Encoding Stored Video for Streaming Applications IEEE TRANSACTIONS ON CIRCUITS AND SYSTEMS FOR VIDEO TECHNOLOGY, VOL. 11, NO. 2, FEBRUARY 2001 I.-Ming Pao Ming-Ting Sun Outline Introduction Method Simulation Result Conclusion Introduction Digital video applications have become increasingly popular. There are several video standards established for different purposes. e.g, MPEG-1, MPEG-2, H.263… Introduction Basic building blocks Introduction Real-time Visual Communication delay sensitive processes need to be done in constraint time rate control scheme is not suitable Nonreal-time Visual Communication delay tolerable pre-loaded time decoder buffer rate control scheme is suitable Buffer and Pre-loading Introduction Streaming video applications Video sequences are encoded off-line Stored in a server Pre-load before playback e.g, VOD Problem Bit allocation and video quality Minimum distortion under the rate constraint Introduction Contribution of this paper : 1. Propose a sliding-window rate-control scheme. 2. A quantized DCT coefficient selection scheme. 3. Improve video quality for video streaming. Outline Introduction Method Simulation Result Conclusion Global View Generate encoded bitstream Sliding-window encoding scheme Consider the constraints buffer-size pre-loading time DCT coefficient selection Run-length coding Sliding-Window Encoding Scheme Use future frames to improve video quality. Set window size W to encode video frame. frames : i, i+1, …, i+W-1 let frame i be the current frame This proposed encoder better than real-time’s for the same bitrate[20]. [20] I.-M. Pao and M.-T. Sun, “A rate-control scheme for streaming video encoding,”in Proc. 32nd Asilomar Conf. Signals, Systems and Computers, vol. 2, Asilomar, CA, Nov. 1998, pp. 1616–1620. Sliding-Window Encoding Scheme Bit allocation rate and distortion scheme[18] low distortion or high-rate case high distortion or low-rate case [18] J. Ribas-Corbera and S. Lei, “Rate control in DCT video coding for low-delay video communications,” IEEE Trans. Circuits Syst. Video Technol., vol. 9, pp. 172–185, Feb. 1999. Sliding-Window Encoding Scheme Bit allocation mathematical modeling[18] [18] J. Ribas-Corbera and S. Lei, “Rate control in DCT video coding for low-delay video communications,” IEEE Trans. Circuits Syst. Video Technol., vol. 9, pp. 172–185, Feb. 1999. Sliding-Window Encoding Scheme Target number of bits for encoding frame R × time Buffer-size and Pre-loading Time Requirement Why need buffer ? store the excess bits waiting to be decoded e.g, bits of future frames Why need pre-loading time? the delay before playback Buffer-size and Pre-loading Time Requirement Buffer variation expression : Buffer Size G B0 p0 Buffer-size and Pre-loading Time Requirement A. Finding decoder buffer size and pre-loading time given a video bitstream overflow underflow Buffer-size and Pre-loading Time Requirement B. Generating a video bitstream given decoder buffer size and pre-loading time To prevent the buffer-underflow : To prevent the buffer-overflow : Bit Allocation with Constraints Step 0 : Initialization : initialize the bit-count regulator . Step 1 : Compute the Proposed Target Bits for Frame : compute the ideal target number of bits for frame i (i = 0, 1, 2, 3, ...). avoid the underflow and overflow constraints. Bit Allocation with Constraints Step 2 : Macroblock-Layer Rate-Control : distribute to the macroblocks in the ith frame. find DCT coefficient selection for each macroblock. encode bitstream Step 3 : Update Bit-Count Regulator : update regulator : if there are more frames to be encoded, go to Step 1, or else stop. DCT Coefficient Selection Quantize the DCT coefficients rate-distortion sense and macroblock level. quantizer step-sizes(Q) largely determine the ratedistortion tradeoff. DCT Coefficient Selection Run-length coding with LAST (LAST, RUN, LEVEL) (0, 4, 6) bitstream DCT Coefficient Selection There are not optimal for all video sequences by limited quantizer selections and predetermined run-length codeword. The encoder can adjust the quantized coefficient’s level. a marginal distortion increase but a significant bit-rate reduction. DCT Coefficient Selection This paper use Lagrange multiplier method for rate-distortion optimization in selecting the quantization parameter (QP) and adjusting the quantized DCT coefficients (LEVEL). the best combination of QP and LEVELs will be the lowest cost in the rate-distortion sense. DCT Coefficient Selection Goal is to find the minimum distortion under the rate constraint : for every 8 X 8 block the optimal QP for the macroblock the LEVEL for each coefficient DCT Coefficient Selection The constrained problem converts to an unconstrained problem through the Lagrange multiplier λ (≥ 0). . the problem becomes the determination of the LEVELs of the coefficients. Better Outline Introduction Method Simulation Result Conclusion Simulation Result Different bitrates : 32, 64, and 128 kbits/s Different types of video sequences : large facial movement head and shoulder camera panning Compare with TMN8 Outline Introduction Method Simulation Result Conclusion Conclusion Better video quality than TMN8 in high motion-activity frames and scene-change frames. Require more buffer size and pre-loading time than TMN8.