Patent ID: 9712841
Date: 2017-07-18
CPC Classifications: H04N

Claim:
1. A decoding apparatus which decodes an input bit stream of a coded B frame by adaptively switching, on a block-by-block basis, between frame decoding and field decoding, wherein the input bit stream of the coded B frame is generated by: 1) generating first and second maximum number information indicating a first maximum number of first frame indices and a second maximum number of second frame indices, the first maximum number indicating a maximum number of the first frame index for frame coding and the second maximum number indicating a maximum number of the second frame index for frame coding; 2) generating first commands and second commands, the first commands indicating correspondence between the first frame indices and first reference frames, each of the first frame indices being an index for designating the first reference frame for a current block to be coded and the second commands indicating correspondence between the second frame indices and second reference frames, each of the second frame indices being an index for designating the second reference frame for the current block to be coded; 3) (i) generating a first reference index corresponding to the first reference frame for the current block to be coded and a second reference index corresponding to the second reference frame for the current block to be coded when frame coding is selected for the current block to be coded, the first and second reference frames being referred to when the current block is coded through motion compensation using frame coding, and (ii) generating a first reference index corresponding to the first reference field for the current block to be coded and a second reference index corresponding to the second reference field for the current block to be coded when field coding is selected for the current block to be coded, the first and second reference fields being referred to when the current block is coded through motion compensation using field coding; and 4) coding a prediction error for the current block to be coded, said decoding apparatus comprising: a maximum number obtaining unit operable to obtain, from the input bit stream, the first maximum number of first frame indices and the second maximum number of second frame indices, the first maximum number indicating a maximum number of the first frame index for frame decoding and the second maximum number indicating a maximum number of the second frame index for frame decoding; a command obtaining unit operable to obtain, from the input bit stream, the first commands and the second commands, the first commands indicating correspondence between the first frame indices and first reference frames, each of the first frame indices being an index for designating the first reference frame for a current block to be decoded and the second commands indicating correspondence between the second frame indices and second reference frames, each of the second frame indices being an index for designating the second reference frame for the current block to be decoded; a determining unit operable to determine (i) the maximum number of first field indices for field decoding to be double a value of the first maximum number of the first frame indices and (ii) the maximum number of second field indices for field decoding to be double a value of the second maximum number of the second frame indices; a switching unit operable to adaptively switch, on a block-by-block basis, between frame decoding and field decoding; an extracting unit operable to extract, from the input bit stream, the first reference index and the second reference index for the current block to be decoded; a reference frame/field specifying unit operable to (i) specify the first reference frame corresponding to the extracted first reference index and the second reference frame corresponding to the extracted second reference index when frame decoding is performed for the current block to be decoded, the first and second reference frames being referred to when the current block is decoded through motion compensation using frame decoding, and (ii) specify the first reference field corresponding to the extracted first reference index and the second reference field corresponding to the extracted second reference index when field decoding is performed for the current block to be decoded, the first and second reference fields being referred to when the current block is decoded through motion compensation using field decoding; and a decoding unit operable to decode a prediction error for the current block to be decoded to obtain a recovered current block, wherein said reference frame/field specifying unit further includes: