A bit rate transcoding method includes: (a) receiving a motion vector of a current macroblock (MB); (b) retrieving an error count of a referenced previous MB for setting it as the error count of the current MB; (c) calculating a weight value; (d) calculating a new quantization parameter, and multiplying the same by the weight value so as to obtain a weighted new quantization parameter falling into a continuous distribution; (e) selectively using a transformation technique to transform the weighted new quantization parameter into one falling into a discrete distribution; (f) if the weighted new quantization parameter exhibits the continuous distribution, and if the weighted new quantization parameter is within a predetermined range, incrementing the error count by a predetermined value; and (g) if the weighted new quantization parameter exhibits the discrete distribution, and if the weighted new quantization parameter does not belong to a smallest quantization parameter cluster, incrementing the error count by a predetermined value.