Bit allocation in a coded video sequence

• US 5,835,149 A
• Filed: 06/25/1997
• Issued: 11/10/1998
• Est. Priority Date: 06/06/1995
• Status: Expired due to Fees

• Current Assignee: Intel Corporation
• Original Assignee: Intel Corporation
• Inventors: Astle, Brian
• Primary Examiner(s): AU, AMELIA MEGAN
• Application Number:
  US08/881,932
• Time in Patent Office: 503 Days
• Field of Search: 348/400, 348/403, 348/405, 348/419, 348/420, 348/395, 348/401, 348/404, 348/409, 348/412, 348/415, 382/251, 382/239
• US Class Current: 375/240.05
• CPC Class Codes: H04N 19/107 between spatial and temporal predictive coding, e.g. picture refresh
• CPC Class Codes: H04N 19/114 Adapting the group of pictures [GOP] structure, e.g. number of B-frames between two anchor frames H04N19/107 takes precedence
• CPC Class Codes: H04N 19/115 Selection of the code volume for a coding unit prior to coding
• CPC Class Codes: H04N 19/126 Details of normalisation or weighting functions, e.g. normalisation matrices or variable uniform quantisers
• CPC Class Codes: H04N 19/14 Coding unit complexity, e.g. amount of activity or edge presence estimation H04N19/146 takes precedence
• CPC Class Codes: H04N 19/142 Detection of scene cut or scene change
• CPC Class Codes: H04N 19/146 Data rate or code amount at the encoder output
• CPC Class Codes: H04N 19/149 by estimating the code amount by means of a model, e.g. mathematical model or statistical model
• CPC Class Codes: H04N 19/152 by measuring the fullness of the transmission buffer
• CPC Class Codes: H04N 19/172 the region being a picture, frame or field
• CPC Class Codes: H04N 19/177 the unit being a group of pictures [GOP]
• CPC Class Codes: H04N 19/192 the adaptation method, adaptation tool or adaptation type being iterative or recursive
• CPC Class Codes: H04N 19/59 involving spatial sub-sampling or interpolation, e.g. alteration of picture size or resolution
• CPC Class Codes: H04N 19/61 in combination with predictive coding

Abstract

A computer-implemented method and apparatus for encoding video pictures of a sequence of video pictures, wherein each picture is defined by one picture type of a plurality of picture types and each picture has a complexity. According to a preferred embodiment, the complexity of each picture type is estimated to provide a complexity estimate for each picture type. Encoding a picture at an average quantization level produces an encoded bit stream having a codesize related to the complexity of the picture, and each picture type is associated with a target codesize. An average quantization level is determined for the first picture of each picture type in accordance with the target codesize and complexity estimate of each of the first pictures, respectively. The first picture of each picture type is then encoded at its respective average quantization level. An actual average quantization level at which each first picture was actually encoded is determined, and the complexity estimate for each picture type is updated in accordance with the actual average quantization level and codesize of the first picture of the picture type encoded.

Claims

1. A computer-implemented method for encoding video pictures of a sequence of video pictures, wherein each picture is defined by one picture type of a plurality of picture types and each picture has a complexity, the method comprising the steps of:

(a) providing a complexity estimate for each picture type, wherein encoding a picture at an average quantization level produces an encoded bitstream having a codesize related to the complexity of the picture;

(b) determining an average quantization level for the first picture of each picture type in accordance with a target codesize and complexity estimate of each said first picture, respectively;

(c) encoding the first picture of each picture type at its respective average quantization level;

(d) determining an actual average quantization level at which each first picture was actually encoded in step (c); and

(e) updating the complexity estimate for each picture type in accordance with the actual average quantization level and codesize of the first picture of the picture type encoded in step (c).

2. The method of claim 1, wherein encoding a picture at the average quantization level produces an encoded bitstream having a codesize inversely related to the average quantization level.

3. The method of claim 1, wherein the plurality of picture types comprises intra pictures, predicted pictures, and bidirectional pictures.

4. The method of claim 1, wherein:

the encoded bitstreams are received by a buffer of a hypothetical model decoder which reads the encoded bitstreams from the buffer for decoding the encoded bitstreams; and

the target codesize for each picture is selected in order to avoid underflow and overflow of the buffer.

5. The method of claim 4, wherein:

the target codesize for each picture is selected to achieve a nominal buffer fullness after the encoding of step (c); and

step (b) further comprises the steps of;

(1) comparing the actual buffer fullness achieved after a previous picture was encoded to the nominal buffer fullness for the encoding of the previous picture; and

(2) adjusting the average quantization level in accordance with the comparison of step (b)(1).

6. The method of claim 5, wherein step (b)(2) comprises the step of:

(2) if the actual buffer fullness differs from the nominal buffer fullness by more than a predetermined threshold, then adjusting the average quantization level to obtain nominal buffer fullness within a predetermined number of following pictures.

7. The method of claim 6, wherein the predetermined number of following pictures is ten.

8. The method of claim 6, wherein encoding a picture at the average quantization level produces an encoded bitstream having a codesize inversely related to the average quantization level.

