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UCSB ECE 160 - Video Compression Techniques

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ECE160 / CMPS182 MultimediaOverview of MPEG-4Composition and Manipulation of MPEG-4 VideosMPEG-4MPEG-1 and MPEG-2Slide 6Slide 7Slide 8VOP-based vs. Frame-based CodingSlide 10VOP-based CodingVOP-based Motion Compensation (MC)Slide 13Slide 14Slide 15Motion Vector CodingTexture CodingSA-DCT Based Coding for Boundary MBsSlide 19Shape CodingBinary Shape CodingModified Modified READ (MMR)Slide 23Context-based Arithmetic Encoding (CAE)Sprite CodingGlobal Motion Compensation (GMC)Synthetic Object Coding in MPEG-42D Mesh Geometry CodingDelaunay triangulation3D Model-Based CodingFace Object Coding and AnimationBody Object Coding and AnimationSlide 36MPEG-4 Object Types, Profiles and LevelsTools for MPEG-4 Natural Visual Object TypesMPEG-4 Natural Visual Object Types and ProfilesMPEG-4 Levels in Simple, Core, and Main Visual ProfilesMPEG-4 Part10 / H.264Slide 42Slide 43MPEG-7Applications using MPEG-7MPEG-7 and Multimedia Content DescriptionMPEG-7 Descriptor (D)Slide 48Slide 49MPEG-7 Description Scheme (DS)MPEG-7 Video SegmentMPEG-7 Video SummaryMPEG-7 Description Denition Language (DDL)MPEG-21 Multimedia FrameworkECE160Spring 2007 Lecture 12Video Compression Techniques1ECE160 / CMPS182MultimediaLecture 12: Spring 2007Video Compression TechniquesMPEG-4, MPEG-7 and BeyondECE160Spring 2007 Lecture 12Video Compression Techniques2Overview of MPEG-4•MPEG-2 is designed for HDTV, i.e. moving photography•MPEG-4: a newer standard designed for computer generated multimedia. Besides compression, it pays greater attention to issues about user interaction.•MPEG-4 departs from its predecessors in adopting a new object-based coding. The next slide illustrates how MPEG-4 videos can be composed and manipulated by simple operations on the visual objects.•Offering higher compression ratios is also beneficial for digital video composition, manipulation, indexing, and retrieval.•The bit-rate for MPEG-4 video now covers a large range between 5 kbps to 10 Mbps.ECE160Spring 2007 Lecture 12Video Compression Techniques3Composition and Manipulation of MPEG-4 VideosECE160Spring 2007 Lecture 12Video Compression Techniques4MPEG-4•MPEG-4 is an entirely new standard for:(a) Composing media objects to create desirable audiovisual scenes.•(b) Multiplexing and synchronizing the bitstreams for these media data entities so that they can be transmitted with guaranteed Quality of Service (QoS).•(c) Interacting with the audiovisual scene at the receiving end - provides a toolbox of advanced coding modules and algorithms for audio and video compressions.ECE160Spring 2007 Lecture 12Video Compression Techniques5MPEG-1 and MPEG-2Interaction is outside the standardECE160Spring 2007 Lecture 12Video Compression Techniques6MPEG-4ECE160Spring 2007 Lecture 12Video Compression Techniques7Overview of MPEG-4•Video Object Oriented Hierarchical Description of a Scene in MPEG-4 Visual Bitstreams.–The hierarchical structure of MPEG-4 visual bitstreams is very different from MPEG-1 and -2, It is very much video object-oriented.ECE160Spring 2007 Lecture 12Video Compression Techniques8Overview of MPEG-4•Video-object Sequence (VS) - delivers the complete MPEG-4 visual scene, which may contain 2-D or 3-D natural or synthetic objects.•Video Object (VO) - a particular object in the scene, which can be of arbitrary (non-rectangular) shape corresponding to an object or background of the scene.•Video Object Layer (VOL) - facilitates a way to support (multi-layered) scalable coding. A VO can have multiple VOLs under scalable coding, or have a single VOL under non-scalable coding.•Group of Video Object Planes (GOV) - groups Video Object Planes together (optional level).•Video Object Plane (VOP) - a snapshot of a VO at a particular moment.ECE160Spring 2007 Lecture 12Video Compression Techniques9VOP-based vs. Frame-based Coding•MPEG-1 and -2 do not support the VOP concept, and hence their coding method is referred to as frame-based (also known as Block-based coding).ECE160Spring 2007 Lecture 12Video Compression Techniques10VOP-based vs. Frame-based CodingA possible example in which two potential matchesyield small errors for block-based coding.Each VOP is of arbitrary shape and will obtain a uniquemotion vector consistent with the actual object motion.ECE160Spring 2007 Lecture 12Video Compression Techniques11VOP-based Coding•MPEG-4 VOP-based coding also employs the Motion Compensation technique:–An Intra-frame coded VOP is called an I-VOP.–The Inter-frame coded VOPs are called P-VOPs if only forward prediction is employed, or B-VOPs if bi-directional predictions are employed.•The new difficulty for VOPs: may have arbitrary shapes, shape information must be coded in addition to the texture of the VOP.Note: texture here actually refers to the visual content, that is the gray-level (or chroma) values of the pixels in the VOP.ECE160Spring 2007 Lecture 12Video Compression Techniques12VOP-based Motion Compensation (MC)•MC-based VOP coding in MPEG-4 again involves three steps:(a) Motion Estimation.(b) MC-based Prediction.(c) Coding of the prediction error.•Only pixels within the VOP of the current (Target) VOP are considered for matching in MC.•To facilitate MC, each VOP is divided into many macroblocks (MBs). MBs are by default 16x16 in luminance images and 8x8 in chrominance images.ECE160Spring 2007 Lecture 12Video Compression Techniques13VOP-based Motion Compensation (MC)•MPEG-4 defines a rectangular bounding box for each VOP.–The macroblocks that are entirely within the VOP are referred to as Interior Macroblocks.–The macroblocks that straddle the boundary of the VOP are called Boundary Macroblocks.•To help matching every pixel in the target VOP and meet the mandatory requirement of rectangular blocks in transform codine (e.g., DCT), a pre-processing step of padding is applied to the Reference VOPs prior to motion estimation.Note: Padding only takes place in the Reference VOPs.ECE160Spring 2007 Lecture 12Video Compression Techniques14VOP-based Motion Compensation (MC)•Padding–For all Boundary MBs in the Reference VOP, Horizontal Repetitive


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