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 motion vector mapping section for generating a motion vector candidate to be used for each specified segment of the second video coding scheme from the motion vector in the coding parameters of each specified segment of the first video coding scheme; and a coding parameter deciding section for deciding a motion vector to be used in the second video coding scheme from among the generated motion vector candidates in the second video coding scheme according to a prediction error estimation value that estimates a prediction efficiency when using the motion vector candidates and according to a value that estimates a motion vector rate when using the motion vector candidates.