H.264 is a video compression standard that provides various encoding options that trade off quality, bitrate, delay, and computational requirements. The document discusses key H.264 encoding concepts like slices, macroblocks, frames, prediction modes, and entropy coding. It explains that the encoder evaluates coding modes for each macroblock based on rate-distortion optimization to minimize the cost function of distortion plus a weighting of bitrate. Practical encoding strategies aim to reduce computational overload by limiting coding modes or approximating the cost calculations.

1. Getting the most out of H.264 17 th November 2010 Iain Richardson

2. H.264 : what’s essential and what’s optional?

4. slices macroblocks frames or fields

6. I slice P slice B slice I MB I P Skip I P Skip B

7. Intra prediction choices

8. Inter prediction choices

10. Quantization Parameter Transform + quantization choices

11. Quantized coefficients Motion vectors Macroblock headers … .. Coded bitstream Exp-Golomb / CAVLC encoder CABAC encoder Entropy coding choices

12. What are the trade-offs?

13. Quality (or Distortion) Rate Computation

14. Example: Group of Pictures structure

15. Encoder choices are based on: Decoder capabilities Video content Computing resources Profile + Level Current + previous statistics Time to encode

16. What’s important? Bitrate Quality Delay Real-time or offline Flexibility

17. H.264 mode decisions

19. MB header and vectors Coded residual Coded macroblock

20. I slice

21. P slice

22. B slice

23. Making the best decisions

24. Cost of coding Quality (or distortion) Bitrate Computation

25. Bitrate PSNR Rate-Distortion Curve for a video clip BETTER WORSE

27. Rate PSNR R-D points for one MB

29. Rate PSNR λ1 λ2

30. For every macroblock: 1. Try out every coding mode, measure D and R 2. Choose mode with minimum J = D + λR  Rate Distortion Optimised (RDO) Mode Selection

31. Rate cost Distortion cost Headers Residual Skip MB Intra MB P MB B MB Distortion J

32. Bitrate PSNR Few modes, no RDO Multiple modes, no RDO Multiple modes, with RDO

33. Computational overload?

34. Practical strategy 1: Reduce the number of modes

36. What’s next?

37. HD content everywhere & not enough bandwidth?

38. Computation increasing on every platform

39. More computation More coding options High Efficiency Video Coding Flexible Coding

40. Summary

41. Questions? onecodec.com www.dcktn.org.uk vcodex.com Email me: iain@onecodec.com elecard.com