【 Weak current College 】 high definition video communications application technology and related standards---Power By 【 China power house network 】

As the video communication applications continue to evolve and improve, more and more industry user acceptance and use of video communication products. But in traditional video communication technology standards, because of the video communication application technology and audio/video codec technology development, video communications technology and it is still not fundamentally solve the communication problems of image and sound. Low levels of video quality to satisfy users on high-definition image quality with special needs.

Traditional video communication main question is: after a decoding the image in high resolution, color restore degrees, and a real scene. This phenomenon is due to codec device decoding efficiency low, link dynamically adaptive ability is poor, and many other factors leading to real scenes restore distortion. In addition to audio, traditional 50Hz-7KHz can only feel the narrow width of the audio is not on the spot and sound characteristics of effective restore requires audio codec to provide higher audio sample rate, in order to achieve wider audio effects. In real use, people for the video image and sound of the increasingly high demands, for example: telemedicine, tele-surgery; remote maintenance requires the adoption of video communications this process on the site of the exact video transmission (high-definition video applications). It requires us to provide a higher quality video communication of high-definition video communication products. Therefore digital video company launched a standards-based H.323 H.320; high-definition video communication products NEWVISION7000, NEWVISION8000 series.

High definition video communications technologies of choice:

Video requirements:

Video communications applications as a media applications also need to follow the standards organizations that advocate for high-definition multimedia standards. The current high-definition digital television (HDTV) advocated by video resolution there are three main formats, namely 720P, 1080I, 1080P (where "P" as the progressive scan mode; "I" as interlace mode). And high-definition video communication the main application form: 720P — 720 line by line.

Video communication using progressive scan is that video conference scene usually requires the dynamic images (special areas excluded), the image changes are minor, but on image detail requirements are very high, while also ensuring stability of the image. These are based on 1080i interlace scan (PAL 50 fields per second scan, respectively on the horizontal line and the odd-numbered rows scanned, every field of the actual resolution only 540 lines) are not met and, therefore, in the scanning mode, using progressive scan on a more stable display details, making the picture more clear.

In terms of media streaming, you need a lot of the original video and audio streaming to encode compressed in transmission link for compression and transmission. High-definition audio and video streams (720P) the processing of the video stream is traditional CIF format stream of 10 times. If you use a larger resolution format video images, such as 1080P, will cause the original media stream more huge, thus affecting the video coding efficiency, reduce the communication process in real-time, to increase the delay, but also on image real-time compression test. Therefore, the construction of a video conference system, whether it is building in standard definition or high definition video communications system should be considered the user on the system of construction investment, let the user pay relatively low cost, get the maximum benefits. Too high of a video image format (1080P) media stream handling, this DSP cost increases and the corresponding users increased overall costs, such as video conferencing system peripheral equipment — high-definition display, playback devices, storage devices, and the main video capture device, must comply with the high-definition communications statutes (high-definition video communication is a complete end-to-end system), while the price of these devices are far more than other devices that will make the overall cost increase, thereby giving the user the mileage upgrade is not obvious. Hence, uses 720P video format as the format of the image resolution to make the whole system to achieve the best price/performance ratio, can effectively reduce the user's purchase cost, avoid wasted investment.

In image format display, the current high-definition display device can simultaneously support 4: 3 and 16: 9 two display mode. The majority of traditional video communication system using 4: 3 display mode, and high definition video communications in video format picture type should be adopted more than meets the eye viewing habits of 16: 9 display in place of traditional video conference system using 4: 3 display mode, this is because the screen display area in the vertical resolution (line number) in the same circumstances, the use of 16: 9 display visual area ratio 4: 3 display mode of the Visual area to increase 20 percent, single frame images can accommodate more video information, so that video communication users can gain a greater angle of video images.

Summary of the conclusions is therefore: the high-definition video communication, video image should be the best choice: choose 720P video format, the 16: 9-format high-definition video standard.

Audio requirements:

Video communication is the video and audio, real-time two-way full communication process. In this process we in order to obtain high-definition video, sometimes overlook another significant process — audio communication process. If we are watching high-definition video image, you cannot get a clear, continuous audio effects. This process essentially meaningless, so its importance or even more than video. In traditional video conference system audio technology development is extremely slow, because currently applied to the video phone's audio codec is a compression standard for the transmission of low bandwidth and high coding efficiency, in order to connect the audio signal of the sampling frequency, sampling accuracy and sampling scope indicators do greatly reduced, making the audio clarity and reductive has to a large extent of decay. And is used to storeAnd playback of non-standard real-time compression protocol (such as OGG, MP3, etc), audio fidelity is very low. This to some extent on the scene sound reduction does not meet requirements. Currently in the process of traditional video communication is mainly G.711, G.722, G.722.1, G.728, etc audio standard, only audio width 50Hz-7KHz Mono, and the human ear can perceive the nature of the frequency response capacity can reach 20Hz-20KHz, therefore, on the spot of the restore process too many audio information has caused the loss of a true performance scene. So in high-definition video communication process we will inevitably have a phase-assisted audio processing solution to this problem. Make it a high-definition communications process to near-perfect.

Current international audio processing technology standards are more in the next generation of real-time interactive audio processing can take MPEG-1Layer2 or AAC audio series, the principles of the selection criteria is that the audio frequency range to achieve 22KHz, which almost covers human auditory full scope, even in the high frequency area beyond the scene audio, enabling to get real natural restore and restore when using two-channel stereo playback, so that the whole video communications voice has a stronger sense of approaching CD-quality sound, reach. At the same time in the adaptation of the link bandwidth and codec efficiency to achieve best. The following table lists the AAC's 9 kinds of specifications.

Standard specifications
MPEG-2AACMAIN main standards audio processing, lack of gain control
MPEG-2AACLC use TNS, lack of gain and projections and increase coding efficiency
MPEG-2AACSSR variable sampling methods
MPEG-4AACLC low complexity encoding
MPEG-4AACMAIN primary standards
MPEG-4AACSSR variable sampling methods
MPEG-4AACLD low delay encoding
MPEG-4AACHE efficient encoding
MPEG-4AACLTP long predicted specifications

To sum up, we're on broadband audio support, you can select MPEG-1Layer2 or AAC series standard, in the above list you can see that there are 9 kinds of AAC format to choose from, each format has its own characteristics. In the next generation high definition video communications applications provide users with a level of broadband audio CD is our pursuit.