Improved low bit-rate MPEG-4 video coding with spatio-temporal rate control

In the case of a video delivery system which is constructed by a constant bit-rate channel, the encoder must send a constant number of bits per unit time period. Therefore, the number of bits used in encoding must be regulated by the rate control algorithm. Basically, the rate control of a video signal such as MPEG-4 is realized by adaptive quantization. However, since adaptive quantization has the limitation of bit regulation, temporal resolution conversion is also introduced. The temporal resolution conversion is effective for decreasing the number of bits for encoding, however the conversion causes a decrease in temporal resolution. Decreasing the temporal resolution results in jerky degradation. In this paper, in order to keep the temporal resolution, we introduce the spatial resolution conversion for rate control algorithm. Moreover, we show how to choose the temporal resolution conversion or the spatial resolution. Thus, the proposed method realizes low bit-rate video coding while preserving the original frame-rate.