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MPEG: A Video Compression Standard for Multimedia Applications
MPEG: A Video Compression Standard for Multimedia Applications
Introduction
Introduction
The Need for Video Compression
The Need for Video Compression
Compatibility Goals
Compatibility Goals
Requirements
Requirements
Relevant Standards
Relevant Standards
MPEG Compression
MPEG Compression
Spatial Redundancy
Spatial Redundancy
Spatial Redundancy Reduction
Spatial Redundancy Reduction
Spatial Redundancy Reduction
Spatial Redundancy Reduction
Question
Question
Answer
Answer
Loss of Resolution
Loss of Resolution
Temporal Redundancy
Temporal Redundancy
Temporal Activity
Temporal Activity
Temporal Redundancy Reduction
Temporal Redundancy Reduction
Temporal Redundancy Reduction
Temporal Redundancy Reduction
Temporal Redundancy Reduction
Temporal Redundancy Reduction
Group of Pictures (GOP)
Group of Pictures (GOP)
Question
Question
Answer
Answer
Non-Temporal Redundancy
Non-Temporal Redundancy
Non-Temporal Redundancy
Non-Temporal Redundancy
Typical MPEG Parameters
Typical MPEG Parameters
Typical Compress
Typical Compress
MPEG Today
MPEG Today
MPEG Today
MPEG Today
MPEG Tools
MPEG Tools

Презентация на тему: «MPEG: A Video Compression Standard for Multimedia Applications». Автор: Claypool. Файл: «MPEG: A Video Compression Standard for Multimedia Applications.ppt». Размер zip-архива: 873 КБ.

MPEG: A Video Compression Standard for Multimedia Applications

содержание презентации «MPEG: A Video Compression Standard for Multimedia Applications.ppt»
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1 MPEG: A Video Compression Standard for Multimedia Applications

MPEG: A Video Compression Standard for Multimedia Applications

V?clav Hlav?? CTU Prague, hlavac@cmp.felk.cvut.cz

Initial material were slides of Didier Le Gall, Worcherster Polytechnic Institute.

2 Introduction

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-1 Primarily video but includes audio (MP3)

3 The Need for Video Compression

The Need for Video Compression

High-Definition Television (HDTV) 1920x1080 30 frames per second (full motion) 8 bits for each three primary colors (RGB) ?Total 1.5 Gb/sec! Cable TV: each cable channel is 6 MHz Max data rate of 19.2 Mb/sec Reduced to 18 Mb/sec w/audio + control … ?Compression rate must be ~ 80:1!

4 Compatibility Goals

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 times) 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

5 Requirements

Requirements

Random Access, Reverse, Fast Forward, Search At any point in the stream (within ? second) Can reduce quality somewhat during this task, if needed Audio/Video Synchronization Robustness to errors Not catastrophic if some bits are lost Lends itself to Internet streaming Coding/Decoding delay under 150 ms For interactive applications Ability to Edit Modify/Replace frames

6 Relevant Standards

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)

7 MPEG Compression

MPEG Compression

Compression through Spatial Temporal

8 Spatial Redundancy

Spatial Redundancy

Take advantage of similarity among most neighboring pixels

9 Spatial Redundancy Reduction

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

10 Spatial Redundancy Reduction

Spatial Redundancy Reduction

“Intra-Frame Encoded”

Zig-Zag Scan, Run-length coding

11 Question

Question

When may spatial redundancy reduction be ineffective? What kinds of images/movies?

12 Answer

Answer

When may spatial redundancy elimination be ineffective? High-resolution images and displays May appear ‘coarse’ What kinds of images/movies? A varied image or ‘busy’ scene Many colors, few adjacent

13 Loss of Resolution

Loss of Resolution

Original (63 kb)

Low (7kb)

Very Low (4 kb)

14 Temporal Redundancy

Temporal Redundancy

Take advantage of similarity between successive frames

15 Temporal Activity

Temporal Activity

“Talking Head”

16 Temporal Redundancy Reduction

Temporal Redundancy Reduction

17 Temporal Redundancy Reduction

Temporal Redundancy Reduction

18 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

19 Group of Pictures (GOP)

Group of Pictures (GOP)

Starts with an I-frame Ends with frame right before next I-frame “Open” ends in B-frame, “Closed” in P-frame (What is the difference?) MPEG Encoding a parameter, but ‘typical’: I B B P B B P B B I I B B P B B P B B P B B I Why not have all P and B frames after initial I?

20 Question

Question

When may temporal redundancy reduction be ineffective?

21 Answer

Answer

When may temporal redundancy reduction be ineffective? Many scene changes High motion

22 Non-Temporal Redundancy

Non-Temporal Redundancy

Many scene changes vs. few scene changes

23 Non-Temporal Redundancy

Non-Temporal Redundancy

Sometimes high motion

24 Typical MPEG Parameters

Typical MPEG Parameters

25 Typical Compress

Typical Compress

Performance

Type Size Compression --------------------- I 18 KB 7:1 P 6 KB 20:1 B 2.5 KB 50:1 Avg 4.8 KB 27:1 ---------------------

Note, results are Variable Bit Rate, even if frame rate is constant

26 MPEG Today

MPEG Today

MPEG video compression widely used digital television set-top boxes HDTV decoders DVD players video conferencing Internet video ...

27 MPEG Today

MPEG Today

MPEG-2 Super-set of MPEG-1 Rates up to 10 Mbps (720x486) Can do HDTV (no MPEG-3) MPEG-4 Around Objects, not Frames Lower bandwidth Has some built-in repair (header redundancy) MPEG-7 New standard Allows content-description (ease of searching) MP3, for audio MPEG Layer-3

28 MPEG Tools

MPEG Tools

MPEG tools at: http://www-plateau.cs.berkeley.edu/mpeg/index.html MPEG streaming at: http://www.comp.lancs.ac.uk/ FFMPEG http://ffmpeg.sourceforge.net/index.org.html

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