A Study on AVS M Video Standard Sahana Devaraju1 and K R Rao1 IEEE Fellow Electrical Engineering Department University of Texas at Arlington Arlington TX E mail sahana devaraju rao uta edu 1 Abstract Audio video standard for Mobile AVS M 1 9 is the seventh part of the most recent video coding standard which is developed by AVS workgroup of China which aims for mobile systems and devices with limited processing and power consumption This paper provides an insight into the AVS M video standard features it offers various data formats it supports profiles and tools that are used in this standard and architecture of AVS M codec A study is done on the key techniques such as transform and quantization intra prediction quarterpixel interpolation motion compensation modes entropy coding and in loop de blocking filter Simulation results are evaluated in terms of bitrates and SNR 1 Introduction Over the past 20 years analog based communication around the world has been sidetracked by digital communication The modes of digital representation of information such as audio and video signals have undergone much transformation in leaps and bounds With the increase in commercial interest in video communications the need for international image and video compression standards arose Many successful standards of audio video signals 18 19 have been released which have advanced a plethora of applications the largest of which is the digital entertainment media Products have been developed which span a wide range of applications and have been enhanced by the advances in other technologies such as the internet and digital media storage Moving Picture Experts Group MPEG 3 was the first group who formed the format which quickly became the standard for audio and video compression and transmission Soon after MPEG 2 was released being broader in scope supported interlacing and high definition video formats Soon later MPEG 4 uses further coding tools with additional complexity to achieve higher compression factors than MPEG 2 MPEG 4 is very efficient in terms of coding being almost 1 4th the size of MPEG 1 Although the MPEG standards have monopoly over most of the video signal formats several other formats also gave close competition in terms of efficiency complexity and storage requirements AVS China 1 8 was developed by the AVS workgroup and is currently owned by China This audio and video standard was initiated by the Chinese government in order to counter the monopoly of the MPEG standards which were costing it dearly AVS China clearly focused on reducing the dependence on audio video information formatting based on the MPEG formats thereby providing China with a standard that helped save millions of dollars of Chinese money being lost to the MPEG group AVS objective was to create a national audio video standard for broadcasting in China and further extend this technology across the globe 2 Data formats AVS supports both progressive and interlaced scan formats 5 Progressive scan is a method of storing or transmitting images where in all lines of each frame are scanned in sequence Interlaced scanning involves alternate run through of odd and even lines AVS codes video data in progressive scan format An advantage of coding data in progressive scan format is the efficiency of motion estimation and also progressive content can be encoded at significantly lower bit rates than interlaced data Motion compensation of progressive content is less complex than interlaced content 2 1 Layered structure AVS follows a layered structure for the data and this is very much visible in the coded bitstream Figure 1 depicts the layered data structure The first layer is a set of frames of video put together as a sequence Video frames comprise the next layer and are called Pictures Pictures are subdivided into rectangular regions called slices Slices are further subdivided into square regions of pixels called macroblocks MB These MBs consist of a set of luminance and chrominance blocks 5 Figure 1 Layered structure 5 2 1 1 Sequence The sequence layer consists of a set of mandatory and optional downloaded system parameters The mandatory parameters are necessary to initialize decoder systems The optional parameters are used for other system settings at the discretion of the network provider Sometimes user data can optionally be contained in the sequence header The sequence layer provides an entry point into the coded video Sequence headers should be placed in the bitstream to support user access appropriately for the given distribution medium Repeat sequence headers may be inserted to support random access Sequences are terminated with a sequence end code 2 1 2 Picture The picture layer provides the coded representation of a video frame 2 4 5 It comprises of a header with mandatory and optional parameters and optionally with user data Three types of pictures are defined by AVS Intra pictures I pictures Predicted pictures P pictures Interpolated pictures B pictures AVS M 6 supports only I picture frame and P picture frame which is depicted in Figure 2 I frame can be reconstructed without any reference to other frames The P frames are forward predicted from the last I frame or P frame i e it is impossible to reconstruct them without the data of another frame I or P P frame can have a maximum of two reference frames for forward prediction Figure 2 Picture types in AVS part 7 2 2 1 3 Slice The slice structure provides the lowest layer mechanism for resynchronizing the bitstream in case of transmission error Slices comprise of a series of MBs Slices must not overlap must be contiguous must begin and terminate at the left and right edges of the picture It is possible for a single slice to cover the entire picture The slice structure is optional Slices are independently coded and no slice can refer to another slice during the decoding process 2 1 4 Macroblock Picture is divided into MBs A macroblock includes the luminance and chrominance component pixels that collectively represent a 16x16 region of the picture In 4 2 0 mode the chrominance pixels are subsampled by a factor of two in each dimension therefore each chrominance component contains only one 8x8 block In 4 2 2 mode the chrominance pixels are subsampled by a factor of two in the horizontal dimension therefore each chrominance component contains two 8x8 blocks 2 4 5 The MB header contains information about the coding mode and the motion vectors It may optionally contain the
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