CONTROL OF VIDEO COMPRESSION BASED ON FILE SIZE CONSTRAINT

• US 20080084925A1
• Filed: 10/10/2007
• Published: 04/10/2008
• Est. Priority Date: 10/10/2006
• Status: Active Grant

• Current Assignee: Flash Networks, Ltd. (Constellation Software Incorporated)
• Original Assignee: Mobixell Networks Incorporated (Constellation Software Incorporated)
• Inventors: Wexlur, Yosef, Rozen, Shaul, Raudnitz, Dan
• Granted Patent: US 9,247,259 B2
• Time in Patent Office: Days
• US Class Current: 375/240.01
• CPC Class Codes: H04N 19/124 Quantisation
• 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 19/152 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 19/176 the region being a block, e.g. a macroblock
• CPC Class Codes: H04N 19/40 using video transcoding, i.e. partial or full decoding of a coded input stream followed by re-encoding of the decoded output stream
• CPC Class Codes: H04N 19/61 in combination with predictive coding
• CPC Class Codes: H04N 19/85 using pre-processing or post-processing specially adapted for video compression

Abstract

A method for processing data includes receiving an image sequence including a succession of image frames for encoding in an image sequence file. A target size of the image sequence file is specified. The image sequence file is generated by encoding the succession of the image frames using at least one variable compression parameter, which is adjusted during the encoding responsively to the target size. The image sequence file is outputted for transmission over a communication link.

Claims

1. A method for processing data, comprising:

receiving an image sequence comprising a succession of image frames for encoding in an image sequence file;

specifying a target size of the image sequence file;

generating the image sequence file by encoding the succession of the image frames using at least one variable compression parameter, which is adjusted during the encoding responsively to the target size; and

outputting the image sequence file for transmission over a communication link.

2. The method according to claim 1, wherein the at least one variable compression parameter comprises a quantization parameter.

3. The method according to claim 2, wherein encoding the succession of the image frames comprises determining a buffer level of a virtual buffer responsively to a cumulative data volume of the image frames preceding a given frame in the succession, and setting the quantization parameter responsively to the buffer level.

4. The method according to claim 2, wherein encoding the succession of the image frames comprises dividing each of the image frames into a plurality of basic units, and setting the quantization parameter respectively for each of the basic units in each of the image frames.

5. The method according to claim 1, wherein the at least one variable compression parameter comprises a skip frame parameter, which is set so as to cause at least one of the image frames to be dropped from the image sequence file.

6. The method according to claim 1, wherein encoding the succession of the image frames comprises:

defining a virtual buffer size responsively to the target size;

defining a buffer overflow curve indicating an amount by which a data volume at each frame in the image sequence file is permitted to exceed a working point indicated by the virtual buffer size; and

controlling the variable compression parameter while encoding the data so that the data volume remains within a bound indicated by the buffer overflow curve.

7. The method according to claim 6, wherein the bound indicated by the buffer overflow curve decreases monotonically over at least a final portion of the succession of the image frames.

8. The method according to claim 6, wherein controlling the variable compression parameter comprises dropping a given frame from the image sequence file upon determining that inclusion of the given frame in the image sequence file will cause the data volume to exceed the bound indicated by the buffer overflow curve for the given frame.

9. The method according to claim 1, wherein encoding the succession of the image frames comprises compressing the image sequence in a single pass through the succession of the image frames.

10. The method according to claim 9, wherein the image sequence file generated in the single pass has a file size that is no greater than the target size and no less than 90% of the target size.

11. The method according to claim 10, wherein the file size is no less than 98% of the target size.

12. Apparatus for processing data, comprising:

a memory, which is configured to receive an image sequence comprising a succession of image frames for encoding in an image sequence file; and

a processor, which is coupled to generate the image sequence file by encoding the succession of the image frames using at least one variable compression parameter, while adjusting the at least one variable compression parameter during the encoding responsively to a specified target size of the image sequence file, and to output the image sequence file for transmission over a communication link.

13. The apparatus according to claim 12, wherein the at least one variable compression parameter comprises a quantization parameter.

14. The apparatus according to claim 13, wherein the processor is configured to determine a buffer level of a virtual buffer responsively to a cumulative data volume of the image frames preceding a given frame in the succession, and to set the quantization parameter responsively to the buffer level.

15. The apparatus according to claim 13, wherein the processor is configured to divide each of the image frames into a plurality of basic units, and to set the quantization parameter respectively for each of the basic units in each of the image frames.

16. The apparatus according to claim 12, wherein the at least one variable compression parameter comprises a skip frame parameter, which is set by the processor so as to cause at least one of the image frames to be dropped from the image sequence file.

17. The apparatus according to claim 12, wherein the processor is configured to encode the succession of the image frames by defining a virtual buffer size responsively to the target size, defining a buffer overflow curve indicating an amount by which a data volume at each frame in the image sequence file is permitted to exceed a working point indicated by the virtual buffer size, and controlling the variable compression parameter while encoding the data so that the data volume remains within a bound indicated by the buffer overflow curve.

18. The apparatus according to claim 17, wherein the bound indicated by the buffer overflow curve decreases monotonically over at least a final portion of the succession of the image frames.

19. The apparatus according to claim 17, wherein the processor is configured to drop a given frame from the image sequence file upon determining that inclusion of the given frame in the image sequence file will cause the data volume to exceed the bound indicated by the buffer overflow curve for the given frame.

20. The apparatus according to claim 12, wherein the processor is configured to encode the succession of the image frames in a single pass through the succession of the image frames.

21. The apparatus according to claim 20, wherein the image sequence file generated in the single pass has a file size that is no greater than the target size and no less than 90% of the target size.

22. The apparatus according to claim 21, wherein the file size is no less than 98% of the target size.

23. A computer software product, comprising a computer-readable medium in which program instructions are stored, which instructions, when read by a computer, cause the computer to receive an image sequence comprising a succession of image frames for encoding in an image sequence file, and to generate the image sequence file by encoding the succession of the image frames using at least one variable compression parameter, while adjusting the at least one variable compression parameter during the encoding responsively to a specified target size of the image sequence file, and to output the image sequence file for transmission over a communication link.

24. The product according to claim 23, wherein the at least one variable compression parameter comprises a quantization parameter.

25. The product according to claim 23, wherein the at least one variable compression parameter comprises a skip frame parameter, which is set by the computer so as to cause at least one of the image frames to be dropped from the image sequence file.