compression and network video server, network camera's core technology, compression to a large extent determines the image quality, compression ratio, transmission efficiency and transmission speed and other properties, it is to evaluate network performance, network cameras and video servers merits an important part.
With the development of multimedia technology, has introduced a number of compression standards, currently there are JPEG / M-JPEG, H.261/H.263 and MPEG standards.
1, JPEG / M-JPEG
①, JPEG is a compression standard for still images, it is a standard intra-frame compression encoding.
When the hardware processing speed fast enough, JPEG can be used for real-time moving images of video compression.
In the case of small changes in the screen can provide very good image quality, transmission speed, the use is safe,[url=http://www.uggclearancemall.com/][b]title=UGG Boots Clearance[/b][/url], drawback is large amount of data.
②, M-JPEG from the JPEG compression technology, is a simple frame JPEG compression, image quality is better, the screen changes in the case of non-mosaic, but due to technical limitations of this compression itself, can not do large proportion of compressed video is about 1-2GB of space per hour, network transmission, need 2M bandwidth, so either send video or network transmission, will spend a lot of hard disk capacity and bandwidth, not suitable for long continuous recording of demand, not useful in network transmission of video images.
2, H.261/H.263
①, H.261 standard is usually referred to as P * 64, H.261 for full-color, real-time transmission of moving images can achieve a higher compression ratio, the algorithm from the frame within the frames before and after compression plus a combination of compression, video compression and decompression in order to provide fast processing. As the inter-frame compression algorithms
only after a forecast, so in the extension of time has an advantage, but difficult to achieve high image quality clarity, can not achieve large compression ratio and variable-rate videos.
②, H.263 and H.261 basic encoding method is the same, are hybrid coding method, but to adapt to very low bit rate H.263 transmission on all aspects of the code has been improved, such as code word in order to save the image to improve the quality of coding, in addition, H.263 also learn the way of MPEG motion estimation and other measures to further improve the inter-frame prediction accuracy, the general said, in low bit rate, the use of H.263 as long as half the rate of access to and H.261 equivalent image quality.
3, MPEG
MPEG is the compression of moving pictures and audio of the video and audio coding standard, which uses inter-frame compression, only the difference between consecutive frames stored in the place, thus to achieve greater compression ratio.
MPEG existing MPEG-1, MPEG-2 and MPEG-4 three versions to accommodate different bandwidth and image quality requirements.
①, MPEG-1 video compression algorithms rely on two basic techniques, one based on 16 * 16 (pixel * line) block motion compensation, the second is based on transform domain compression techniques to reduce spatial redundancy, M-JPEG compression ratio is higher than for non-violent movement of the video signal can achieve better image quality, but intense exercise,[url=http://www.uggbootsclearanceuks.co.uk/][b]title=UGG Boots UK[/b][/url], the image will have a mosaic.
MPEG-1 to 1.5Mbps data rate transmission of video and audio signals, MPEG-1 video image quality is equivalent to VHS video recorder image quality, clarity, color video mode ≥ 240TVL, two near-CD quality stereo sound of the voice quality.
MPEG-1 is a front and rear frame multi-frame prediction of the compression algorithm, compression has great flexibility to change rate of compressed video, visual recording of different environments, different compression quality settings, ranging from 400MB to 80MB per hour, but the data volume and bandwidth is quite large.
②, MPEG-2 is a higher resolution (720 * 572) to provide broadcast quality video and audio encoding standards.
MPEG-2 as a compatible extension of MPEG-1, which supports interlaced video formats and many advanced features including support for multi-level adjustable video coding for a variety of quality, such as a variety of rates and multiple resolutions of the occasion.
it applies to changes in motion and requires a very high image quality, real-time image.
of 30 frames per second, 720 * 572 resolution video signal compression, data rate of up to 3-10Mbps.
because the data is too big, not suitable for long continuous recording needs.
③, MPEG-4 for mobile communications equipment in the Internet network real-time transmission of video and audio signals and the development of low-rate, high compression ratio of video and audio encoding standards.
MPEG-4 compression standard is object-oriented way, not like MPEG-1 and MPEG-2 as simple as the image is divided into a number of blocks , but according to the image content, in which objects (objects, characters, background) separated, respectively, intra-, inter-frame coding, and allows flexibility in the allocation between the different rate of the object, the object of distribution are more important of bytes allocated to the secondary object less bytes, thus greatly improving the compression ratio, at a lower bit rate to obtain better results, MPEG-4 support for MPEG-1, MPEG-2 in most function, provide different video standard source format,[url=http://www.uggonlineoutlet.us/][b]title=UGG Sale[/b][/url], bit rate, frame rate effectively a rectangular graphic image coding.
In short, MPEG-4 has three advantages:
①, has good compatibility;
②, MPEG-4 than the other algorithms to provide better compression ratio up to 200:1;
③, MPEG-4 provides high compression ratio in the same time, data loss is very small.
Therefore, MPEG-4 applications can significantly reduce video storage capacity, higher video resolution, especially for long time recording needs, along with excellent low bandwidth network transmission capacity.
4, H.264 is the ITU-T VCEG (Video Coding Experts Group) and the ISO / IEC MPEG (Moving Picture Coding Experts Group) Joint Video Team (JVT: joint video team) developed a The new digital video coding standard, it is both the ITU-T H.264, but also the ISO / IEC MPEG-4 Part 10.
1998 draft collection start in January, September 1999, completed the first draft, May 2001, developed its test model TML-8, 2002 June 5 JVT meeting adopted the H.264 FCD board.
Currently the standard is still under development, is expected to be formally adopted by the first half of next year.
H.264 and previous standards, but also increases transform coding DPCM hybrid coding mode.
but it is a ability to adapt to the channel, the use of The basic system is open, use without copyright.
technically, H.264 standard in more than one flash of the Department, such as unified VLC symbol coding, high-precision, multi-mode displacement is estimated, based on the 4 × 4 integer transform blocks, such as layered coding syntax. These measures make
H.264 algorithm has a very high coding efficiency, in the same reconstructed image quality, the ability to save 50% than the H.263 bit rate.
H.264 bit stream structure of the network adaptability, increased error resilience can adapt well to the application of IP and wireless networks. In fact, most of what
H.264 are H.263 + + by the improved algorithm, the compression ratio becomes smaller point! If the definition is more from a single screen, MPEG4 has an advantage; continuity from the action on the resolution, H.264 has an advantage!
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