A LITERATURE REVIEW ON AVS CODEC By Swaminathan Sridhar Under the guidance of Dr K R Rao and Dr Zhang LITERATURE REVIEW ON AVS CHINA HISTORIC DEVELOPMENT OF AVS CHINA AVS is an acronym for Audio Video standard which is a compression codec for digital Audio and Video developed by China AVS China was developed to potentially replace the usage of the most standard MPEG2 format and is now competing with H 264 AAC and thus limit the royalty fees which Chinese people had to pay for using the common standards like MPEG and VCEG This standard is applied in the fields like HighResolution Digital Broadcast Wireless Communications medium Internet Broadcast media The most commonly implemented Audio and Video coding standards are the ISO IEC JTC1 formulation MPEG series standard and ITU formulation H 26x series video coding standard and G 7 series Audio coding standard At present there are four Audio and Video Coding standards namely MPEG 2 MPEG 4 MPEG 4 AVC AVC AVS China Based on the coding efficiencies MPEG 4 is nearly 1 4 times MPEG 2 and AVC AVS are more than twice of MPEG 2 AVC is only a one video coding standard where as AVS china comprises a set of standard systems of system Audio Video and Media Copyright Management and thus evolves as a second generation source standard On 30th April 2005 AVS standard Video part was approved as the China s National standard The three main characteristics of AVS china are that It is technically an advanced second generation source coding standard and is totally controlled and formulated by China The standard work group law document as formulated is independent It has an international opening on its formulation Process At present AVS china is being used in IP television where in TV programs are Transmitted over the IP protocols and is also being tested for Chinese mobile multimedia broadcasting An Overview on AVS Standard AVS china Primarily aims at providing high definition and high quality video services Since the basic syntax structure of AVS china is very similar to that of MPEG 2 standard it can be easily used in the present widely used MPEG 2 systems except for the fact that it has a higher coding efficiency and has reduced complexity This refers that AVS china is compatible with the existing MPEG 2 systems and has a architecture model very similar to that of H 264 codec AVS China has a similar coding efficiency to that of H 264 except that it has a lower computational complexity AVS china has been divided into various parts and thus dividing the AVS china architecture into various sub fields AVS1 part1 which considers the system for broadcast AVS1 part2 which covers the Video part AVS1 part3 which covers the Audio part AVS1 part6 which includes the recent proposal of china developing its own High Definition Disc Format AVS1 part8 which covers the Video used for mobile AVS1 Part9 which covers the File format ARCHITECTURE OF AVS CHINA VIDEO CODEC INTRA PREDICTION S1 ENTROPY CODING ICT Q INVERSE ICT INVERSE Q MC VIDEO ME FRAME BUFFERS MC represents real time motion interlacing ME represents the mode estimation ICT Q represents the Integer cosine transform quantization INVERSE ICT Q represents the Inverse Integer cosine transform and quantization LOOP FILTERS BIT STREAM SYSTEM LEVEL ARCHITECTURE OF AVS DECODER INTERPRETATIONS FROM THE AVS VIDEO ENCODER In AVS China each block needs to be predicted and the correct prediction method is employed in the encoder architecture to select inter and intra macro blocks The intra prediction method is derived from the neighboring pixels in left and top blocks The unit size of the spatial prediction used is 8x8 since the transform used is an 8x8 integer transform The inter predictions are derived from the neighboring blocks and fields Basically 4 types of block structures are supported namely 8x8 16x16 8x16 and 16x8 The prediction residues are transformed into 8x8 blocks using the 8x8 integer transform The scanning order used is same as that used in the MPEG 2 codec namely the zigzag order but to improvise on this a new scanning order namely VLC coding technique is implemented in AVS China The deblocking process in AVS china acts on the reconstructed reference directly first across the vertical edges and then across the horizontal edges The syntax structure in AVS china is designed such that it is compatible with the existing MPEG 2 systems since these are the widely used systems at present DATA FORMATS IN AVS CHINA AVS codes video data in progressive scan format which is compatible with all contents that originates in the film It is also compatible with the emerging new standard named as the 24p standard for digital films and in future most of the digital films would be converted to this format AVS also supports the interlaced scanning process VIDEO SEQUENCE EXAMPLE SLICE LAYER EXAMPLE MACRO BLOCK FORMATS The fact for using the progressive scan method rather than the interlaced scanning method is that progressive scanning can be done at a comparatively lower bitrates and can be performed at a higher frame rate and also the complexity involved is much lesser AVS is primarily used in broadcast TV with a higher emphasis HDTV which involves a pixel format of 1920x1080 pixels and basically AVS can support upto 16kx16k sized pixels Pixels are coded in luminance chrominance format YCrCb where in each component can have a precision of 8 bits LAYERED DATA STRUCTURE SEQUENCE PICTURE FRAME ENTRY POINT IN BIT STREAM REPRESENTATION OF VIDEO FRAME SLICE STRIP OF MACRO BLOCKS MACRO BLOCK 6 BLOCKS 4 LUMINENCE 2 CHROMINENCE BLOCK 8X8 PIXELS AVS is built on the layered video structure where in the video signals are divided into several frames At the first layer the input video stream is organized into sequences At the second layer the sequences are divided into frames and are termed as pictures At the third layer pictures are divided into rectangular regions called slices At the fourth layer the slices are further divided into square regions called Macro Blocks As already mentioned in the diagram these 6 blocked Macro blocks are further divided into each of 8x8 pixels The sequence pictures and slices begin with unique start codes that allows the decoder to identify them in the received bit stream 2D VLC BASED ENTROPY CODER It is basically implemented for coding the transformed residuals in AVS coding standard Entropy Coding is very essential in image and video compression where its basic function is to eliminate data redundancy
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