Category: Embedded
Compression is the core technology network video servers and network cameras, compression largely determines the quality of the image compression ratio, transmission efficiency, transmission speed and other properties, it is important to evaluate the merits of a network video server and network camera performance a ring.
With the development of multimedia technology, have launched a number of compression coding standard, currently there are JPEG / M-JPEG, H.261 / H.263 and MPEG standards.
. 1, the JPEG / M the JPEG-
①, the JPEG standard for still image compression, which is a standard frame compression encoding.
When the hardware processing speed is fast enough, JPEG can be used for real-time moving video image compression.
In the case where small variation of a screen can provide very good image quality, transmission speed, quite safe to use, the disadvantage is a large amount of data.
②, M-JPEG from JPEG compression technique, it is a simple frame JPEG compression, the compressed image quality is better, in no mosaic screen changes, but due to this compression technique itself is limited, can not do a large compression ratio per hour about 1-2GB space, you need time video network transmission 2M bandwidth, whether video or send a transmission network, will spend a lot of hard disk capacity and bandwidth, not suitable for long continuous recording needs, not practical in video network transmission image.
2, the H.261 / H.263
①, the H.261 standard is generally referred to as P * 64, H.261 for full color, real-time transmission of moving images can achieve a higher compression ratio, before and after the algorithm applied by the inter-frame compression compression coding combination, to provide fast video compression and decompression process.
Since the inter-frame compression algorithm after only one to predict, so the duration of comparative advantage, but the image quality is difficult to achieve high resolution, can not achieve large compression ratio and variable rate videos.
②, the basic encoding method H.263 H.261 is the same, are hybrid coding method, but to adapt the transmission H.263 low bit-rate, has been improved in all aspects of encoding, such as provincial code word to improve the quality of coded images, in addition, also draws H.263 MPEG bidirectional motion prediction of other measures to further improve the prediction accuracy of inter-coding, generally, at low bit rate, as long as half the rate using H.263 availability and H.261 equivalent image quality.
. 3, the MPEG
the MPEG standard compression is audio coding of moving pictures and associated audio, which uses the interframe compression, where only the difference between successive frames is stored, so as to achieve higher compression ratio.
MPEG conventional MPEG? 1, MPEG? 2 and MPEG?. 4 three versions, to adapt to different requirements of bandwidth and image quality.
①, MPEG? 1 video compression algorithms rely on two basic techniques, one based on 16 * 16 (pixels * lines) of the motion compensation block, the second is based on transform domain compression techniques to reduce spatial redundancy . 4 dated 30 day Sunday clear , the compression ratio is higher compared to M-JPEG, motion video signal is not fierce obtain better image quality, but intense exercise, will produce an image mosaic.
MPEG-1 data rate transmission of video and audio signals to 1.5Mbps, MPEG-1 corresponds to the quality of VHS video image in the video image quality, the quality of the color pattern definition video recording ≥240TVL, the two stereo sound near CD sound quality.
MPEG-1 is the front and rear frame multi-frame prediction compression algorithm, compression has great flexibility to variable rate compressed video, video of different visual environments, different compression quality settings, ranging from 400MB to 80MB per hour, but the amount of data and bandwidth is quite large.
②, MPEG-2 which is a higher resolution (720 * 572) providing a video and audio coding standard broadcast quality.
MPEG-2 compatible extension as MPEG-1, which supports a number of advanced features and video formats interlaced comprises adjustable support multiple levels of video encoding, such as multiple rates for a variety of quality and resolution of a variety of situations.
It is suitable for a large change in motion, demanding image quality of real-time image.
30 frames per second, 720 * 572 resolution video signal compression, data rates up to 3-10Mbps.
Since the data is too big, not suitable for long continuous recording needs.
③, MPEG-4 is designed for low speed mobile communication device real-time transmission in the Internet network and the development of video and audio signals, a high compression ratio of video and audio coding standard.
MPEG-4 compression standard object-oriented manner, not like MPEG-1 and MPEG-2 as simply an image is divided into a number of image blocks, but by the content of the image, wherein objects (object, person, background) isolated , respectively, intra-inter coding and allows flexible allocation rate between different objects a drop diary ! ~ .20. , more important object allocation bytes, compared to the secondary object allocation fewer bytes, thus greatly improving the compression ratio, to obtain better results at a lower rate, taught in adversity , MPEG-4 supports MPEG-1, MPEG-2 in most of the functions provided different video efficient encoding standard source format, bit rate, frame frequency rectangular pattern images.
In short, MPEG-4 advantage three aspects:
①, has good compatibility;
②, MPEG-4 offers better compression ratio than other algorithms, up to 200: 1;
③, MPEG-4 at the same time provide a high compression ratio, data loss is small.
Therefore, the application of the MPEG-4 video can greatly reduce the storage capacity, a high resolution recording is obtained, particularly suitable for the needs of real time video, along with excellent in low-bandwidth network transmission capacity.
4, H.264 is the ITU-T VCEG (Video Coding Experts Group) and ISO / IEC MPEG (Moving Picture Coding Experts Group) Joint Video Team (JVT: joint video team) a new digital video coding standard developed by , it is both the ITU-T H.264, but also a part 10 ISO / IEC MPEG-4 of the.
January 1998 began the draft solicitation, in September 1999, to complete the first draft, the last fishermen's paradise 3 , 2001, to develop its test mode TML-8, through June 2002, the 5th meeting of the JVT the FCD board of H.264.
At present, the standards are still under development, the first half of next year is expected to be formally adopted.
H.264 standard, like before, is added to transform hybrid DPCM coding mode.
But it is a "back to basics" simplicity of design, not many options, get much better compression performance than H.263 ++; strengthening the ability to adapt to a variety of channels, a "network-friendly" structure and syntax, facilitate processing of the error and packet loss; target range wider application, to meet the different rates, different resolutions and different transmission requirements (storage) of the case; the basic system is open, without the use of the copyright.
Technically, H.264 standard, a plurality of the flash, as a unified symbol VLC coding, high-precision, multi-mode displacement estimates, based on the integer 4 × 4 block transform, layered coding syntax like.
These measures make H.264 algorithm has a very high coding efficiency, in the same reconstructed image quality, bit rate of about 50% can be saved than H.263.
H.264 bit stream structure of the network adaptability, increased error resilience can be well adapted to IP and wireless network applications, vehicle maintenance .
In fact, most of what H.264 is H.263 ++ by the improved algorithm, the compression ratio becomes smaller points! If the comparison is clarity from a single screen, MPEG4 has an advantage; from the definition of continuity of action, H.264 advantage!
