Study of AVS China Part 7 for Mobile ApplicationsBy Jay MehtaEE 5359 Multimedia ProcessingSpring 20101Contents• 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• References2AVS 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]. 3Table.1 Different parts of AVS-China [3]PartCategory1System2Video3Audio4Conformance test5Reference Software6Digital media rights management7Mobile video8Transmit AVS via IP network9AVS file format10Mobile speech and audio coding4Table.2 Application based profiles of AVS [16]ProfilesKey applicationsJizhun profile(base)Television broadcasting, HDTV, etc.Jiben profile(basic)Mobility applications, etc.Shenzhan profile(extended)Video surveillance, etc.Jiaqiang profile(enhanced)Multimedia entertainment, etc.5Introduction to AVS M • AVS is a set of integrity standard system – system video, audio and media copyright management.• AVS M is the 7thpart 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.6Picture• 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.7Picture• 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.8Slice• 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.9Macroblocks 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.10AVS M encoder [10]11AVS 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.12AVS 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.13AVS M Decoder [10]14Profiles 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 Mbps15Major 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 resilience16Network 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.17Transform [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.18Quantization• 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.19Intra Prediction[3]• Two Types• Intra _4x4 • Direct Intra Prediction(DIP)• Significant complexity reduction • Maintains comparable performanceIntra_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
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