加权块匹配算法实现MPEG-2视频编码输出码流中的差错隐蔽..docVIP

The MPEG-2 Standard The quality of MPEG-1 compressed video at 1.2Mbps has been found unacceptable for most entertainment applications. Subjective tests indicate that CCIR601 video can be compressed with excellent quality at 4-6Mbps. MPEG-2 is intended as a compatible extension of MPEG-1 to serve a wide range of applications at various bit-rates (2-20Mbps) and resolutions. Main features of the MPEG-2 syntax are:(1) it allows for interlaced inputs ,higher –definition inputs, and alternative subsampling of the chroma channels,(2) it offers a scalable bit stream ,and (3) it provides improved quantization and coding options. Considering the practical difficulties with the implementation of the full syntax on a single chip, subsets of the full syntax have been specified under five “profiles”, and high profile. Furthermore, a number of “levels” have been introduced within these profiles to impose constraints on some of the video parameters [ISO 93]. It is important to note that the MPEG-2 standard has not yet been finalized. The syntax of the Main Profile was frozen in March 1993. However, work in other profiles is still ongoing. It is likely that the all-digital HDTV compression algorithm will conform with one of the profiles in MPEG-2. MPEG-2 Macroblocks A macroblock(MB) refers to four 8×8luminance blocks and the spatially associated chroma blocks. MPEG-2 allows for three chroma subsampling formats, 4：2：0 (same as MPEG-1), 4：2：2 (chroma subsampled in the horizontal direction only),and 4：4：4 (no chroma subsampling). Therefore, in MPEG-2 a MB may contain 6(4luma,1Cr,and 1Cb),8(4 luma,2Cr,and 2Cb),or 12(4luma, 4Cr,and 4Cb) 8×8blocks. Coding Interlaced Video MPEG-2 accepts both progressive and interlaced inputs. If the input is interlaced, the output of the encoder consists of a sequence of fields that are separated by the field period. There are two options in coding interlaced video :(1) every field can be encoded independently (field pictures); or (2) two fields may be