Method and apparatus for selecting a reference frame for motion estimation in video encoding
View Patent ↗Method and apparatus for selecting a reference frame for motion estimation in a video encoder is described. In one example, motion estimation is performed on a current macroblock in a current frame with respect to a reference frame to obtain a motion vector, a sum of absolute difference (SAD), a global motion vector, and an average SAD. A first relative change of the motion vector with respect to the global motion vector is computed. A second relative change of the SAD with respect to the average SAD is computed. A functional based on the first relative change, the second relative change, a first parameter, and a second parameter is computed. The functional is compared with a threshold. The reference frame is selected if the functional satisfies the threshold.
1. A method of selecting a reference frame for encoding a video, comprising:
performing motion estimation on a current macroblock in a current frame with respect to a reference frame to obtain a motion vector, a sum of absolute difference (SAD), a global motion vector, and an average SAD;
computing a first relative change of the motion vector with respect to the global motion vector;
computing a second relative change of the SAD with respect to the average SAD;
computing a functional based on the first relative change, the second relative change, a first parameter, and a second parameter;
comparing the functional to at least one threshold; and
selecting the reference frame if the functional satisfies the at least one threshold.
2. The method of claim 1 , further comprising:
repeating the steps of performing, computing the first relative change, computing the second relative change, computing the functional, comparing, and selecting with another reference frame if the functional does not satisfy the at least one threshold.
3. The method of claim 1 , wherein the functional comprises an x-component and a y-component, wherein the x-component of the functional comprises the sum of (1) an x-component of the first parameter times the an x-component of the first relative change and (2) an x-component of the second parameter times the second relative change, and wherein the y-component of the functional comprises the sum of (1) a y-component of the first parameter times a y-component of the first relative change and (2) a y-component of the second parameter times the second relative change.
4. The method of claim 3 , wherein the at least one threshold comprises a first threshold, and wherein the step of comparing comprises:
comparing the x-component of the functional with the first threshold; and
comparing the y-component of the functional with the first threshold.
5. The method of claim 4 , wherein the reference frame is selected if both the x-component of the functional and the y-component of the functional satisfy the first threshold.
6. The method of claim 3 , wherein the at least one threshold comprises a first threshold and a second threshold, and wherein the step of comparing comprises:
comparing the x-component of the first relative change with the first threshold;
comparing the y-component of the first relative change with the first threshold; and
comparing the second relative change with the second threshold.
7. The method of claim 6 , wherein the reference frame is selected if (1) one or both the x-component of the first relative change and the y-component of the first relative change satisfy the first threshold and (2) the second relative change satisfies the second threshold.
8. A computer readable medium having instructions stored thereon that when executed by a processor cause the processor to perform a method of selecting a reference frame for encoding a video, comprising:
performing motion estimation on a current macroblock in a current frame with respect to a reference frame to obtain a motion vector, a sum of absolute difference (SAD), a global motion vector, and an average SAD;
computing a first relative change of the motion vector with respect to the global motion vector;
computing a second relative change of the SAD with respect to the average SAD;
computing a functional based on the first relative change, the second relative change, a first parameter, and a second parameter;
comparing the functional to at least one threshold; and
selecting the reference frame if the functional satisfies the at least one threshold.
9. The computer readable medium of claim 8 , further comprising:
repeating the steps of performing, computing the first relative change, computing the second relative change, computing the functional, comparing, and selecting with another reference frame if the functional does not satisfy the at least one threshold.
10. The computer readable medium of claim 8 , wherein the functional comprises an x-component and a y-component, wherein the x-component of the functional comprises the sum of (1) an x-component of the first parameter times the an x-component of the first relative change and (2) an x-component of the second parameter times the second relative change, and wherein the y-component of the functional comprises the sum of (1) a y-component of the first parameter times a y-component of the first relative change and (2) a y-component of the second parameter times the second relative change.
11. The computer readable medium of claim 10 , wherein the at least one threshold comprises a first threshold, and wherein the step of comparing comprises:
comparing the x-component of the functional with the first threshold; and
comparing the y-component of the functional with the first threshold.
12. The computer readable medium of claim 11 , wherein the reference frame is selected if both the x-component of the functional and the y-component of the functional satisfy the first threshold.
13. The computer readable medium of claim 10 , wherein the at least one threshold comprises a first threshold and a second threshold, and wherein the step of comparing comprises:
comparing the x-component of the first relative change with the first threshold;
comparing the y-component of the first relative change with the first threshold; and
comparing the second relative change with the second threshold.
14. The computer readable medium of claim 13 , wherein the reference frame is selected if (1) one or both the x-component of the first relative change and the y-component of the first relative change satisfy the first threshold and (2) the second relative change satisfies the second threshold.
15. Apparatus for selecting a reference frame for encoding a video, comprising:
means for performing motion estimation on a current macroblock in a current frame with respect to a reference frame to obtain a motion vector, a sum of absolute difference (SAD), a global motion vector, and an average SAD;
means for computing a first relative change of the motion vector with respect to the global motion vector;
means for computing a second relative change of the SAD with respect to the average SAD;
means for computing a functional based on the first relative change, the second relative change, a first parameter, and a second parameter;
means for comparing the functional to at least one threshold; and
means for selecting the reference frame if the functional satisfies the at least one threshold.
16. The apparatus of claim 15 , wherein the functional comprises an x-component and a y-component, wherein the x-component of the functional comprises the sum of (1) an x-component of the first parameter times the an x-component of the first relative change and (2) an x-component of the second parameter times the second relative change, and wherein the y-component of the functional comprises the sum of (1) a y-component of the first parameter times a y-component of the first relative change and (2) a y-component of the second parameter times the second relative change.
17. The apparatus of claim 16 , wherein the at least one threshold comprises a first threshold, and wherein the means for comparing comprises:
means for comparing the x-component of the functional with the first threshold; and
means for comparing the y-component of the functional with the first threshold.
18. The apparatus of claim 17 , wherein the reference frame is selected if both the x-component of the functional and the y-component of the functional satisfy the first threshold.
19. The apparatus of claim 16 , wherein the at least one threshold comprises a first threshold and a second threshold, and wherein the means for comparing comprises:
means for comparing the x-component of the first relative change with the first threshold;
means for comparing the y-component of the first relative change with the first threshold; and
means for comparing the second relative change with the second threshold.
20. The apparatus of claim 19 , wherein the reference frame is selected if (1) one or both the x-component of the first relative change and the y-component of the first relative change satisfy the first threshold and (2) the second relative change satisfies the second threshold.