Patent attributes
Conventionally, there has been a case that the direct mode cannot be applied effectively depending on the block. With such being the case, information indicating whether a backward reference frame set by default can be utilized in the direct mode is provided to a decoder. A switching procedure to switch to a compensation method applicable when a collocated block has no forward motion vector for effective use, and the compensation method are also provided to the decoder. Thus, it is possible to clearly determine whether the reference frame can be used in the direct mode. Further, when the frame number has no time information, it is possible to effectively send information indicating the relationship between the reference frame and the current frame. Furthermore, the alternative mode and its switching procedure of the present invention make it possible to improve the prediction performance when the direct mode cannot be applied.
