MPEG: Macroblock Coding,MPEG-2

MPEG: Macroblock Coding





•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
  
 MPEG-2: Effects of Interlacing
 
•Fields or frame pictures can be encoded
•Prediction Modes and Motion Compensation
–Frame prediction: current frame predicted from previous frame
–Field prediction:
•Top and bottom fields of reference frame predicts first field
•Bottom field of previous frame and top field of current frame predicts the bottom field of current frame
–16 X 8 motion compensation mode
•A macroblock may have two of them
•A B picture macroblock  may have four!
–Dual prime motion compensation
•Top field of current frame is predicted from two motion vectors coming from the top and bottom field of reference frame
•Works for P vectors
 
MPEG-2 Applications
 
•Digital Betacam: 90 Mbits/s video
•MPEG-2
–Main Profile, Main Level, 4:2:0: 15 Mbits/s
–High Profile, High Level, 4:2:0: adequate, expensive
–Image quality preserved across generations of processing
–Multiview Profile
•Stereoscopic view – disparity prediction
•Virtual walk-throughs composed from multiple viewpoints
 
 

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