Standard video and audio compression technology is a brief description audio business flow characteristics,not very compressed video data transmission on the Internet results can not be tolerated.it will easily be engulfed network resources, resulting in network congestion or even collapse.Thus, IP Video Communication is the first video compression.Video Coding theory is based on information theory.Compression is from the time domain, both airspace to remove redundant information can be extrapolated to the identifying information removed soon.Coding method can be broadly divided into three categories :

 1. Taking into account the statistical characteristics of the source image coding method forecast,transform coding, vector quantization coding method subband-codec encoding method and neural networks;

2. Taking into account the visual characteristics of the filter based on the direction of the image coding method,profile based on image / texture coding method;

3. Taking into account the scenery image transmission characteristics of the fractal coding.Module - based coding methods.

IP communication applications in the audio coding method to take into account not only the choice of compression ratio, signal-to-noise ratio.also need to take into account the complexity of the algorithm.The coding algorithm may be too complex a higher compression ratio, but it has also brought greater calculating expenses,Software will affect the real-time communications.Currently, many video coding algorithm,surrounded by the most widely used algorithm is ISO/IEC MPEG and ITU H.26x standards.A.1, A.1.1 MPEG-1 MPEG Standard ISO's Moving Picture Expert Group (MPEG) in the November 1991 draft standards ISO/IEC II 172.commonly known as MPEG-1 standard.The standards adopted in November 1992, published in August 1993.It is designed for industrial-class standards applicable to different bandwidth equipment, such as CD-ROMsVideo-CD, CD-I other.4-5Mbits/s up to a maximum rate of MPEG-1 encoding.A.1.2 introduction of the MPEG-2 MPEG-2 1995 (ISO/IEC Businesses)CCIR601 it is the pursuit of the image quality, namely, DVB.HDTV and DVD images and other developed 3Mbps-10Mbps campaign Audio Coding standard.The resolution is in the NTSC MPEG-2-720  486.MPEG-level video and radio can provide the level of CD sound quality.MPEG-2 audio coding can be provided around the track and the two were around, and a heavy bass track.and as many as seven-channel Audio (DVD dubbing of the reasons may have eight languages).Meanwhile, due to the excellent performance of MPEG-2, have been able to apply to HDTV.MPEG-3 design originally intended for HDTV, even the sky was abandoned.For end users, because television resolution limitabout the high-definition picture quality of MPEG-2 (DVD picture) effects are not obvious on television.Instead, its audio characteristics (such as heavy bass, multi-channel Audio) more and more attention.A.1.3 definition MPEG MPEG Group, following the success of the MPEG-1 and MPEG-2,

