The development course of video encode technology Video encode technology is basic it is the H.26x that the MPEG-x that makes by ISO/IEC and ITU-T make of standard of international of encode of video of two old series roll out. From H.261 video encode suggests, wait to have the cause of a joint ceaseless pursuit to H.262/3, MPEG-1/2/4, be in namely as far as possible small yard is led (or memory capacity) next acquisition as far as possible good picture quality. And, transmit the addition of demand to image as the market, how to get used to different channel to transmit characteristic problem to also be shown increasingly. Then Organization for Standardization of two big international made IEO/IEC and ITU-T together H.264 of video new standard will solve these problems.
H.261 is the video encode proposal that appears the earliest, the purpose is the video in the conference TV on normative ISDN net and picturephone application encode technology. The algorithm that it uses was united in wedlock to be able to reduce time to be forecasted between redundant frame and can reduce what the DCT with redundant space alternates to mix encode method. Match with ISDN channel photograph, its output a rate is P × 64kbit/s. P is taken when the value is lesser, can convey the image with not quite high definition only, agree with face-to-face videophone; P is taken when the value is greater (like P ＞ 6) , can transmit the conference TV image with better definition. What H.263 suggests is small yard leads image to reduce a level, in the improvement that H.261 is on the technology and augment, supportive code leads the application that is less than 64kbit/s. But the proposal that substantial H.263 and the H.263 later and H.263 already developed to support entire yard to lead application, from it this can see the image pattern with numerous support, be like Sub-QCIF, QCIF, CIF, 4CIF even the format such as 16CIF.
The code rate of MPEG-1 standard is 1.2Mbit/s left and right sides, can offer 30 frame CIF (352 × 288) the image of quality, the video that is CD-ROM CD stores and broadcast place to make. The basic algorithm of part of encode of MPEG-l standard video and H.261/H.263 are similar, also use athletic compensatory forecast between frame, 2 dimension DCT, VLC swims the measure such as Cheng encode. In addition still introduced inside frame frame (I) , forecast frame (P) , two-way forecast frame (B) with dc frame (D) wait for a concept, improved encode efficiency further. On the foundation of MPEG-1, MPEG-2 standard was raising the respect such as TV of picture resolution, compatible number to do a few improve, for example the precision of its athletic vector is resemble element partly; In encode operation (be like athletic estimation and DCT) " of " of divisional " frame and " field; Introduced encode can classification sexual technology, if the space can classification,gender, time can classification gender and letter a confusion of voices are compared can classification the gender. The standard introduced the MPEG-4 that rolls out in recent years to be based on object of seeing and hearing (AVO: Audio-Visual Object) encode, improved the alternant ability that video corresponds and encode efficiency greatly. A few new technologies still were used in MPEG-4, if appearance codes, get used to encode of object of video of DCT, aleatoric appearance to wait oneself. But the basic video coder of MPEG-4 still is belonged to and H.263 mixes coder one kind similar.
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