• MPEG Motion Picture Expert Group

Moving Picture Encoded Group

Prateek raj gautam(725/09)

MPEG-1 Optimized for bitrates around 1.5 Mbit/s

• mainly designed for error-free digital storage media

• multiplexing of audio, video and data• 352x240 pixels a 30 frames/sec [ NTSC based ]

• 352x288 pixels at 25 frames/sec [ PAL based ]

Applications

• CD, digital multimedia, and video database

(e.g. video-on-demand)

MPEG-2

• 2-15 or 16-80 Mbit/s bit rate

• Applications:

• satellite, cable, and terrestrial broadcasting, digital networks, and digital VCR

Basics of MPEGTypes of pictures frames

I (intra) frame

compressed using only intraframe coding

Moderate compression but faster random access

P (predicted) frame

Coded with motion compression using past I frames or P frames

Can be used as reference pictures for additional motion compensation

B (bidirectional) frame

Coded by motion compensation by either past or future I or P frames

D (DC) frame

Limited use: encodes only DC components of intraframe coding

FRAME SEQUENCE

MPEG Compression is Based on Processing

8 x 8 Pixel Blocks

Only Moving Areas Have to Be Coded

MOTION VECTOR

MOTION VECTOR

• Try to match each block in the actual picture to content in the previous picture. Matching is made by shifting each of the 8 x 8 blocks of the

• Two successive pictures pixel by pixel each direction -> Motion vector

• Substract the two blocks -> Difference block

• Transmit the motion vector and the difference block

MPEG: Video Encoding

Preprocessing

FrameMemory

+ -

DCT

MotionCompensation

MotionEstimation

FrameMemory

+

IDCT

Quantizer(Q)

Regulator

VLCEncoder

BufferQ-1

Output

Input

Pre

dict

ive

fram

e

Mot

ion

vect

ors

MPEG-2 Why another standard?

Support higher bit rates e.g., 80-100 Mbits/s for HDTV instead of the 1.15 Mvits/s for SIF

Support a larger number of applications

The encoding standard should be a toolkit rather than a flat procedure

Interlaced and non-interlaced frame

Different color subsampling modes e.g., 4:2:2, 4:2:0, 4:4:4

Flexible quantization schemes – can be changed at picture level

Scalable bit-streams

Profiles and levels

THANK YOU