Rate control for digital video compression processing
View Patent ↗A video compression algorithm for converting a digital video stream having video content into a compressed video bitstream, includes rate control to control the size of the compressed video bitstream. The rate control takes into account two or more of (1) detected scene changes, (2) detected repeated fields resulting from inverse telecine processing, (3) characterized video content complexity, and (4) a determined level of a model of a bit buffer associated with a decoder adapted to decode the compressed video bitstream. In preferred embodiments, the rate control takes into account two or more of these four factors in an integrated manner to change the allocation of bits for encoding different portions of the video stream.
1. A method comprising applying a video compression algorithm by a circuit to a digital video stream having video content to generate a compressed video bitstream, wherein:
the video compression algorithm includes rate control adapted to control size of the compressed video bitstream; and
the rate control takes into account two or more of (1) detected scene changes, (2) detected repeated fields resulting from inverse telecine processing, (3) characterized video content complexity, and (4) a determined level of a model of a bit buffer associated with a decoder adapted to decode the compressed video bitstream; and
wherein the rate control allocates additional bits for encoding a repeated field and a determined bit buffer model level that corresponds to storing at least one byte.
2. The invention of claim 1 , wherein the rate control changes allocation of bits for encoding different portions of the video stream having particular combinations of characteristics associated with one of (1) the detected scene changes, and (2) the characterized video content complexity.
3. The invention of claim 2 , wherein the rate control allocates additional bits for encoding a portion of the video stream if the portion is both associated with a detected scene change and associated with a determined bit buffer model level that corresponds to storing at least one byte.
4. The invention of claim 2 , wherein the rate control allocates additional bits for encoding a portion of the video stream if the portion is associated with a determined bit buffer model level that corresponds to storing at least one byte associated with decreasing characterized video content complexity.
5. The invention of claim 1 , wherein:
the rate control takes into account (1) the detected scene changes, (2) the detected repeated fields, (3) the characterized video content complexity, and (4) the determined bit buffer model level;
the method comprises:
analyzing the video stream to detect scene changes in the video content;
analyzing the video stream to detect repeated fields resulting from the inverse telecine processing;
analyzing the video stream to characterize complexity of the video content;
and maintaining the model of the bit buffer associated with the decoder for the compressed video bitstream to determine bit buffer model level.
6. The invention of claim 5 , wherein the rate control changes allocation of bits for encoding different portions of the video stream having particular combinations of characteristics associated with two or more of (1) the detected scene changes, (2) the detected repeated fields, (3) the characterized video content complexity, and (4) the determined bit buffer model level.
7. The invention of claim 5 , wherein, if a scene change is detected, then the analysis of the video stream for repeated fields is reset.
8. The invention of claim 5 , wherein:
the rate control allocates additional bits to encode a portion of the video stream if the portion is:
(1) both (i) associated with a detected repeated field and (ii) associated with a determined bit buffer model level that corresponds to storing at least one byte; or
(2) both (i) associated with a detected scene change and (ii) associated with a determined bit buffer model level that corresponds to storing at least one byte.
9. The invention of claim 8 , wherein the rate control allocates fewer bits to encode the portion of the video stream if the portion is associated with a determined bit buffer model level that does correspond to an underflow condition.
10. The invention of claim 8 , wherein the rate control adds padding bits to encode the portion of the video stream if the portion is associated with a determined bit buffer model level that corresponds to an overflow condition.
11. The invention of claim 5 , wherein the bit buffer model level is increased more for portions of the video stream associated with the detected repeated fields than for portions of the video stream not associated with the detected repeated fields.
12. The invention of claim 1 , wherein the rate control selects quantization levels used to quantize DCT coefficients corresponding to DCT-transformed pixel data to control the size of the compressed video bitstream.
13. The invention of claim 12 , wherein, if a non-zero quantized DCT coefficient is less than a specified threshold, then the quantized DCT coefficient is set to zero.
14. The invention of claim 13 , wherein the magnitude of the specified threshold is a function of the determined bit buffer model level.
15. The invention of claim 12 , wherein the selection of quantization levels is a function of the determined bit buffer model level.
16. The invention of claim 15 , wherein:
the quantization level for each macroblock is selected based on a function that includes a bias term;
and the bias term is a function of the determined bit buffer model level.
17. The invention of claim 1 , wherein the compressed video bitstream conforms to an MPEG video compression standard.
18. The invention of claim 17 , wherein the MPEG video compression standard is MPEG2.
19. A video encoder for applying a video compression algorithm to a digital video stream having video content to generate a compressed video bitstream, wherein:
the video compression algorithm includes rate control adapted to control size of the compressed video bitstream;
and the rate control takes into account two or more of (1) detected scene changes, (2) detected repeated fields resulting from inverse telecine processing, (3) characterized video content complexity, and (4) a determined level of a model of a bit buffer associated with a decoder adapted to decode the compressed video bitstream; said video encoder further comprising:
a circuit for generating a plurality of indicators indicative of differences between a plurality of slices in a field and a corresponding plurality of slices in another field.
20. A computer-readable medium, having encoded thereon program code, wherein, when the program code is executed by a machine, the machine implements a method comprising applying a video compression algorithm to a digital video stream having video content to generate a compressed video bitstream, wherein:
the video compression algorithm includes rate control adapted to control size of the compressed video bitstream;
and the rate control takes into account two or more of (1) detected scene changes, (2) detected repeated fields resulting from inverse telecine processing, (3) characterized video content complexity, and (4) a determined level of a model of a bit buffer associated with a decoder adapted to decode the compressed video bitstream; and
wherein a plurality of indicators indicative of differences between a plurality of slices in a field and a corresponding plurality of slices in another field are generated.
21. A computer-readable medium, having encoded thereon a compressed video bitstream generated by applying a video compression algorithm to a digital video stream having video content, wherein:
the video compression algorithm includes rate control adapted to control size of the compressed video bitstream;
and the rate control takes into account two or more of (1) detected scene changes, (2) detected repeated fields resulting from inverse telecine processing, (3) characterized video content complexity, and (4) a determined level of a model of a bit buffer associated with a decoder adapted to decode the compressed video bitstream; and
a plurality of indicators indicative of differences between a plurality of slices in a field and another field are generated.
22. The video encoder of claim 19 , wherein scene changes are detected based on the plurality of indicators.
23. The video encoder of claim 22 , wherein a scene change is detected if a portion of the plurality of the indicators exceeding a predetermined threshold correspond to slices covering an area of the field exceeding another predetermined threshold.
24. The video encoder of claim 19 , wherein repeated fields are detected based on the plurality of indicators.
25. The video encoder of claim 24 , wherein repeated fields are detected if a portion of the plurality of indicators less than a predetermined threshold correspond to slices covering an area of the field exceeding another predetermined threshold.
26. The invention of claim 5 , further comprising:
generating a plurality of indicators indicative of differences between a plurality of slices in a field and another field; and wherein
analyzing the video stream to detect scene changes in the video content further comprises:
detecting a scene change if a portion of the plurality of the indicators exceeding a predetermined threshold correspond to slices covering an area of the field exceeding another predetermined threshold; and
wherein analyzing the video stream to detect repeated fields resulting from the inverse telecine processing further comprises:
wherein repeated fields are detected if a portion of the plurality of indicators less than a predetermined threshold correspond to slices covering an area of the field exceeding another predetermined threshold.