Research

Video Compression for Lossy Packet Networks with Mode Switching and a Dual Frame Buffer Video codecs that use motion compensation benefit greatly from the development of algorithms for near-optimal intra/inter mode switching within a rate-distortion framework. A separate development has involved the use of multiple-frame prediction, in which more than one past reference frame is available for motion estimation. In this paper, we show that using a dual-frame buffer (one short-term frame and one long-term frame available for prediction) together with intra/inter mode switching improves the compression performance of the coder. We improve the mode-switching algorithm with the use of half-pel motion vectors. In addition, we investigate the effect of feedback in making more informed and effective mode-switching decisions. Feedback information is used to limit drift errors due to packet losses by synchronizing the long-term frame buffers of both the encoder and the decoder.

Optimal Mode Selection for a Pulsed-Quality Dual-Frame Video Coder A dual-frame video coder employs two past reference frames for motion compensated prediction. Compared to conventional single frame prediction, the dual-frame encoder can have advantages both in distortion-rate performance and in error resilience. In previous work, it was shown that optimal mode selection can enhance the performance of a dual-frame encoder. In another strand of previous work, it was shown that uneven assignment of quality to frames, to create high-quality (HQ) long-term reference frames, can enhance the performance of a dual-frame encoder. In this letter, we combine these two strands and demonstrate the performance advantages of optimal mode selection among HQ frames for video transmission over noisy channels.

Drift-Resistant SNR Scalable Video Coding We address the problem of enhancement layer drift estimation for fine granular scalable video. An optimal per-pixel drift estimation algorithm is introduced. The encoder assumes that there is some truncation of the enhancement layer, which does not allow the enhancement layer reference to be properly reconstructed, and the encoder recursively estimates the associated drift and chooses coding modes accordingly. The approach yields performance gains of about 1dB across low to medium rates. In addition, we investigate dual frame prediction, for both base and enhancement layer, with pulsed quality allocation in the base layer.

Quality Evaluation of Motion-Compensated Edge Artifacts in Compressed Video Little attention has been paid to an impairment common in motion-compensated video compression: the addition of high frequency (HF) energy as motion compensation displaces blocking artifacts off block boundaries. In this paper, we employ an energy-based approach to measure this motion-compensated edge artifact, using both compressed bitstream information and decoded pixels. We evaluate the performance of our proposed metric, along with several blocking and blurring metrics, on compressed video in two ways. First, ordinal scales are evaluated through a series of expectations that a good quality metric should satisfy: the objective evaluation. Then the best performing metrics are subjectively evaluated. The same subjective data set is finally used to obtain interval scales to gain more insight. Experimental results show that we accurately estimate the percentage of the added HF energy in compressed video.

Ongoing Research (a) Delay Constraints for Hierarchical B-Pictures in H.264/AVC (b) Flicker Artifact Suppression for Wavelet-based Intra Frame Coders

Back to Home