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MPEG

MPEG. Video Compression. Video compression is based on two principles. The frist is spatial redundancy that exist in each frame and temporal redundancy that a video frame is very similar to its intermediate neighbors. MPEG. The Moving Picture Experts Group Standard for video compression

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MPEG

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  1. MPEG

  2. Video Compression • Video compression is based on two principles. The frist is spatial redundancy that exist in each frame and temporal redundancy that a video frame is very similar to its intermediate neighbors.

  3. MPEG • The Moving Picture Experts Group • Standard for video compression • Similarities with JPEG • Video • Spatial redundancy • Intraframe coding • Temporal redundancy • Interframe coding • Perceptual redundancy

  4. Fundamentals of MPEG • A sequence of 2D images • Temporal correlation as well as spatial correlation • TV broadcast • Frame-based • Field-based

  5. MPEG Standards • MPEG-1: Initial video and audio compression standard. Later used as the standard for Video CD, and includes the popular Layer 3 (MP3) audio compression format. • MPEG-2: Transport, video and audio standards for broadcast-quality television. Used for over-the-air digital television ATSC, DVB and ISDB, digital satellite TV services like Dish Network, digital cable television signals, SVCD, and with slight modifications, as the .VOB (Video OBject) files that carry the images on DVDs. • MPEG-3: Originally designed for HDTV, but abandoned when it was realized that MPEG-2 (with extensions) was sufficient for HDTV. (not to be confused with MP3, which is MPEG-1 Audio Layer 3.) • MPEG-4: Expands MPEG-1 to support video/audio "objects", 3D content, low bitrate encoding and support for Digital Rights Management

  6. Frame Types in MPEG • Intra frames (I-frames) • A I-frame is encoded using only information from within that frame (intra coded) -- no temporal compression (inter coded). • Non-intra frames (P-frames and B-frames) • motion compensated information will be used for coding. • P frame (predicted frame) use preceding frame as reference image • B frame (bidirectional frame) use both preceding frame and following frame as reference images

  7. A sequence of one I-frame followed by P- and B-frames is known as a GOP • Group of Pictures • E.g. IBBPBBPBBPBBP

  8. I-frames • Intraframe coded • No motion compensation • P-frames • Interframe coded • Motion compensation • Based on past frames only • B-frames • Interframe coded • Motion compensation • Based on past and future frames

  9. Motion-compensated prediction • Divide current frame, i, into disjoint 16×16 macroblocks • Search a window in previous frame, i-1, for closest match • Calculate the prediction error • For each of the four 8×8 blocks in the macroblock, perform DCT-based coding • Transmit motion vector + entropy coded prediction error (lossy coding)

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