Method and apparatus for encoding video, method and apparatus for decoding video, and programs therefor

A video encoding apparatus using fractional-accuracy motion compensation, the apparatus comprising:

• a motion vector acquisition unit which performs a motion search to acquire a motion vector;
• a reference probability calculation unit which calculates reference probabilities at fractional-pixel positions designated by the acquired motion vector;
• a grouping unit which divides interpolation positions which are the fractional-pixel positions into multiple groups based on the calculated reference probabilities;
• an interpolation filter coefficient selection unit which selects, for each of the groups of the interpolation positions, interpolation filter coefficients to be used for generating an interpolated prediction picture from among multiple interpolation filter coefficient candidates;
• a first encoding unit which generates the interpolated prediction picture using the selected interpolation filter coefficients and performs encoding with the fractional-accuracy motion compensation based on the interpolated prediction picture, for each of the groups of the interpolation positions;
• and
• a second encoding unit which encodes information indicating grouping of the interpolation positions and information indicating interpolation filter coefficients to be used for each of the groups of the interpolation positions.

A video decoding method using fractional-accuracy motion compensation, the method comprising:

• a step of decoding information indicating grouping of interpolation positions which are fractional-pixel positions and information indicating interpolation filter coefficients to be used for each of groups of interpolation positions;
• a step of determining, for each of the groups of the interpolation positions, interpolation filter coefficient to be used for generating an interpolated prediction picture based on the decoded information;
• a step of decoding a motion vector and a prediction residual signal;
• a step of generating the interpolated prediction picture using an interpolation filter determined by the determined interpolation filter coefficients and generating a prediction signal in motion compensation;
• and
• a step of generating a decoded picture using the decoded prediction residual signal and the generated prediction signal.

A video decoding apparatus using fractional-accuracy motion compensation, the apparatus comprising:

• a first decoding unit which decodes information indicating grouping of interpolation positions which are fractional-pixel positions and information indicating interpolation filter coefficients to be used for each of groups of interpolation positions;
• an interpolation filter coefficient determination unit which determines, for each of the groups of the interpolation positions, interpolation filter coefficients to be used for generating an interpolated prediction picture based on the decoded information;
• a second decoding unit which decodes a motion vector and a prediction residual signal;
• a prediction signal generation unit which generates the interpolated prediction picture using an interpolation filter determined by the determined interpolation filter coefficients, and generates a prediction signal in motion compensation;
• and
• a decoded picture generation unit which generates a decoded picture using the decoded prediction residual signal and the generated prediction signal.