MPEG-1 and MPEG-2 Digital Video Coding StandardsOverviewWhat is MPEG?MPEG-1MPEG-2MPEG Video LayersIntra Frame Coding TechniquesVideo FilterSlide 9Statistical RedundancyDiscrete Cosine TransformDCT Basis PatternsSlide 13Variance Distribution of DCT CoefficientsDCT Coefficient QuantizationExample CoefficientsRun-Length EncodingInter Frame Coding TechniquesPicture TypesIntra PicturesPredicted PicturesBi-directional PicturesVideo Stream CompositionVideo Stream vs Display orderMotion EstimationSlide 26Macroblock MatchingSlide 28Coding of Residual ErrorsSlide 30Slide 31Slide 32Slide 33MPEG-1 and MPEG-2 Digital Video Coding StandardsAuthor: Thomas SikoraPresenter: Chaojun LiangOverview•Introduction•Intra-picture Coding Techniques•Inter-picture Coding TechniquesWhat is MPEG?•Stands for Moving Picture Expert Group•Nickname to a family of International standards used for coding audio-visual information in a digital compressed format. •Includes MPEG-1, MPEG-2, and upcoming MPEG-4.MPEG-1•Finalized in 1991•Optimized to work at 352*240, 30 f/s or 352*288, 25f/s•Bit-rate is optimized for application of around 1.5 Mb/sec•Defined for progressive frames onlyMPEG-2•Finalized in 1994•Digital television broadcasting•Target bit-rate raised to 4-9Mb/sec•Main Profile, Main Level–720*480 pixels, 30 frame/sec, 15Mb/sec•Main Profile, High Level (HDTV)–1920*1280 pixels, 30 frame/sec, 80Mb/secMPEG Video LayersIntra Frame Coding TechniquesVideo FilterDCTQuantizerRun-length EncodingBitstream BufferBit-Rate ControlVideo Filter•Subjective Redundancy–Eyes more sensitive to changes in Luminance, less to variations in Chrominance•R G B -> Y Cb Cr•Sample Chrominance 2:1 in both directionsR G B Y Cb Cr Y Cb CrColor Space TransformSampleVideo FilterStatistical RedundancyDiscrete Cosine Transform•Closely related to Discrete Fourier Transform•Performed on 8*8 blockForward DCTInverse DCTDCT Basis PatternsDCT Basis PatternsIncreasing Vertical Frequency (Down)Increase Horizontal Frequency (Right)Variance Distribution of DCT CoefficientsDCT Coefficient Quantization•Higher frequency -> Larger step size -> more coarsely quantized•Force as many of the DCT-Coefficients as possible to zero or near zero)),(),((),(vuQvuFndIntegerRouvuFQExample CoefficientsRun-Length EncodingRun-Amplitude Pairs Bit StreamVariable Length Code TableInter Frame Coding Techniques•Exploit temporal redundancy•Use Motion Estimation to eliminate temporal redundancyPicture Types•Intra Pictures (I-Pictures)•Predicted Pictures (P-Pictures)•Bi-directional Pictures (B-Pictures)Intra Pictures•Coded with only info in the picture itself•Random access points into the compressed data•Moderate compress: about 2 bits per coded pixelPredicted Pictures•Coded with respect to the nearest previous I-Picture or P-PictureBi-directional Pictures•Use both a past and future picture as a reference.Video Stream Composition•Encoder chose frequency and location of I-Pictures•Typical display orderVideo Stream vs Display orderMotion EstimationTree moved down to the rightPeople moved farther to the right than treeFrame 1 Frame 2Motion Estimation•To adequately represent the change, or the difference, between 2 video frames•Frame-wise direct minus not effective•Macroblock-wise minus •2-D spatial search for each luminance macroblockMacroblock MatchingFrame 1 Frame 2Picture 1Predicted PicturePicture 2Residual Error PictureCoding of Residual Errors•Similar to Intra frame coding•Different quantization matrix•Motion vectors are also
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