Digital video signal encoder and encoding method

• US 6,317,459 B1
• Filed: 08/25/2000
• Issued: 11/13/2001
• Est. Priority Date: 03/14/1997
• Status: Expired due to Term

• Current Assignee: Microsoft Technology Licensing LLC (Microsoft Corporation)
• Original Assignee: Microsoft Corporation
• Inventors: Wang, Albert S.
• Primary Examiner(s): BRITTON, HOWARD W
• Application Number:
  US09/648,509
• Time in Patent Office: 445 Days
• Field of Search: H04/N.750, 375/240.12, 375/240.04, 375/240.03, 348/407.1, 348/405.1, 348/409.1, 348/411.1, 348/412.1, 348/415.1, 348/420.1, 348/384.1, 348/399.1
• US Class Current: 375/240.12
• 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 19/126 Details of normalisation or weighting functions, e.g. normalisation matrices or variable uniform quantisers
• CPC Class Codes: H04N 19/137 Motion inside a coding unit, e.g. average field, frame or block difference
• CPC Class Codes: H04N 19/142 Detection of scene cut or scene change
• CPC Class Codes: H04N 19/147 according to rate distortion criteria rate-distortion as a criterion for motion estimation H04N19/567
• 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 19/179 the unit being a scene or a shot
• CPC Class Codes: H04N 19/19 using optimisation based on Lagrange multipliers

Abstract

A motion video signal encoder maximizes image quality without exceeding transmission bandwidth available to carry the encoded motion video signal by comparing encoded frames of the motion video signal to a desired size of frame. If the size of encoded frames differ from the desired size, encoding is adjusted to produce encoded frames closer in size to the desired size. In addition, a cumulative bandwidth error records an accumulated amount of available bandwidth. The cumulative bandwidth error is adjusted as time elapses to add to the available bandwidth and as each frame is encoded to thereby consume bandwidth. As the cumulative bandwidth error grows in magnitude above or below zero, encoding is adjusted as needed to either improve image quality to more completely consume available bandwidth or to reduce image quality to thereby consume less bandwidth and to thereby cause the cumulative bandwidth error to move toward zero. Rapid changes in the amount of change or motion in the motion video signal are detected by comparing the amount of change between two consecutive frames and filtering the amount of change with previously measured amounts of change. Encoding is pre-compensated according to the filtered measurement of rapid change.

Claims

1. A method for encoding a motion video signal, the method comprising:

measuring a first difference between first and second frames of the motion video signal;

measuring a second difference between the second frame and a third frame of the motion video signal;

filtering the first and second differences to form a filtered difference;

adjusting an encoding parameter in accordance with the second difference and the filtered difference; and

encoding the third frame according to the encoding parameter as adjusted.

2. The method of claim 1 wherein the first and second differences are absolute pixel differences.

3. A computer readable medium useful in association with a computer which includes a processor and a memory, the computer readable medium including computer instructions which are configured to cause the computer to encode a motion video signal by performing the steps of:

measuring a first difference between first and second frames of the motion video signal;

measuring a second difference between the second frame and a third frame of the motion video signal;

filtering the first and second differences to form a filtered difference;

adjusting an encoding parameter in accordance with the second difference and the filtered difference; and

encoding the third frame according to the encoding parameter as adjusted.

4. The computer readable medium of claim 3 wherein the first and second differences are absolute pixel differences.

5. A computer system comprising:

a processor;

a memory operatively coupled to the processor; and

a motion video signal encoder which executes in the processor from the memory and which, when executed by the processor, causes the computer to encode a motion video signal by performing the steps of;

measuring a first difference between first and second frames of the motion video signal;

measuring a second difference between the second frame and a third frame of the motion video signal;

filtering the first and second differences to form a filtered difference;

adjusting an encoding parameter in accordance with the second difference and the filtered difference; and

encoding the third frame according to the encoding parameter as adjusted.

6. The computer system of claim 5 wherein the first and second differences are absolute pixel differences.

7. A method for encoding a motion video signal, the method comprising:

measuring a first difference between first and second frames of the motion video signal;

measuring a second difference between the second frame and a third frame of the motion video signal;

determining a third difference between the first and second differences;

comparing the third difference to a predetermined threshold;

adjusting a quantization parameter if the third difference is greater than the predetermined threshold; and

encoding the third frame according to the quantization parameter as adjusted.

8. The method of claim 7 wherein the first and second differences are absolute pixel differences.

9. The method of claim 7 wherein comparing the third difference comprises determining that the second difference is greater than the first difference;

and

further wherein adjusting the quantization parameter comprises increasing the quantization parameter.

10. The method of claim 7 wherein comparing the third difference comprises determining that the second difference is less than the first difference;

and

further wherein adjusting the quantization parameter comprises decreasing the quantization parameter.

11. A computer readable medium useful in association with a computer which includes a processor and a memory, the computer readable medium including computer instructions which are configured to cause the computer to perform a method comprising:

measuring a first difference between first and second frames of the motion video signal;

measuring a second difference between the second frame and a third frame of the motion video signal;

determining a third difference between the first and second differences;

comparing the third difference to a predetermined threshold;

adjusting a quantization parameter if the third difference is greater than the predetermined threshold; and

encoding the third frame according to the quantization parameter as adjusted.

12. The computer readable medium of claim 11 wherein the first and second differences are absolute pixel differences.

13. The computer readable medium of claim 11 wherein comparing comprises determining that the second difference is greater than the first difference;

and

further wherein adjusting comprises increasing the quantization parameter.

14. The computer readable medium of claim 11 wherein comparing comprises determining that the second difference is less than the first difference;

and

further wherein adjusting comprises decreasing the quantization parameter.

15. A computer system comprising:

a processor,

a memory operatively coupled to the processor; and

a motion video signal encoder which executes in the processor from the memory and which, when executed by the processor, performs the tasks of;

measuring a first difference between first and second frames of the motion video signal;

measuring a second difference between the second frame and a third frame of the motion video signal;

determining a third difference between the first and second differences;

comparing the third difference to a predetermined threshold;

adjusting a quantization parameter if the third difference is greater than the predetermined threshold; and

encoding the third frame according to the quantization parameter as adjusted.

16. The computer system of claim 15 wherein the first and second differences are absolute pixel differences.

17. The computer system of claim 15 wherein the task of comparing comprises determining that the second difference is greater than the first difference;

and

further wherein the task of adjusting comprises increasing the quantization parameter.

18. The computer system of claim 15 wherein the task of comparing comprises determining that the second difference is less than the first difference;

and

further wherein the task of adjusting comprises decreasing the quantization parameter.