1. A video data converter for converting input video coded data based on a first video coding scheme to video coded data based on a second video coding scheme, said first video coding scheme carrying out coding by dividing each frame of a video signal into specified segments and by selecting coding parameters including a motion vector for each specified segment, and said second video coding scheme carrying out coding by dividing each frame of the video signal into specified segments and by selecting coding parameters for each specified segment, said video data converter comprising: a decoder for decoding from the input video coded data a video signal coded according to the first video coding scheme; a motion vector mapping section for generating a plurality of motion vector candidates for each specified segment of a frame of the decoded video signal to be coded according to the second video coding scheme, the plurality of motion vector candidates being generated from the motion vector in the coding parameters of each specified segment of the corresponding frame of the video signal coded according to the first video coding scheme; and a coding parameter deciding section for selecting for each of the specified segments a motion vector to be used in the second video coding scheme from among the generated motion vector candidates, the motion vector being selected according to a prediction error estimation value that estimates a prediction efficiency when using each of the motion vector candidates and according to a motion vector rate estimation value that estimates a motion vector rate when using each of the motion vector candidates.