1. MPEG Video Streaming with VCR Functionality Chia-Wen Lin, Jian Zhou, Jeongnam Youn, Ming-Ting Sun IEEE TRANSACTIONS ON CIRCUITS AND SYSTEMS FOR VIDEO TECHNOLOGY, MARCH 2001

2. Outline Introduction Impacts of VCR Functionality on Decoder Complexity and Network Traffics Supporting Full VCR Functionality with Minimal Network Bandwidth and Decoder Effort Drift Compensation Implementation of an MPEG-4 Video Streaming System with Full VCR Functionality Conclusion

3. Introduction A key technique that enables fast and user friendly browsing of multimedia content is to provide VCR functionality. VCR functionality includes forward, backward, random access, fast-forward/backward. MPEG video compression is based on motion compensated predictive coding with an I-B-P frame structure. We investigate the impacts of the VCR functionality on the network traffic and the video decoder complexity.

4. Introduction(cont.) We propose using reverse-encoded bitstreams at the server to resolve the problem of reverse play. We propose a frame-selection scheme at the server to minimize the required network bandwidth and the decoder complexity. We describe our implementation of an MPEG-4 video streaming system supporting the VCR functionality.

5. Impacts of VCR Functionality on Decoder Complexity and Network Traffics Random Access Fast-Forward Play speed-up factor K = 6

6. Fast-Forward Play We assume the start point of a fast-forward operation is an I-frame, L= gcd( k, N ) After k/L GOPs, the frame to be displayed will again be an I-frame.

10. If N is relatively large compared to k, will grow almost linearly as k increases, thereby leading to a linear increase of the decoding complexity and the network traffics

11. Average number frames and bit-rates for sending the “ Moblie and Calendar ” sequence over network with respect to different speed-up factors in fast-forward play

12. Supporting Full VCR Functionality with Minimal Network Bandwidth and Decoder Effort To solve the problem of the backward- play operation, we propose to add a reverse-encoded bitstream in the server. After we finish the encoding and reach the last frame of the video sequence, we encode the video frames in the reverse order to generate a reverse-encoded bitstream.

13. We arrange the encoding so that the I-frame in the reverse bitstream are interleaved between I-frames in the forward stream. Two metadata files recording the location of the frames in each compressed bitstream are also generated so that the server can switch from the forward-encoded bitstream to the reverse-encoded bitstream.

14. Dual Bitstreams with Least-Cost Frame Selection C R_C : the cost of decoding the next requested P- frame from the current displayed frame. C R_FI : the cost of decoding the next requested P- frame from the closest I-frame in the forward bitstream. C R_RI : the cost of decoding the next requested P- frame from the closest I-frame in the reverse- encoded bitstream. The reference frame to the next requested frame with the least cost will be chosen to initiate the decoding.

15. Example : Fast-backward Speed-up factor=6,the current position is frame 20, which was decoded using the reverse bitstream(R) display sequence : 20,14,8,2 only need to send and decode 6 frames Without least-cost scheme, we need to send and decode 13 frames from the reverse bitstream.

16. Example : Random access The client requests random access to frame 22 when the current decoded frame if frame 3 Only need to send and decode 2 frames Without least-cost scheme, we require 9 frame from frame 14 using the forward bitstream.

17. Performance Analysis of the Proposed Dual-Bitstream Least-Cost Method Random Access Frame N j is the random access point N RI is the position of the I-frame in the reverse bitstream We assume N is even and N RI is odd

19. Fast-forward Play

20. When N and k are coprime(L=1) In fact for the cases that N and k are not coprime, the result of (7) and (8) are still very close.

22. Average number of frames to be sent for decoding a frame and average bit-rates to send “ Moblie and Calendar ” sequence using the proposed method with respect to different speed-up factors

23. Drift Compensation

25. D FR / D RF : a bitstream used for switching from the I- or P-frames of the forward/reverse bitstream to the P- frames of the reverse/forward bitstream Pred(A, B) represents an inter-frame prediction process that frame B is predicted from the reference frame A. D FR n = Pred( F n, R n –1 ) D RF n = Pred( R n, F n +1 )

26. Implementation of an MPEG-4 Video Streaming System with Full VCR Functionality

28. Conclusion Reverse-encoded bitstream to simplify the client machine complexity. Minimum-cost frame-selection scheme to minimize the number of frames needed to be sent over the network and to be decoded. Drift-compensation scheme to limit the drift. An MPEG-4 video streaming system with full VCR functionality can be implemented to minimize the required network bandwidth and decoder complexity.