Bit rate control for motion compensated video compression system
View Patent ↗A portion of the number of bits initially allocated for encoding some of the frames of a group of pictures (GOP) is accumulated in a bit bank and is subsequently used to encode other frames that may require a larger number of bits to encode than those initially allocated for these frames. Furthermore, when a scene change P frame is detected in a first GOP, a second GOP is formed. The second GOP includes the scene change P frame as well as the remaining unencoded frames of the original GOP. The P frame of the first GOP is changed to an I frame in the second GOP. Furthermore, the frame to be displayed after the I frame of the second GOP is also changed to a duplicate of the I frame of the second GOP.
1. A method for encoding a video sequence having disposed therein a plurality of frames, the method comprising:
allocating a number of bits for encoding each of the plurality of frames disposed in the video sequence;
selecting a first threshold value;
accumulating a plurality of bits defined by a difference between the allocated number of bits for at least one of the plurality of frames and the first threshold value;
encoding another one of the plurality of frames using at least a portion of the accumulated bits, wherein the plurality of frames is representative of a first group of pictures (GOP), wherein said first GOP comprises at least one frame selected from a group consisting of I-frame, P-frame, and B-frame;
determining whether a P frame of the first GOP includes a scene change;
forming a second GOP that includes the P frame and unencoded frames of the first GOP;
encoding the scene change P frame of the first GOP as an I frame in the second GOP; and
changing a frame that is to be displayed after the I frame of the second GOP to a duplicate of the I frame of the second GOP.
2. The method of claim 1 wherein the at least a portion of the accumulated bits are used when a number of bits required to encode the other one of the plurality of frames exceeds the first threshold value.
3. The method of claim 1 wherein the other one of the plurality of frames is a scene change frame.
4. The method of claim 1 further comprising:
maintaining the accumulated plurality of bits at a level equal to a second threshold value.
5. The method of claim 4 wherein said second threshold value is related to a variable that is defined by a total number of bits allocated for the frames of the first GOP.
6. The method of claim 5 wherein said variable is further defined by a weighted function of relative number of bits used to encode each of I, P and B frames of the first GOP.
7. The method of claim 1 wherein the first threshold value is selected in accordance with the at least one of the plurality of frames.
8. The method of claim 1 further comprising:
receiving the second GOP; and
encoding at least one of the frames of the second GOP using the bits accumulated from the frames of the first GOP.
9. The method of claim 1 wherein a count of the accumulated bits is maintained in a counter.
10. The method of claim 1 wherein the at least one of the plurality of frames not including a scene change.
11. A system for encoding a video sequence having disposed therein a plurality of frames, the system comprising:
a module for allocating a number of bits for encoding each of the plurality of frames disposed in the video sequence;
a module for accumulating a plurality of bits defined by a difference between the allocated number of bits for at least one of the plurality of frames and a first threshold value;
a module for encoding another one of the plurality of frames using at least a portion of the accumulated bits, wherein the plurality of frames is representative of a first group of pictures (GOP), wherein said first GOP comprises at least one frame selected from a group consisting of I-frame, P-frame, and B-frame;
a module for determining whether a P frame of the GOP includes a scene change;
a module for forming a second GOP that includes the P frame and unencoded frames of the first GOP;
a module for encoding the scene change P frame of the first GOP as an I frame in the second GOP; and
a module for changing a frame that is to be displayed after the I frame of the second GOP to a duplicate of the I frame of the second GOP.
12. The system of claim 11 wherein the at least a portion of the accumulated bits are used when a number of bits required to encode the other one of the plurality of frames exceeds the first threshold value.
13. The system of claim 11 wherein the other one of the plurality of frames is a scene change frame.
14. The system of claim 11 further comprising:
a module for maintaining the accumulated plurality of bits at a level equal to a second threshold value.
15. The system of claim 11 wherein the first threshold value is selected in accordance with the at least one of the plurality of frames.
16. The system of claim 11 further comprising:
a module for encoding at least one frame of the second GOP using the bits accumulated from the frames of the first GOP.
17. The system of claim 11 wherein each of the respective modules is one of a software module and a hardware module.
18. The system of claim 11 wherein each of the respective modules includes both software and hardware modules.
19. The system of claim 11 further comprising a counter for maintaining a count of the accumulated bits.
20. The system of claim 11 wherein the at least one of the plurality of frames not including a scene change.