Transcoder for converting a first stream to a second stream based on a period conversion factor

摘要

If the number of frames in a GOP of an input stream is not less than 15, the GOP is determined as a control unit time. If the number of frames in the GOP is less than 15, the following GOP is connected thereto until the number of frames becomes not less than 15 and the connected GOPs are determined as a control unit time. After correcting the control unit time, the average input bit rate Sn in each control unit time is obtained, and by using information on the input stream including the average input bit rate Sn, a quantization step value of an output stream is calculated.

主权项

1. A transcoder for converting a first stream into a second stream, comprising:
a period determination part configured to determine a control unit time; a part configured to acquire a bit rate of the first stream per the determined control unit time; a quantization step value calculation part configured to calculate a quantization step value of the second stream by using information on the first stream including the acquired bit rate of the first stream per the control unit time; and a period conversion factor calculation part configured to calculate a period conversion factor αn+1 in a (N+1) period on the basis of
a ratio Tn+1/Sn between a target bit rate T+1 of the second stream in the (N+1)period and a bit rate Sn of the first stream in the N period, using the following equation: αn+1=f(Tn+/Sn), where f(x) is a function of a variable x, ora ratio Tn+1/ASn between the target bit rate Tn+1 of the second stream in the (N+1)period, and an average bit rate ASn of the first stream in a period from a (N−M+1) period, where M is a natural number, through the N period, using the following equation: αn+1=f(Tn+1/ASn), where f (x) is a function of the variable x, wherein said period determination part determines each control unit time so that a ratio of I picture frames included in each control unit time becomes not more than a predetermined ratio, and said quantization step value calculation part includes a part that is configured to calculate the quantization step value of the second stream of the (N+1) period by multiplying a quantization step value of the first stream in the (N+1) period by said period conversion factor.