MPEG: The Standard for Video Compression in Multimedia Applications, Slides of Computer Science

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MPEG: A Video Compression

Standard for Multimedia

Applications

Introduction

• 1980’s technology made possible full-motion video over networks - Television and Computer Video seen moving closer - (Today, Sony and Microsoft are squaring off)
• Needed a standard
  • Often, triggers needed volume production
    • Ala facsimile (fax)
  • Avoid de facto standard by industry
• 1988, Established the Motion Picture Experts Group (MPEG) - Worked towards MPEG- - Primarily video but includes audio (MP3)

Dance of the2 elephants

Outline

• Introduction (done)

• MPEG Goals 

• MPEG Details

• Performance and Such

• Summary

Compatibility Goals

• 1990: CD-ROM and DAT key storage devices
  • 1-2 Mbits/sec for 1x CD-ROM
• Two types of application videos:
  • Asymmetric (encoded once, decoded many)
    • Video games, Video on Demand
  • Symmetric (encoded once, decoded once)
    • Video phone, video mail …
• ( How do you think the two types might influence design ?)
• Video at about 1.5 Mbits/sec
• Audio at about 64-192 kbits/channel

Relevant Standards

• Joint picture Experts Group (JPEG)

• Compress still images only

• Expert Group on Visual Telephony (H.261)

• Compress sequence of images
• Over ISDN (64 kbits/sec)
• Low-delay

• Other high-bandwidth “H” standards:

• H21 (34 Mbits/sec)
• H22 (45 Mbits/sec)

Outline

• Introduction (done)

• MPEG Goals (done)

• MPEG Details 

• Performance and Such

• Summary

Spatial Redundancy

• Take advantage of similarity among most

neighboring pixels

Spatial Redundancy Reduction

• RGB to YUV
  • less information required for YUV (humans less sensitive to chrominance)
• Macro Blocks
  • Take groups of pixels (16x16)
• Discrete Cosine Transformation (DCT)
  • Based on Fourier analysis where represent signal as sum of sine's and cosine’s
  • Concentrates on higher-frequency values
  • Represent pixels in blocks with fewer numbers
• Quantization
  • Reduce data required for co-efficients
• Entropy coding
  • Compress

Groupwork

• When may spatial redundancy reduction be

ineffective? What kinds of images/movies?

Groupwork

• When may spatial redundancy reduction be

ineffective?

• High-resolution images and displays
  • May appear ‘coarse’
• A varied image or ‘busy’ scene
  • Many colors, few adjacent

Temporal Redundancy

• Take advantage of similarity between

successive frames

“Talking Head”

Temporal Activity

Temporal Redundancy Reduction

Temporal Redundancy Reduction

• I frames are independently encoded
• P frames are based on previous I, P frames
  • Can send motion vector plus changes
• B frames are based on previous and following I and P frames
  • In case something is uncovered