A Comparison of MPEG-2 Video, MPEG-4 AVC, and SMPTE VC-1 (Windows Media 9 Video) Matthew Goldman Director of Technology TANDBERG Television

Transcription

1 A Comparison of MPEG2 Video, MPEG4 AVC, and SMPTE VC1 (Windows Media 9 Video) Matthew Goldman Director of Technology TANDBERG Television

2 Terminology 101: Alphabet Soup MPEG2 H.262 MPEG4 Part 2 MPEG4 SP/ASP MPEG4 Part 10 MPEG4 AVC H.264 AVC JVT Windows Media 9 Video (WM9V) SMPTE VC1 The ubiquitous video codec standard used in digital television today Terrestrial Broadcasting, Cable, DBS, DVDV A followon video codec standard not widely used for DTV (therefore not discussed further here!) Advanced Video Codec (AVC) A next generation video codec standard jointly developed by ISO/IEC MPEG and ITUT VCEG A next generation video codec developed by Microsoft now a proposed standard in The SMPTE

3 Realtime Encoding Performance Bitrate MPEG2 Future Advanced Video Encoding Future Realtime Implementation Best possible offline encoding Bitrate for Broadcast Quality Television Time

4 The HD Scenario MPEG2 Future Bit Rate (Mbps) Bit rate for Broadcast Quality HDTV 6 5 Advanced Video Encoding Future Time

5 Applications Video Profiles Application MPEG2 Video (H.262) MPEG4 AVC (H.264) Windows Media 9 Video (SMPTE VC1) Mobile Devices Video Conferencing Baseline Simple Internet Streaming Broadcast Quality (TV, Cinema, etc.) to Progressive display devices Main Main Main Broadcast Quality (TV, Cinema, etc.), Progressive or Interlace High Advanced

6 The Philosophy of Engineering Computational complexity A key factor in determining the technical success or failure of a codec What is Quality? Impact of objective (ratedistortion curve) vs. subjective observations Tool and algorithm choices Need to be taken as a whole, not individually Optimizing for one content selection vs. being efficient for a wide range Bit rates are lower Traditional tool selection & optimization knowledge may not translate directly Theory vs. practice: Analogous issues apply Differences in implementations of AVC and VC1 vary more than differences in the algorithms themselves

7 Design Approaches WM9V/VC1: Lower computational complexity, without significant performance loss MPEG4 AVC: The most complex within reason of practicality Which approach is better? Decision by committee vs. singleminded focus? More diverse knowledge base vs. internally limited? Issues other than technology not discussed here!

8 Comparison of Tools (1) Tool MPEG2 Video (H.262) MPEG4 AVC (H.264) Windows Media 9 Video (SMPTE VC1) Intra Prediction None: MB encoded DC predictors 4x4 Spatial 16x16 Spatial I_PCM Frequency domain Coefficient Picture Coding Type Frame Field Picture AFF Frame Field Picture AFF MB AFF Frame Field Progressive Picture AFF Compensation Block Size 16x16 16x8, 8x16 16x16 16x8, 8x16 8x8 8x4, 4x8 4x4 16x16 16x8, 8x16 8x8 8x4, 4x8 4x4

9 Comparison of Tools (2) Tool MPEG2 Video (H.262) MPEG4 AVC (H.264) Windows Media 9 Video (SMPTE VC1) Vector Precision Full Pel Half Pel Full Pel Half Pel Quarter Pel Full Pel Half Pel Quarter Pel P Frame Feature Single Reference Single Reference Multiple Reference Single Reference B Frame Feature 1 Reference Each Way 1 Reference Each Way Multiple Reference Direct & Spatial Direct Modes Weighted Prediction 1 Reference Each Way

10 Comparison of Tools (3) Tool MPEG2 Video (H.262) MPEG4 AVC (H.264) Windows Media 9 Video (SMPTE VC1) InLoop Filters None DeBlocking DeBlocking Overlap Transform Entropy Coding VLC CAVLC CABAC Adaptive VLC Transform 8x8 DCT 4x4 Integer DCT 8x8 Integer DCT 4x4 Integer DCT 8x4,4x8 Int DCT 8x8 Integer DCT Other Quantization Scaling Matrices Quantization Scaling Matrices Range Reduction InStream Post Processing Control

11 WM9V/VC1 & MPEG4 AVC Differences. Frame n (current) Vector Prediction Transform Quantize Zigzag Scan & Run Length Encode Entropy Coding. Frame nx (reconstructed Frame nx (reconstructed references) references) reconstructed frame Estimation In Loop Filters motion vector Compensation intra coding inter coding predicted block Inverse Transform Intra Coefficient Prediction Inverse Quantize Frequency Domain Intra Prediction VC1. Frame n (current) Vector Prediction Transform Quantize Zigzag Scan & Run Length Encode Entropy Coding Frame nx (reconstructed Frame nx (reconstructed references) references) reconstructed frame Estimation Intra Prediction Mode Select In Loop Filter motion vector Compensation Intra Prediction inter coding intra coding predicted block Spatial Intra Prediction Inverse Transform Inverse Quantize AVC.

12 WM9V/VC1 & MPEG4 AVC Differences. Frame n (current) Vector Prediction Transform Quantize Zigzag Scan & Run Length Encode Entropy Coding Frame nx (reconstructed Frame nx (reconstructed references) references) Estimation motion vector Compensation intra coding inter coding predicted block Intra Coefficient Prediction AVLC. reconstructed frame In Loop Filters Inverse Transform Inverse Quantize VC1. Frame n (current) Vector Prediction Transform Quantize CAVLC/CABAC Zigzag Scan & Run Length Encode Entropy Coding Frame nx (reconstructed Frame nx (reconstructed references) references) Estimation Intra Prediction Mode Select motion vector Compensation Intra Prediction inter coding intra coding predicted block reconstructed frame In Loop Filter Inverse Transform Inverse Quantize AVC.

13 MPEG2 vs. AVC/VC1: Intra Prediction Modes Block to Intra Code MPEG2 Modes MPEG4 AVC Modes (WMV9 similar) MPEG2 DC Pred Horz Pred Vert Pred Plane Pred Prediction Error Signal Encoded

14 MPEG2: Inter Prediction Modes Reference Picture 16x16 Block to Predict 16x8

15 AVC/VC1: Inter Prediction Modes Block to Predict 16x16 16x8 Reference Picture 8x16 8x8 4x4

16 MPEG2 vs. AVC/VC1: Quarter Pel Compensation Comp Options Integer Pixels Half pel (MPEG2) Quarter pel (AVC/VC1)

17 MPEG2 vs. AVC/VC1: InLoop DeBlocking Filter Without InLoop Filter (MPEG2) With InLoop Filter (AVC/WM9V) Picture taken from

18 Performance Comparison Example: Soccer at full ITUR 601 resolution PSNR (db relative) WM9V / MPEG4 AVC MPEG4 ASP MPEG2 optimized MPEG2 reference Bit rate (Mbps)

19 HD Resolutions and Frame Rates Example video bitrate requirements (today) x720p @60 Bit Rate (Mbps) Resolution pels * frame rate (normalized to D1) MPEG2 Advanced Encoding

20 In summary MPEG4 AVC and WM9V/VC1 have the potential for >2x compression efficiency over MPEG2 Video Good results so far Learning and optimizations ongoing (just like MPEG2 in the early days ) MPEG4 AVC and WM9V/VC1 realtime broadcastquality SD/HD encoders are available now Which codec performs better? Depends on the content and the implementation Let the games begin!