1. Direct Access Video Streaming Scheme Supporting Effective Error Concealment Chun-Ming Huang, Kai-Chao Yang and Jia-Shung Wang

2. Outline Introduction Hierarchical Coding Scheme Center-weighted Hierarchical Coding Scheme Proximity Approximation Questions in the Hierarchical Structure Modified Sequential Coding Scheme Decoder Error Concealment Error Concealment in Hierarchical Coding Structure Error Concealment in Modified Sequential Coding Structure Conclusion and Future Work

3. Introduction VCR Operation  Stop-Resume, Pause-Resume, Slow motion, Jump, Fast Forward Scan, Back Forward Scan Group of Pictures (GOPs) IBBPBBPBBP 1 3426759108 I PPP GOP

4. Introduction General sequential video coding system 4 2 0 1 3 the average number of frames to be transmitted for randomly accessing an arbitrary frame time … I P P P P

5. Hierarchical Coding Scheme 68104201214591131137 I PPPPPP GOP 7 68 59 10 11 4 3 2 1 012 13 14 time Improve the efficiency of random access operation. (n -> lg n)

6. Center-weighted Hierarchical Coding Scheme 7 68 59 10 11 4 3 2 1 012 13 14 68104 2 0 12 14 59 113 113 7 68104201214591131137 68104201214591131137

7. Center-weighted Hierarchical Coding Scheme e.g. 7 68 59 10 11 4 3 2 1 012 13 14 68104 2 0 12 14 59 113 113 7 x2 Cost : 7 7 6 8 5 9 10 11 4 3 2 1 012 13 14 6 8104 2 0 12 14 5 9 113 11 3 7 Cost : 10 Cost : 8 x3 0213456810121479111213

8. Proximity Approximation Human visual system is normally not very sensitive to minor change of scenes in the temporal domain. (e.g. 0, 3, 6 vs. 0, 4, 6) 7 68 5 9 10 11 4 3 2 1 012 13 14 68104 2 0 12 14 5 9 1 13 11 3 7 Cost : 6 x3

9. Questions in the Hierarchical Structure More overhead while sequential playing The necessity of backward playback? Fast forward speed x3, x5, x7, … are quite similar to x2, x4, x6, … 7 7 3 1 7 3 0 21 7 3 7 3 7 3 3 777711 5 4 5 56 1 2 4 7 9 8 10 13 12 9 13 1011 14 121314 012 021 345 3 67810 4567 1213 891011121314 911 14 time 5 6 6 11 9 9 8 10 13 14 Initial delay & Large buffer

10. Modified Sequential Coding Scheme Add redundant links to sequential coding system 0213456810121479111213 0 02 0246810 468 1214 246810 7 7 3 7 3 5 1 7 3 7 39 11 13 7 11 0 04 48 812 5 9 11 13 7 7 3 7 3 51 77 9 11 9 13 x2x4 time

11. Decoder Error Concealment Recovery of Texture Information Syntax-Based Repair Recovery of Motion Vectors  Set to zero  Use the corresponding MVs in the previous frame  Use the average MVs from spatially adjacent MBs  Use the median MVs from spatially adjacent MBs  Re-estimate the MVs

12. Error Concealment in Hierarchical Coding Structure 68104201214591131137 0213456810121479111213 7 68 59 10 11 4 3 2 1 012 13 14

13. Error Concealment in Hierarchical Coding Structure Add redundant links into the hierarchical tree. 7 68 59 10 11 4 3 2 1 012 13 14 Each damaged leaf node can be recovered via interpolation approach. Each damaged internal node can be reconstructed through its son or the redundant link. ※ Either the redundant link or original link must survive. 68104 2 0 12 14 59 113 113 7

14. Error Concealment in Modified Sequential Coding Structure 0213456810121479111213 XXXX

15. Conclusion and Future Work The proposed video streaming schemes support direct access and error concealment. Future Work  Reduce the buffer size.  Reduce the number of the redundant links.  Reduce the initial waiting time in the hierarchical coding structure.