Study of AVS China Part 7 for Mobile Applications By Jay Mehta EE 5359 Multimedia Processing Spring 2010 1 Contents Parts and profiles of AVS Standard Introduction to Audio Video Standard for Mobile Applications AVS M AVS M Codec Profiles and levels Major and minor tools used in AVS M Error Concealment and Resilience Conclusions Results List of Acronyms References 2 AVS Standard Audio video coding standard AVS is a working group of audio and video coding standard in China which was established in 2002 Based on versatile applications in the area of video AVS China is categorized into various profiles 16 AVS China consists of four profiles namely Jizhun base profile Jiben basic profile Shenzhan extended profile and Jiaqiang enhanced profile defined in AVS video targeting to different applications Table 2 16 3 Part Category 1 System 2 Video 3 Audio 4 Conformance test 5 Reference Software 6 Digital media rights management 7 Mobile video 8 Transmit AVS via IP network 9 AVS file format 10 Mobile speech and audio coding Table 1 Different parts of AVS China 3 4 Profiles Key applications Jizhun profile base Television broadcasting HDTV etc Jiben profile basic Mobility applications etc Shenzhan profile extended Video surveillance etc Jiaqiang profile enhanced Multimedia entertainment etc Table 2 Application based profiles of AVS 16 5 Introduction to AVS M AVS is a set of integrity standard system system video audio and media copyright management AVS M is the 7th part of the video coding standard developed by the AVS Workgroup of China which aims for mobile systems and devices In AVS M a Jiben Profile has been defined which has 9 different levels AVS follows a layered structure for the data and this representation is seen in the coded bitstream Sequence layer provides an entry point into the coded video It consists of a set of mandatory and optional downloadable parameters 6 Picture The picture layer provides the coded representation of a video frame It comprises a header with mandatory and optional parameters and optionally with user data There are 3 types of pictures defined by the AVS I Pictures P Pictures B Pictures 4 2 0 Sub sampling format is used in AVS M 7 Picture AVS M supports only I picture and P picture which are shown in Figure 1 AVS M supports only progressive video sequence Therefore one picture is one frame P picture can have a maximum of two reference frames for forward prediction 8 Slice Series of Macro Blocks Must not overlap must be contiguous must begin and terminate at the left and right edges of the picture A single slice can cover the entire picture Slices are independently coded so no slice can refer to another slice during the decoding process 9 Macroblocks and blocks Picture is divided into macroblocks The upper left sample of each MB should not exceed picture boundary Macroblock partitioning is used for motion compensation The number in each rectangle specifies the order of appearance of motion vectors 10 AVS M encoder 10 11 AVS M Codec Each and every input MB needs to either intra predicted or inter predicted In an AVS M Encoder S0 is used to select the right prediction method for the current MB whereas in the Decoder the S0 is controlled by the MB type of current MB The intra predictions are derived from the neighboring pixels in the left and top blocks The unit size of intra prediction is 4x4 because of the 4x4 integer cosine transform used by the AVS M The inter predictions are derived from the decoded frames AVS M employs an adaptive variable length coding VLC coding technique 12 AVS M Codec The reconstructed image is the sum of the prediction and current reconstructed error image AVS M uses the deblocking filter in motion compensation loop The deblocking process directly acts on the reconstructed reference first across vertical edges and then across horizontal edges 13 AVS M Decoder 10 14 Profiles and levels 3 AVS M defies Jiben profile which has 9 levels 1 0 up to QCIF and 64 kbps 1 1 up to QCIF and 128 kbps 1 2 up to CIF and 384 kbps 1 3 up to CIF and 768 kbps 2 0 up to CIF and 2 Mbps 2 1 up to HHR and 4 Mbps 2 2 up to SD and 4 Mbps 3 0 up to SD and 6 Mbps 3 1 up to SD and 8 Mbps 15 Major and Minor tools of AVS M Network Abstraction layer NAL Supplemental Enhancement Information SEI Transform 4x4 integer transform Quantization and scaling scaling only in encoder Intra prediction 9 modes simple 4x4 intra prediction and direct intra prediction Motion compensation 16x16 16x8 8x16 8x8 8x4 4x8 4x4 modes Quarter pixel interpolation 8 tap horizontal interpolation filter and 4 tap vertical interpolation filter Simplified in loop deblocking filter Entropy coding Error resilience 16 Network Abstraction Layer NAL 7 In AVS M Video compression a compressed video bitstream is made up of Access units AUs AU contains information for decoding a picture AU consists a no of NAL units some of them are optional A NAL unit can be a sequence parameter set SPS a picture parameter set PPS an SEI a picture header or a slice layer rbsp raw byte sequence payload which consists of a slice header followed by slice data 17 Transform 7 4x4 is the unit of transform intra prediction and smallest motion compensation in AVS M The 4x4 transform used in AVS M is AVS M uses a prescaled integer transform PIT technology all of the scale related operations have been done in the encoder The decoder does not need any scale operations PIT is used in AVS M to reduce complexity 18 Quantization It is performed by the adaptive uniform quantizer on the transform coefficients The step size of the quantizer can be varied to provide rate control The transmitted step size quantization parameter is used directly for luminance coefficients and for chrominance coefficients it is modified on the upper end of its range The quantization parameter varies from 0 to 63 in steps of one 19 Intra Prediction 3 Two Types Intra 4x4 Direct Intra Prediction DIP Significant complexity reduction Maintains comparable performance Intra 4x4 Each 4x4 block is predicted from spatially neighboring samples For each 4x4 block one of the nine predictions modes can be utilized to exploit spatial correlation including eight directional prediction modes such as Down Left vertical etc and non directional prediction mode DC 20 Intra Prediction 3 The 16 samples of the 4x4 block which are labeled as ap are predicted using prior decoded samples in adjacent block label as A D E H and X The up right pixels used to predict are expanded by pixel
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