Computing collocated macroblock information for direct mode macroblocks

• US 20090003446A1
• Filed: 06/30/2007
• Published: 01/01/2009
• Est. Priority Date: 06/30/2007
• Status: Active Grant

• Current Assignee: Microsoft Technology Licensing LLC (Microsoft Corporation)
• Original Assignee: Microsoft Corporation
• Inventors: Chen, William, Wu, Yongjun, Zhao, Weidong
• Granted Patent: US 8,254,455 B2
• Time in Patent Office: Days
• US Class Current: 375/240.160
• CPC Class Codes: H04N 19/117 Filters, e.g. for pre-processing or post-processing sub-band filter banks H04N19/635
• CPC Class Codes: H04N 19/132 Sampling, masking or truncation of coding units, e.g. adaptive resampling, frame skipping, frame interpolation or high-frequency transform coefficient masking
• CPC Class Codes: H04N 19/154 Measured or subjectively estimated visual quality after decoding, e.g. measurement of distortion use of rate-distortion criteria H04N19/147
• CPC Class Codes: H04N 19/172 the region being a picture, frame or field
• CPC Class Codes: H04N 19/176 the region being a block, e.g. a macroblock
• CPC Class Codes: H04N 19/436 using parallelised computational arrangements
• CPC Class Codes: H04N 19/44 Decoders specially adapted therefor, e.g. video decoders which are asymmetric with respect to the encoder
• CPC Class Codes: H04N 19/587 involving temporal sub-sampling or interpolation, e.g. decimation or subsequent interpolation of pictures in a video sequence
• CPC Class Codes: H04N 19/61 in combination with predictive coding
• CPC Class Codes: H04N 19/86 involving reduction of coding artifacts, e.g. of blockiness
• CPC Class Codes: H04N 19/89 involving methods or arrangements for detection of transmission errors at the decoder
• CPC Class Codes: H04N 19/91 Entropy coding, e.g. variable length coding [VLC] or arithmetic coding

Abstract

Video decoding innovations for multithreading implementations and graphics processor unit (“GPU”) implementations are described. For example, for multithreaded decoding, a decoder uses innovations in the areas of layered data structures, picture extent discovery, a picture command queue, and/or task scheduling for multithreading. Or, for a GPU implementation, a decoder uses innovations in the areas of inverse transforms, inverse quantization, fractional interpolation, intra prediction using waves, loop filtering using waves, memory usage and/or performance-adaptive loop filtering. Innovations are also described in the areas of error handling and recovery, determination of neighbor availability for operations such as context modeling and intra prediction, CABAC decoding, computation of collocated information for direct mode macroblocks in B slices, reduction of memory consumption, implementation of trick play modes, and picture dropping for quality adjustment.

Claims

1. A method comprising:

identifying a direct mode macroblock;

in response to the identifying, computing collocated macroblock information to be used in decoding of the direct mode macroblock; and

using the collocated macroblock information in reconstruction of the direct mode macroblock.

2. The method of claim 1 wherein the direct mode macroblock is in a B slice of a coded video bit stream.

3. The method of claim 1 wherein the computing the collocated macroblock information includes operations of retrieving zero, one or more motion vectors and retrieving zero, one or more reference picture indices.

4. The method of claim 1 wherein the collocated macroblock information is for a collocated macroblock in a picture of a reference picture list, and wherein the computing collocated macroblock information includes selecting among plural available routines to call depending on two or more of:

(a) spatial/temporal mode decision used for the direct mode macroblock, (b) picture format of a current picture, and (c) picture format of the picture in the reference picture list.

5. The method of claim 4 wherein the selecting is further based upon one or more of:

(d) macroblock pair format for a macroblock pair including the direct mode macroblock, and (e) macroblock position of the direct mode macroblock in the macroblock pair.

6. The method of claim 1 wherein the collocated macroblock information is macroblock-level collocated macroblock information, the method further comprising, before the identifying, computing slice-level collocated macroblock information to be used for one or more direct mode macroblocks in a B slice.

7. The method of claim 6 further comprising performing the identifying and the computing macroblock-level collocated macroblock information on a macroblock-by-macroblock basis for each of the one or more direct mode macroblocks in the B-slice.

8. The method of claim 6 wherein the slice-level collocated macroblock information includes scaling factors and field picture selections.

9. The method of claim 6 further comprising buffering the slice-level collocated macroblock and the macroblock-level collocated macroblock information for use in decoding direct mode macroblocks of the B slice.

10. The method of claim 1 wherein a multithreaded decoder performs the method in a motion vector setup stage.

11. A computer-readable medium storing computer-executable instructions for causing a computer system programmed thereby to perform the method of claim 1.

12. A method comprising

generating a task dependency graph that indicates dependencies between plural decoding tasks, wherein the plural decoding tasks include a collocated macroblock information task to be scheduled apart from entropy decoding tasks;

and

decoding video with multiple threads of execution using the task dependency graph.

13. The method of claim 12 wherein the collocated macroblock information task is an initial part of a motion compensation task.

14. The method of claim 12 wherein the collocated macroblock information task is also scheduled apart from a motion compensation task dependent on the collocated macroblock information task.

15. The method of claim 12 wherein, for the collocated macroblock information task, the decoding comprises selecting among plural available routines to call depending on two or more of:

(a) spatial/temporal mode decision used for the direct mode macroblock, (b) picture format of a current picture, and (c) picture format of the a picture in a reference picture list.

16. The method of claim 15 wherein the selecting is further based upon one or more of:

(d) macroblock pair format for a macroblock pair including the direct mode macroblock, and (e) macroblock position of the direct mode macroblock in the macroblock pair

17. A method comprising:

identifying a B slice of a first picture, the B slice having one or more direct mode macroblocks; and

for each of one or more collocated slices, remapping plural reference picture indices from a reference picture list of the collocated slice to a reference picture list of the B slice.

18. The method of claim 17 wherein the remapping includes, for each of the plural reference picture indices from the collocated slice:

finding a reference picture identifier for the reference picture index from the collocated slice;

determining whether the reference picture identifier matches any reference picture identifier for the reference picture list of the B slice;

if so, replacing the reference picture index from the collocated slice with a corresponding reference picture index from the B slice; and

otherwise, marking the reference picture index from the collocated slice as invalid for motion compensation of the one or more direct mode macroblocks in the B slice.

19. The method of claim 17 wherein a multithreaded decoder performs the method in a motion vector setup stage.

20. A computer-readable medium storing computer-executable instructions for causing a computer system programmed thereby to perform the method of claim 17.