Content-based rate control for low-bit-rate video applications

In low bit-rate or very low bit-rate video applications, such as videophone and video conferencing, it is difficult for traditional methods to gain a satisfactory image quality. They often suffer from some shortcomings: images with artifacts caused by limited bandwidth and motion discontinuity caused by frame skipping when bit-streams are transmitted through a fixed rate channel in low-delay applications. To attack the two problems above, we propose a content-based rate control method for videophone and video conferencing applications. Our work is focused on three aspects: analysis of bit-streams in low bit-rate video applications, content-based bit allocation to facial areas and background, and low-delay rate control in object-layer. Experiments show that the proposed method can achieve better subjective quality compared with that of the test model TMN5 of H.263, and slightly worse performance in PSNR, but with significantly better subjective quality in the facial areas, compared with that of the TMN8 of H.263+.