MPEG-4 codec 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. Temporal resolution conversion is effective for decreasing the number of bits for encoding; however, the conversion causes a decrease in temporal resolution. Decreasing temporal resolution becomes a jerky degradation. In order to keep the temporal resolution, we introduce spatial resolution conversion for the rate control algorithm. Moreover, we show how to choose temporal resolution conversion or spatial resolution conversion. Thus, the proposed method realizes low bit-rate video coding while preserving the original frame-rate.