Download - MPEG_I
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MPEG: A Video Compression Standard for Multimedia Applications
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OutlineIntroductionMPEG GoalsMPEG DetailsPerformance and SuchSummary
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Introduction1980s technology made possible full-motion video over networksNeeded a standardOften trigger needed volume productionAla facsimile (fax)Avoid de facto standard by industry1988, Established the Motion Picture Experts Group (MPEG)Worked towards MPEG-1
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The Need for Video CompressionHigh-Definition Television (HDTV)1920x1080 30 frames per second (full motion)8 bits for each three primary colorsTotal 1.5 Gb/sec!Each cable channel is 6 MHzMax data rate of 19.2 Mb/secReduced to 18 Mb/sec w/audio + control Compression rate must be 83:1!
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Compatibility GoalsCD-ROM and DAT key storage devices1-2 Mbits/sec for 1x CD-ROMTwo types of application videos:Asymmetric (encoded once, decoded many)Video games, Video on DemandSymmetric (encoded once, decoded once)Video phone, video mail (How do you think the two types might influence design?)Video at about 1.5 Mbits/secAudio at about 64-192 kbits/channel
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MPEG CompressionCompression throughSpatialTemporal
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Spatial RedundancyTake advantage of similarity among most neighboring pixels
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Spatial Redundancy ReductionRGB to YUV less information required, same visuallyMacro BlocksTake groups of pixelsDCTRepresent pixels in blocks with fewer numbersQuantizationReduce data required for co-efficientsEntropy codingCompress
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Spatial Redundancy ReductionZig-Zag Scan,Run-length codingIntra-FrameEncoded
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GroupworkWhen may spatial redundancy reduction be ineffective? What kinds of images/movies?
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GroupworkWhen may spatial redundancy reduction be ineffective?High-resolution images and displaysMay appear coarseA varied image or busy sceneMany colors, few adjacent
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Loss of ResolutionOriginal (63 kb)Low (7kb)Very Low (4 kb)
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Temporal RedundancyTake advantage of similarity between successive frames950951952(Simpsons News Clip Here)
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Talking HeadTemporal Activity
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Temporal Redundancy Reduction
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Temporal Redundancy Reduction
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Temporal Redundancy ReductionI frames are independently encodedP frames are based on previous I, P framesB frames are based on previous and following I and P framesIn case something is uncovered
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Group of Pictures (GOP)Starts with an I-frameEnds with frame right before next I-frameOpen ends in B-frame, Closed in P-frame(What is the difference?)MPEG Encoding parameter, but typical:I B B P B B P B B II B B P B B P B B P B B IWhy not have all P and B frames?
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GroupworkWhen may temporal redundancy reduction be ineffective?Many scene changesHigh motion
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Non-Temporal Redundancy Many scene changes
(Mixbag clip here)
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Non-Temporal Redundancy Sometimes high motion(Simpons News Clip here)(Hockey Clip here)
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Sequence LayerGroup of Pictures Layer
MPEG Layers
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MPEG TodayMPEG video compression widely useddigital television set-top boxesHDTV decodersDVD playersvideo conferencingInternet video...
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MPEG TodayMPEG-2Super-set of MPEG-1Rates up to 10 Mbps (720x486)Can do HDTV (no MPEG-3)MPEG-4Around Objects, not FramesLower bandwidthMPEG-7Not (yet) a standardAllows content-description (ease of searching)MP3For audioMPEG Layer-3