CCITT H.261 compatible mixed bit rate coding of video for ATM networks

A mixed bit rate (MBR) video coding method is presented for asynchronous transfer mode (ATM) networks which has communication compatibility between constant bit rate (CBR) video codecs and variable bit rate (VBR) codecs. In MBR video coding, essential information is encoded at a CBR by using a conventional CBR coding method such as H.261 and enhancement information is encoded at a VBR to attain constant image quality. To realize the MBR coding of video, the conventional embedded pulse code modulation (PCM) quantization is extended by applying the requantization method only to the least significant bit (LSB) of the quantizer output. In the EX-EMB PCM method, the most significant part and least significant part (MSP/LSP) separation of embedded PCM and an additional threshold for the requantizer are dynamically determined to attain a desired distortion. The MBR codec with EX-EMB PCM was evaluated by computer simulations. The simulation results showed that the proposed method was effective not only for improving video quality but also it prevented the degradations of image quality at the scene change by increasing the bit rate for the VBR channel