Transcoder, recorder, and transcoding method

A transcoder for decoding a motion picture stream encoded by using a first coding scheme, which provides intraframe coding and interframe predictive coding, and encoding the decoded motion picture stream by using a second coding scheme, the transcoder comprising:

• a decoder for decoding an input motion picture stream and detecting sub-information indicating whether an intraframe coding scheme or an interframe predictive coding scheme is used, wherein the sub-information is attached to each decoding process unit within a frame;
• and
• an encoder for changing the order of searching for the frame to be referenced at the time of coding depending on whether the sub-information indicates the use of the intraframe coding scheme or the interframe predictive coding scheme,
• wherein a reference frame for motion compensation can be selected from a plurality of decoded frames in units of an encoding process unit in the second coding scheme,
• when a frame to be encoded in the second coding scheme used interframe predictive coding scheme in the first coding scheme and the sub-information attached to an encoding process unit within the frame to be encoded indicates the use of the intraframe coding scheme, a decoded frame which was not referenced in the first coding scheme is searched for as the reference frame for the encoding process unit in the second coding scheme.

A transcoding method for decoding a motion picture stream encoded by using a first coding scheme, which provides intraframe coding and interframe predictive coding, and encoding the decoded motion picture stream by using a second coding scheme, wherein:

• a frame to be decoded is provided with sub-information that indicates whether an intraframe coding scheme or an interframe predictive coding scheme is used, wherein the sub-information is attached to each decoding process unit within the frame;
• and
• the frame to be referenced at the time of coding, changes depending on whether the sub-information indicates the use of the intraframe coding scheme or the interframe predictive coding scheme,
• wherein a reference frame for motion compensation can be selected from a plurality of decoded frames in units of an encoding process unit in the second coding scheme,
• when a frame to be encoded in the second coding scheme used interframe predictive coding scheme in the first coding scheme and the sub-information attached to an encoding process unit within the frame to be encoded indicates the use of the intraframe coding scheme, a decoded frame which was not referenced in the first coding scheme is selected as the reference frame for the encoding process unit in the second coding scheme.