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 or 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

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 Pre processing Frame Memory + - DCT Motion Compensation Motion Estimation Frame Memory + IDCT Quantizer (Q) Regulator VLC Encoder Buffer Q -1 Output Input Predictive frame Motion vectors

MPEG-2 Why another standard?  Support higher bit rates e.g., 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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