Method and a apparatus for controlling a bit rate of picture data, and a storage medium which stores a program for controlling the bit rate

In order to prevent a deterioration in reproduction quality of a moving picture, which is caused by a difference in data transfer rate for each frame of the moving picture data, when compressing the picture data, a bit rate of the compressed data is predicted, thus deriving a prediction value of the data transfer rate after the compression. The compression is performed by modifying the picture so that the prediction value falls within a range which is suitable for a data transfer rate set in advance. The modification of the picture data is performed by writing a pattern for the adjustment into frames of the original picture.