9. The method of claim 6, wherein the plurality of picture types comprises intra pictures, predicted pictures, and bidirectional pictures.

10. An apparatus for encoding video pictures of a sequence of video pictures, wherein each picture is defined by one picture type of a plurality of picture types and each picture has a complexity, the apparatus comprising:

(a) means for providing a complexity estimate for each picture type, wherein encoding a picture at an average quantization level produces an encoded bitstream having a codesize related to the complexity of the picture;

(b) means for determining an average quantization level for the first picture of each picture type in accordance with a target codesize and complexity estimate of each said first picture, respectively;

(c) means for encoding the first picture of each picture type at its respective average quantization level;

(d) means for determining an actual average quantization level at which each first picture was actually encoded by means (c); and

(e) means for updating the complexity estimate for each picture type in accordance with the actual average quantization level and codesize of the first picture of the picture type encoded by means (c).

11. The apparatus of claim 10, wherein encoding a picture at the average quantization level produces an encoded bitstream having a codesize inversely related to the average quantization level.

12. The apparatus of claim 10, wherein the plurality of picture types comprises intra pictures, predicted pictures, and bidirectional pictures.

13. The apparatus of claim 10, wherein:

the encoded bitstreams are received by a buffer of a hypothetical model decoder which reads the encoded bitstreams from the buffer for decoding the encoded bitstreams; and

the target codesize for each picture is selected in order to avoid underflow and overflow of the buffer.

14. The apparatus of claim 13, wherein:

the target codesize for each picture is selected to achieve a nominal buffer fullness after the encoding of means (c); and

means (b) further comprises;

(1) means for comparing the actual buffer fullness achieved after a previous picture was encoded to the nominal buffer fullness for the encoding of the previous picture; and

(2) means for adjusting the average quantization level in accordance with the comparison of means (b)(1).

15. The apparatus of claim 14, wherein means (b)(2) comprises means for adjusting the average quantization level to obtain nominal buffer fullness within a predetermined number of following pictures if the actual buffer fullness differs from the nominal buffer fullness by more than a predetermined threshold.

16. The apparatus of claim 15, wherein the predetermined number of following pictures is ten.

17. The apparatus of claim 15, wherein encoding a picture at the average quantization level produces an encoded bitstream having a codesize inversely related to the average quantization level.

18. The apparatus of claim 15, wherein the plurality of picture types comprises intra pictures, predicted pictures, and bidirectional pictures.

19. The apparatus of claim 15, wherein the apparatus is electrically connected to a bus and the bus is electrically connected to a memory device.

20. The apparatus of claim 10, wherein the apparatus is electrically connected to a bus and the bus is electrically connected to a memory device.

21. A computer-readable medium having stored thereon a plurality of instructions, wherein the plurality of instructions are for encoding video pictures of a sequence of video pictures, wherein each picture is defined by one picture type of a plurality of picture types and each picture has a complexity, and wherein the plurality of instructions, when executed by a processor of a computer system having a storage area, cause the processor to perform the steps of:

(a) providing a complexity estimate for each picture type, wherein encoding a picture at an average quantization level produces an encoded bitstream having a codesize related to the complexity of the picture;

(b) determining an average quantization level for the first picture of each picture type in accordance with a target codesize and complexity estimate of each said first picture, respectively;

(c) encoding the first picture of each picture type at its respective average quantization level;

(d) determining an actual average quantization level at which each first picture was actually encoded in step (c); and

(e) updating the complexity estimate for each picture type in accordance with the actual average quantization level and codesize of the first picture of the picture type encoded in step (c).

22. The computer-readable medium of claim 21, wherein encoding a picture at the average quantization level produces an encoded bitstream having a codesize inversely related to the average quantization level.

23. The computer-readable medium of claim 21, wherein the plurality of picture types comprises intra pictures, predicted pictures, and bidirectional pictures.

24. The computer-readable medium of claim 21, wherein:

the encoded bitstreams are received by a buffer of a hypothetical model decoder which reads the encoded bitstreams from the buffer for decoding the encoded bitstreams; and

the target codesize for each picture is selected in order to avoid underflow and overflow of the buffer.

25. The computer-readable medium of claim 24, wherein:

the target codesize for each picture is selected to achieve a nominal buffer fullness after the encoding of step (c); and

step (b) further comprises the steps of;

(1) comparing the actual buffer fullness achieved after a previous picture was encoded to the nominal buffer fullness for the encoding of the previous picture; and

(2) adjusting the average quantization level in accordance with the comparison of step (b)(1).

26. The computer-readable medium of claim 25, wherein step (b)(2) comprises the step of:

(2) if the actual buffer fullness differs from the nominal buffer fullness by more than a predetermined threshold, then adjusting the average quantization level to obtain nominal buffer fullness within a predetermined number of following pictures.

27. The computer-readable medium of claim 26, wherein the predetermined number of following pictures is ten.

28. The computer-readable medium of claim 26, wherein encoding a picture at the average quantization level produces an encoded bitstream having a codesize inversely related to the average quantization level.

29. The computer-readable medium of claim 26, wherein the plurality of picture types comprises intra pictures, predicted pictures, and bidirectional pictures.