In this paper, we propose an adaptive video frame rate control method, called AFCON, that video encoders use in conjunction with explicit rate based congestion control in the network. First, an encoder buffer constraint which guarantees the end-to-end delay of video frames is derived under the assumption of bounded network transmission delay for every frame data. AFCON is based on the constraint and consists of future channel rate prediction, frame discarding, and frame skipping. Recursive Least-Squares (RLS) is used to predict the low-frequency component of the channel rate. Frame discarding prevents the delay violation of frames due to the prediction error of the channel rate. Frame skipping adapts the encoder output rate to the channel rate while avoiding abrupt quality degradation during the congestion period. From the simulation results, it is shown that AFCON can adapt to the time-varying rate channel with less degradation in temporal resolution and in PSNR performance compared to the conventional approach.

Practical and accurate R-Q (rate-quantization) and D-Q (distortion-quantization) models are presented to describe the R-D (rate-distortion) relationship before encoding a frame. The R-Q model is based on a linear relationship between non-zero level count of the DCT coefficients and the generated bits, while the D-Q model comes from the observation that the ratio QP2/D(QP) can be very accurately approximated by a quadratic function of QP, where QP is the quantization parameter used for quantization of DCT coefficients in H. 263 video coding standard. Simulation results show that the proposed models estimate the real coding results very accurately.