| 摘要 |
A system for rate control during transcoding and encoding of digital video data in a multi-program transmission environment accommodates changes in the GOP structure of any of the programs, e.g., due to a commercial insertion or the like. A hierarchical bit allocation scheme is used, where bits are allocated on a super group of pictures (GOP) level, i.e., a grouping of multiple GOPs, a super frame level, and an individual frame level. The bit allocation for the super GOP and each picture is adjusted when a change in the structure of a group of pictures (GOP) is detected for any of the pre-compressed programs. The super GOP length may also be adjusted if required to maintain an integer number of GOPs therein. A change in the GOP structure is detected based on a change in the GOP length or sub_GOP length (distance between P pictures). For pre-compressed data, initial GOP lengths and sub_GOP lengths can be assumed and adjusted as required based on actual measurements. For a current I or P picture, the sub GOP length is calculated based on temporal references of the current picture and a previous I or P picture. For a current B picture, the same calculation is used, plus one picture. |
