Transcoder for converting a first stream into a second stream using an area specification function and a relation determining function

摘要

A technique for suppressing a significant variation of a quantization step value and enabling a stable rate control to be performed. A function is used for calculating a quantization step conversion factor from a bit rate ratio is a straight line with an inclination of -1, intersecting a function at a reference point. The function is a monotone decreasing exponential function. A reference bit rate ratio (R0) is expressed as R0=T/S by using a total bit rate (S) of a first stream and a total target bit rate (T) of a second stream. The function appropriately represents a relation between the bit rate ratio and the quantization step conversion factor in coding conversion but has a large rate of variation in an area where the bit rate ratio is about 0.5. The function has a small rate of variation and can suppress a significant variation of the quantization step conversion value.