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1、ERROR CONCEALMENT TECHNIQUES IN H.264/AVC, FOR VIDEO TRANSMISSION OVER WIRELESS NETWORKS,Vineeth Shetty Kolkeri University of Texas, Arlington,Outline,Introduction What is Error Concealment? Error Concealment Architecture H.264/MPEG-4 AVC Overview Error Concealment algorithm Error Concealment perfor
2、mance analysis test results Conclusions Future Work References,Introduction,Figure 1: Typical Situation of 3G/4G cellular telephony,What is Error Concealment?,The operation adopted to reconstruct lost information for video transmission over wireless networks. Need: Compatible with all video streamin
3、g devices. Applications: Recovery of lost information which is comparable with encoded video sequence with minimal complexity.,Error Concealment Architecture,Overview of H.264 / AVC,Latest Video coding standard Basic design architecture similar to MPEG-x or H.26x Better compression efficiency Upto 5
4、0% bitrate reduction from the preceding video codec standard Subjective quality is better Advanced functional element Wide variety of applications such as video broadcasting, video streaming, video conferencing, D-Cinema, HDTV. Layered structure - consists of two layers: Network Abstraction Layer (N
5、AL) and Video Coding Layer (VCL); supports 4:2:0 chroma sampling picture format including QCIF and CIF formats,Overview of H.264 / AVC (contd.),Uses hybrid block based video compression techniques such as: Transformation - reduction of spatial correlation Quantization - bit-rate control Motion compe
6、nsated prediction - reduction of temporal correlation Entropy coding - reduction in statistical correlation Includes the following features: Intra-picture prediction 4x4 integer transform Multiple reference pictures Variable block sizes Quarter pel precision for motion compensation In-loop de-blocki
7、ng filter Improved entropy coding,H.264/AVC Profiles,Profiles and Levels for particular applications Profile : a subset of entire bit stream of syntax, different decoder design based on the Profile Four profiles : Baseline, Main, Extended and High,Streaming Video,Extended,Digital Storage Media Telev
8、ision Broadcasting,Main,Video Conferencing Videophone,Baseline,Applications,Profile,Studio editing,High,Specific coding parts for the Profiles,Specific coding parts for the Profiles (contd.),Common coding parts for the Profiles I slice (Intra-coded slice) : the coded slice by using prediction only f
9、rom decoded samples within the same slice P slice (Predictive-coded slice) : the coded slice by using inter prediction from previously-decoded reference pictures, using more than one motion vector and reference index to predict the sample values of each block CAVLC (Context-based Adaptive Variable L
10、ength Coding) for entropy coding,Specific coding parts for the Profiles (contd.),Coding parts for Baseline Profile Common parts : I slice, P slice, CAVLC FMO Flexible macroblock order : macroblocks may not necessarily be in the raster scan order. The map assigns macroblocks to a slice group ASO Arbi
11、trary slice order : the macroblock address of the first macroblock of a slice of a picture may be smaller than the macroblock address of the first macroblock of some other preceding slice of the same coded picture RS Redundant slice : This slice belongs to the redundant coded data obtained by same o
12、r different coding rate, in comparison with previous coded data of same slice,H.264 Encoder (contd.),H.264 - Transform,4x4 multiplier-free integer transform Transform coefficients perfectly invertible Hierarchical structure - 4 x 4 Integer DCT, Hadamard transform Hadamard transform applied when (16x
13、16) intra prediction mode is used with (4x4) integer DCT MB size for chroma depends on 4:2:0, 4:2:2 and 4:4:4 formats,YUV different formats,4:4:4 is full bandwidth YUV video, and each macroblock consists of 4 Y blocks, and 4 U/V blocks. Being full bandwidth, this format contains as much as data woul
14、d if it were in the RGB color space. 4:2:2 contains half as much chrominance information as 4:4:4 and 4:2:0 contains one quarter of the chrominance information.,H.264 Transform (contd.),Codec - A video codec is software that can compress a video source (encoding) as well as play compressed video (de
15、compress). CIF - Common Intermediate Format - a set of standard video formats used in videoconferencing, defined by their resolution. The original CIF is also known as Full CIF (FCIF). QCIF - Quarter CIF (resolution 176x144) SQCIF - Sub quarter CIF (resolution 128x96) 4CIF - 4 x CIF (resolution 704x
16、576) 16CIF - 16 x CIF (resolution 1408x1152,H.264 Transform (contd.),H.264 - Scaling and Quantization,Multiplication operation for exact transform combined with multiplication of scalar quantization Scale factor for each element in each sub-block varies as a function of quantization parameter associated with macro-block that contains sub block; position of element within sub-block Rate-control algorithm in encoder controls value of quantization parameter Encoder performs post-sc
