MPEG Motion Picture Expert Group Moving Picture Encoded Group - PowerPoint PPT Presentation

• 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 MPEG Types 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 Regulator + Frame Quantizer VLC DCT Memory - (Q) Encoder Q -1 Buffer Pre e s m r o processing IDCT a t r c f e e v v n Output i + t o c i i t d Input o e M r Motion P Frame Compensation Memory Motion Estimation

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

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