Overview: Video Coding Standards

Transcription

1 Overview: Video Coding Standards Video coding standards: applications and common structure Relevant standards organizations ITU-T Rec. H.261 ITU-T Rec. H.263 ISO/IEC MPEG-1 ISO/IEC MPEG-2 ISO/IEC MPEG-4 Recent progress: H.264/AVC Bernd Girod: EE398B Image Communication II Video Coding Standards: MPEG-1,2,4 no. 1

2 ISO/IEC MPEG MPEG-1 Standard (1991) (ISO/IEC 11172) Target bit-rate about 1.5 Mbps Typical image format CIF, no interlace Frame rate fps Main application: video storage for multimedia (e.g., on CD-ROM) MPEG-2 Standard (1994) (ISO/IEC 13818) Extension for interlace, optimized for TV resolution (NTSC: 704 x 480 Pixel) Image quality similar to NTSC, PAL, SECAM at 4-8 Mbps HDTV at 20 Mbps MPEG-4 Standard (1999) (ISO/IEC 14496) Object based coding Wide-range of applications, with choices of interactivity, scalability, error resilience, etc. Bernd Girod: EE398B Image Communication II Video Coding Standards: MPEG-1,2,4 no. 2

3 MPEG-1/2: GOP Structure "Group of Pictures" = GOP, GOP structure is very flexible I-Picture P-Picture P-Picture B-Pictures time Bernd Girod: EE398B Image Communication II Video Coding Standards: MPEG-1,2,4 no. 3

4 MPEG-1 Encoder Preprocessing Picture reordering - DCT Weighting Quantization VLC Video multiplex Buffer Video in Inverse quantization Inverse weighting Motion vectors, macroblock info, start codes Inverse DCT Bitstream zero Picture store 1 + 1/2 + Motion compensation Picture store 2 Bernd Girod: EE398B Image Communication II Video Coding Standards: MPEG-1,2,4 no. 4

5 MPEG-1: coding of I-pictures I-pictures: intraframe coded 8x8 DCT Arbitrary weighting matrix for coefficients Differential coding of DC-coefficients Uniform quantization Zig-zag-scan, run-level-coding Entropy coding Unfortunately, not quite JPEG Bernd Girod: EE398B Image Communication II Video Coding Standards: MPEG-1,2,4 no. 5

6 MPEG-1: coding of P-pictures Motion-compensated prediction from an encoded I-picture or P-picture (DPCM) Half-pel accuracy of motion compensation, bilinear interpolation One displacement vector per macroblock Differential coding of displacement vectors Coding of prediction error with 8x8-DCT, uniform threshold quantization, zig-zag-scan as in I-pictures Bernd Girod: EE398B Image Communication II Video Coding Standards: MPEG-1,2,4 no. 6

7 MPEG-1: coding of B-pictures Motion-compensated prediction from two consecutive P- or I-pictures either only forward prediction (1 vector/macroblock) or only backward prediction (1 vector/macroblock) or Average of forward and backward prediction = interpolation (2 vectors/macroblock) Half-pel accuracy of motion compensation, bilinear interpolation Coding of prediction error with 8x8-DCT, uniform quantization, zig-zag-scan as in I-pictures Bernd Girod: EE398B Image Communication II Video Coding Standards: MPEG-1,2,4 no. 7

8 MPEG-2 vs. MPEG-1 Efficiently compress interlaced digital video at broadcast quality Field/frame pictures Chroma sampling New prediction modes Field/frame DCT Additional scan patterns for DCT coefficients Motion compensation with blocks of size 16x8 pels Improved coding efficiency by different quantization, VLC tables Various scalability modes Bernd Girod: EE398B Image Communication II Video Coding Standards: MPEG-1,2,4 no. 8

9 Coding of Interlaced Video (1) Frame and field picture structures Bernd Girod: EE398B Image Communication II Video Coding Standards: MPEG-1,2,4 no. 9

10 Coding of Interlaced Video (2) Field prediction for field pictures Bernd Girod: EE398B Image Communication II Video Coding Standards: MPEG-1,2,4 no. 10

11 Coding of Interlaced Video (3) Field prediction for frame pictures Bernd Girod: EE398B Image Communication II Video Coding Standards: MPEG-1,2,4 no. 11

12 Coding of Interlaced Video (4) Dual prime for P pictures Bernd Girod: EE398B Image Communication II Video Coding Standards: MPEG-1,2,4 no. 12

13 Coding of Interlaced Video (5) Field/frame DCT Alternate Scan Bernd Girod: EE398B Image Communication II Video Coding Standards: MPEG-1,2,4 no. 13

14 MPEG-4 Support highly interactive multimedia applications as well as traditional applications Advanced functionalities: interactivity, scalability, error resilience Coding of natural and synthetic audio and video, as well as graphics Enable the multiplexing of audiovisual objects and composition in a scene Computer Interactivity TV/film AV-data Telecom Wireless Video on LANs, Internet video Wireless video Video database Interactive home shopping Video , home movies Virtual reality games, flight simulation, multi-viewpoint training Bernd Girod: EE398B Image Communication II Video Coding Standards: MPEG-1,2,4 no. 14

15 MPEG-4: Scene with audiovisual objects Bernd Girod: EE398B Image Communication II Video Coding Standards: MPEG-1,2,4 no. 15

16 MPEG-4: Video coding Basic video coding Definition of Video Object (VO), Video Object Layer (VOL), Video Object Plane (VOP) Improved coding efficiency vs. MPEG-1/2 Based on H.263 baseline Global motion compensation Sprites Quarter pixel motion compensation Bernd Girod: EE398B Image Communication II Video Coding Standards: MPEG-1,2,4 no. 16

17 MPEG-4: Video coding Object-based video coding Binary shape coding α-map shape coding Padding for block-based DCT of texture Shape-adaptive DCT DWT for still texture coding Mesh animation, face and body animation Bernd Girod: EE398B Image Communication II Video Coding Standards: MPEG-1,2,4 no. 17

18 Shape Adaptive DCT Bernd Girod: EE398B Image Communication II Video Coding Standards: MPEG-1,2,4 no. 18