in 1994 began a new MPEG-4 (IOS/IEC 14496) standards.MPEG-4 will be a large number of multimedia applications in a complete integrated framework,designed to provide multimedia communication and application of environmental standards and the algorithm toolfor the realization of audio and video (audio-visual) and effective coding data access and more flexible.Trying to achieve two goals : First, MPEG-4 low bit rate multimedia communication;The second is more integrated multimedia communications industry.Accordingly, the introduction of MPEG-4 AV (Audio/Visaul Objects) targetand more interactive operation possible.Much better than MPEG-4 video format : MPEG-1 and MPEG-2 video quality and high resolution.and the data rate is relatively low.The main reason for the use of MPEG-ACE (Advanced decoding efficiency) technology,It is a set of rules used for the first time in the MPEG-4 coding operations.ACE can be opened with the goal orientation of the low data rate.This can be the entire film in a completely PAL or NTSC video with a resolution stereo (16.48 kHz) stored in a single CD-ROM.Specifically : 700 MB capacity for the majority of the 110-minute movies plentiful.and MPEG-2 movies in the format required under the same resolution is about 11 times more storage space.When the data rate of MPEG-2 to almost double the real characteristics,MPEG-4 audio and video streams in a wide range of fields and upgrading.When the video Mbit/s between five and 10 Kbit/s changes,Audio signals can be handled between the two Kbit/s Kbit/s with 24.This can be upgraded, and audio and video data can be specially adjusted to adapt to the real environment.In addition, due to both MPEG-1 and MPEG-2 standard and high standard of the media said.its interactive and less flexibility.The computer network with the flexibility and high degree of interaction, but it has to follow the standard are not compatible with the MPEG standard.MPEG-4 for the effective integration of the three networks.MPEG-4 is an important concept in video object (VO).An image is separated into many arbitrary code when the VO, VO conducted on each of intra-and interframe coding.VO certain only when necessary transmission, greatly improving the efficiency of transmission.If no video segmentation, coding standard rectangular structure only on the level of degradation.This approach MPEG-1/MPEG-2 with similar standards,MPEG-1/MPEG-2 and thereby achieve compatibility.MPEG-4 5-64kbps the lowest rate can be achieved.In the development of low bit rate coding at the same time, focus on specific targets interactive video and operable,encoding for a variety of multimedia application compatibility.MPEG-4 is the first to enable users to be at the receiving end of the images and interactive coding standard for operating.Because based on MPEG-4 audio and video objects (AVO) coding.Object code must also transmit information on the organizational structure dates "scene description," it is not AVO feature,AVO scene said only the structure of space-time relations between objects."Scene description" independent information is transmitted, decoded in the decoder can change the selected AVO "scene description" parameters,The images and voices of the editorial content and operation.For example : additions and deletions to a certain target, a change in the tone of audio and video objects and activate classification coding information.end without any code changes.The introduction of synthetic and natural hybrid of MPEG-4 encoding (Synthetic and Natural Hybrid Coding NHC).Synthesis of this coding will not only greatly improve the coding efficiency (given the low rate 1kbps)Virtual video conferencing systems can be used to enrich the user interaction with the scene.MPEG-4 provides a content-based (object) of random access mode.In the limited time available, the higher the resolution, frames or objects of arbitrary shape,to a random access audio and video sequence.

For example, a sequence of the target object of a certain audio and video into fast search.MPEG-4 coding system is open to various algorithms.Decoders are programmable, and various tools decoder can be downloaded together with the content itself.Types of multimedia applications to provide a flexible and open framework coding tools,MPEG-4 is not only different applications can be selected to meet the needs of multimedia applications on the Internet, real-time multimedia monitorLow Bit-rate mobile multimedia communications, multi-media content storage and retrieval system.applications such as video streaming on the Internet will surely have a far-reaching impact.A.2 H.261 and H.263 H.261 coding frame is a projected decrease in time-domain redundancy,Transform Coding airspace to reduce redundancy hybrid coding method has higher compression ratio, the advantages of low complexity of the algorithm,be more widely used.Mbone important tool is one of the IVS Video Coding H.261 coding algorithm.In H.261 based on the 1996 launch of the ITU-T H.263 coding standard.H.263 to H.261 in many aspects, an improved and expandedCoding little increase in the complexity of the algorithm, based on H.263 can provide better image quality,The lower rate that is well suited to IP video conferencing, video phone applications.Currently, the largest use of H.263 IP Video Communication is a coding methodMany standard multimedia communication terminals and has been absorbed, such as : ITU-T H.310 (B - ISDN).H.320 (ISDN), H.324 (PSTN), H.323 (LAN, WAN,IFLA).With the rapid increase in computer performance, visual telephony, and video conferencing application (using coefficients image)pure software encoder (codec) that meet the application requirements.H.263 encoder in the frequency of 166MHz pure software on the mainframe coding frame rate up to 60 frames / sec and above,average image quality (using SNR said) than LANIC.The ITU-T H.263 H.263 + 1998 is the second edition,It provides 12 new models and other features can be discussed and further improve the compression performance.Only five format video sources such as H.263, H.263 + allow the use of the source format.Shape and clock frequency, a number of options to broaden the scope of application;

Another important improvement is the scalability,It allows multi-display rate, multi-rate and multi-resolution, and enhanced video information in areas prone to error.Loss easy transmission heterogeneous network environment.

In addition, the base of the image above dependence can be restricted to reduce transmission errors.The movement is not restricted to H.263 H.263 + vector model improvementsplus options for 12 additional models, which not only enhances the coding performance, and enhanced application flexibility.