Rate control for an MPEG transcoder without a priori knowledge picture type

An apparatus for allocating bits for coding a sequence of pictures in a bitstream received at a digital video transcoder, comprising:

• (a) means for providing an assumed length N′ of a particular group of pictures (GOP) of said bitstream;
• (b) means for providing an assumed bit budget as a function of said assumed length N′;
• (c) means for allocating bits for coding a first picture of said particular GOP in accordance with said assumed bit budget;
• (d) means for determining a picture type of a second picture that immediately follows said first picture;
• (e) means for adjusting said assumed bit budget according to said picture type of said second picture;
• and
• (f) means for allocating bits for coding said second picture in accordance with said adjusted bit budget.

A method for allocating bits for coding a sequence of pictures in a bitstream received at a digital video transcoder, comprising the steps of:

• (a) providing a length of groups of pictures (GOPs) of said bitstream;
• (b) providing a distance between each I-picture and a next successive P-picture in said GOPs;
• (c) maintaining a count of a number of remaining I-, P- and B-pictures, respectively, in each GOP as each picture in said GOPs is coded;
• (d) providing an assumed bit budget in response to said steps (a), (b) and (c) for coding pictures in said GOPs;
• (e) verifying, and adjusting, if necessary, said length after each I-picture in said GOPs is coded;
• (f) verifying, and adjusting, if necessary, said distance after each I-picture and/or P-picture in said GOPs is coded;
• (g) verifying, and adjusting, if necessary, the count of the number of remaining I-, P- and B-pictures, in response to said steps (e) and (f);
• and
• (g) adjusting, if necessary, said assumed bit budget in response to said steps (e), (f) and (g).

An apparatus for allocating bits for coding a sequence of pictures in a bitstream received at a digital video transcoder, comprising:

• (a) means for providing a length of groups of pictures (GOPs) of said bitstream;
• (b) means for providing a distance between each I-picture and a next successive P-picture in said GOPs;
• (c) means for maintaining a count of a number of remaining I-, P- and B-pictures, respectively, in each GOP as each picture in said GOPs is coded;
• (d) means for providing an assumed bit budget in response to said means (a), (b) and (c) for coding pictures in said GOPs;
• (e) means for verifying, and adjusting, if necessary, said length after each I-picture in said GOPs is coded;
• (f) means for verifying, and adjusting, if necessary, said distance after each I-picture and/or P-picture in said GOPs is coded;
• (g) means for verifying, and adjusting, if necessary, the count of the number of remaining I-, P- and B-pictures, in response to said means (e) and (f);
• and
• (g) means for adjusting, if necessary, said assumed bit budget in response to said means (e), (f) and (g).