Apparatus and method for adaptive rate in video transcoder

PURPOSE: A device for controlling an adaptive bit rate of a video transcoder is provided to suggest logarithmic R-Q characteristics, and to adaptively change a parameter compensating for a difference between MPEG-1 coding efficiency and MPEG-4 coding efficiency, without fixing the parameter to a specific value, thereby generating an exact MPEG-4 quantization parameter. CONSTITUTION: A logarithmic R-Q modeling portion(100) applies a logarithmic R-Q model adaptively obtained according to image characteristics to an MPEG-1 quantization parameter, and outputs a quantization parameter of a target MPEG-1. A quantization parameter controller(120) applies a variable parameter to the outputted quantization parameter according to the image characteristics, and calculates a controlled quantization parameter. A quantization parameter determiner(140) applies a gradual access function to the controlled quantization parameter, and generates a final quantization parameter for MPEG-4. A bit amount calculator(160) calculates a bit amount difference between screens of the target MPEG-1 and the outputted MPEG-4, and feeds back the bit amount difference to the logarithmic R-Q modeling portion(100).