Transcript Document 7322618

MPEG-1 and MPEG-2
Digital Video Coding Standards
Author: Thomas Sikora
Presenter: Chaojun Liang
Overview
• Introduction
• Intra-picture Coding Techniques
• Inter-picture Coding Techniques
What is MPEG?
• Stands for Moving Picture Expert Group
• Nickname to a family of International
standards used for coding audio-visual
information in a digital compressed format.
• Includes MPEG-1, MPEG-2, and upcoming
MPEG-4.
MPEG-1
• Finalized in 1991
• Optimized to work at 352*240, 30 f/s or
352*288, 25f/s
• Bit-rate is optimized for application of
around 1.5 Mb/sec
• Defined for progressive frames only
MPEG-2
•
•
•
•
Finalized in 1994
Digital television broadcasting
Target bit-rate raised to 4-9Mb/sec
Main Profile, Main Level
– 720*480 pixels, 30 frame/sec, 15Mb/sec
• Main Profile, High Level (HDTV)
– 1920*1280 pixels, 30 frame/sec, 80Mb/sec
MPEG Video Layers
Intra Frame Coding Techniques
Bit-Rate Control
Video
Filter
DCT
Quantizer
Run-length
Encoding
Bitstream
Buffer
Video Filter
• Subjective Redundancy
– Eyes more sensitive to changes in Luminance,
less to variations in Chrominance
• R G B -> Y Cb Cr
• Sample Chrominance 2:1 in both directions
Video Filter
Color Space
Transform
RGB
Sample
Y Cb Cr
Y Cb Cr
Statistical Redundancy
Discrete Cosine Transform
• Closely related to Discrete Fourier
Transform
• Performed on 8*8 block
Forward DCT
Inverse DCT
DCT Basis Patterns
DCT Basis Patterns
Increasing
Vertical
Frequency
(Down)
Increase Horizontal Frequency (Right)
Variance Distribution of DCT Coefficients
DCT Coefficient Quantization
F (u, v)
FQ(u, v)  IntegerRou nd (
)
Q(u, v)
• Higher frequency -> Larger step size ->
more coarsely quantized
• Force as many of the DCT-Coefficients as
possible to zero or near zero
Example Coefficients
Run-Length Encoding
Run-Amplitude Pairs
Bit Stream
Variable Length Code
Table
Inter Frame Coding Techniques
• Exploit temporal redundancy
• Use Motion Estimation to eliminate
temporal redundancy
Picture Types
• Intra Pictures (I-Pictures)
• Predicted Pictures (P-Pictures)
• Bi-directional Pictures (B-Pictures)
Intra Pictures
• Coded with only info in the picture itself
• Random access points into the
compressed data
• Moderate compress: about 2 bits per coded
pixel
Predicted Pictures
• Coded with respect to the nearest previous
I-Picture or P-Picture
Bi-directional Pictures
• Use both a past and future picture as a
reference.
Video Stream Composition
• Encoder chose frequency and location of IPictures
• Typical display order
Video Stream vs Display order
Motion Estimation
Tree moved down
to the right
Frame 1
People moved farther to
the right than tree
Frame 2
Motion Estimation
• To adequately represent the change, or the
difference, between 2 video frames
• Frame-wise direct minus not effective
• Macroblock-wise minus
• 2-D spatial search for each luminance
macroblock
Macroblock Matching
Frame 1
Frame 2
Picture 1
Residual Error Picture
Picture 2
Predicted Picture
Coding of Residual Errors
• Similar to Intra frame coding
• Different quantization matrix
• Motion vectors are also coded