CSE679: MPEG r MPEG-1 r MPEG-2

MPEG r MPEG: Motion Pictures Experts Group r Standard for encoding videos/movies/motion pictures r Evolving set of standards m MPEG-1, MPEG-2, MPEG-4 r Exploit motion prediction r Apply the similar techniques as JPEG to individual image

MPEG Compression Steps r Data preparation m Similar to JPEG r Data processing m Motion prediction m DCT r Quantization r Entropy encoding

Data Preparation r Subsample Chrominance signals m 4:1:1 in MPEG-1 m NTSC: Y=352*240, C b =C r =176*120 m PAL: Y=352*288, C b =C r =176*144 r Macroblocks m 16*16 samples (pixels) for the luminance component. m 8*8 samples (pixels) for the chrominance component.

Data Processing r Apply motion prediction at the Macroblock level m In most cases, predictive encoding only makes sense for parts of images and not for the whole image. r Motion prediction used to figure out where this macroblock may be in the next frame r Forward prediction m Prediction based on previous frames r Backward prediction m Prediction based on future frames r Bidirectional prediction m Prediction based on both previous and future frames

IPB Frames r I frames m Independently coded and no temporal prediction m Can start decoding once we have an I-frame r P Frames m Forward predicted frames m Based on previous I or P frames r B frames m Bi-directionally predicted frames, based on previous and following I and P frames r Group of Pictures (GOP): Set of frames between two I frames m IBBPBBPBBI or IPPPI, or II r MPEG decoders may have to buffer extra frames of data besides being displayed

DCT r Apply DCT on the 8*8 data blocks m DC coefficients m AC coefficients

Quantization r Apply Quantization on the frequency domain coefficients r Favor low frequency coefficients

Entropy Encoding r Convert 2 dimensional symbols into 1 dimensional series m Use zig-zag or vertical scans r Apply run-length coding on the 1-D series r Apply Huffman coding

Summary of MPEG-1 r Successive frames may have significantly same data r MPEG exploits motion prediction m Apply motion prediction at the Macroblock level m I, P, and B frames r The standard allows the use of I-frame only, I and P frames only or I-, P- and B-frames. r More about MPEG……

MPEG-2 r MPEG-2 strives for a higher resolution. m MPEG-1 is near the maximum data rate of about 1.5Mbits/s. m MPEG-2 targets at 40Mbits/s => high resolution. r MPEG-2 supports four levels m Low, main, high 1440 and high r There are five profiles associated with each level r The low level of MPEG-2 is compatible with MPEG- 1.

Conclusion r MPEG r MPEG-2 m Targets at high resolution m Profiles and levels m Compatible to MPEG-1