Patent ID: 7330509

Claim:
A method of transcoding an input compressed signal stream to an output compressed signal stream, the signal stream being a video stream compressed pursuant to the standards of the Moving Picture Experts Group (MPEG), and within a Group of Pictures (GOP) three types of pictures are distinguished according to a compression method used: Intra-mode pictures (I pictures) which are compressed independently of any other picture, Predictively motion-compensated pictures (P pictures) which are reconstructed from the compressed data in that picture and two most recently reconstructed fields from previously displayed I or P pictures, and Bidirectionally motion-compensated pictures (B pictures) which are reconstructed from the compressed data in that picture plus two reconstructed fields from previously displayed I or P pictures and two reconstructed fields from I or P pictures that will be displayed in the future, said method comprising: performing adaptive frame rate transcoding for a sub-GOP (Group of Pictures), said sub-GOP comprising one or more types of pictures of said input compressed signal stream to be transcoded, said performing including: determining whether a picture is an I picture, a B picture or a P picture type from the picture header information; transcoding all I pictures; and if a series of pictures comprises a (B, P) pair, which starts with a B picture, may have zero, one or more intermediate B pictures, and ends with a P picture, applying adaptive picture rate transcoding with joint temporal-spatial rate control to the series of pictures of the (B, P) pair.