.264 standard is a more practical and effective image coding standard, which has the advantages of simplicity, easy realization, high accuracy without overflow, fast operation speed, small memory occupation and weakening block effect.

Compared with H.263/MPEG-4, H.264/AVC has greatly improved its compression coding efficiency, adaptive processing ability of video content and network level, especially its adaptive processing ability, anti-interference ability and robustness to IP network and mobile network, which also caused H.264 to be heated up. It should be said that H.264/AVC is widely used, including fixed or mobile videophone, mobile phone, real-time video conference, video monitoring, streaming media, multimedia video, Internet video and multimedia, IPTV, mobile TV, broadband phone and video information storage. This is also an important reason why the industry generally values it.