Management and selection of reference frames for long term prediction in motion estimation

1. A method for selecting a reference frame in a frame buffer for encoding a current frame in a video encoding system, the method comprising:

storing in a frame buffer a plurality of reference frames, each reference frame associated with a characteristic metric vector, the characteristic metric vector representing the reference frame in a frequency domain;

generating for the current frame a characteristic metric vector representing the current frame in a frequency domain;

determining an interframe distance between the current frame and at least one of the reference frames, the interframe distance based upon a distance between the characteristic metric vector of the current frame the characteristic metric vector of the reference frame; and

selecting for encoding the current frame at least one reference frame for which the interframe distance is below a threshold distance.

2. The method of claim 1 , wherein the interframe distance Δ i,j is

Δ

i

,

j

=

∑

n

=

1

D

⁢

⁢

(

x

i

,

n

-

x

j

,

n

)

2

where i is the current frame, j is reference frame, and D is the number of components in the characteristic metric vector.

3. The method of claim 1 , wherein the threshold distance is a function of a number of dimensions of characteristic metric vector.

4. The method of claim 1 , wherein the threshold distance is a function of an encoding time constraint.

5. The method of claim 1 , wherein the interframe distance between the two frames is divided by a number of blocks in the current frame, prior to comparison with the threshold distance.

6. The method of claim 1 , wherein the interframe distance is standardized to be independent of a resolution of the frame.

7. The method of claim 1 , wherein selecting, for encoding the current frame, at least one reference frame for which the interframe distance is below the threshold distance comprises:

selecting the reference frame for which an average interblock distance between corresponding blocks of the current frame and reference frame is below the threshold distance.

8. A method for selecting reference frames for encoding a current frame in a video encoding system, wherein the current frame includes a plurality of blocks, the method comprising:

storing in a frame buffer a plurality of reference frames, each reference frame comprising a plurality of blocks, each block associated with a characteristic metric vector, the characteristic metric vector representing the block of the reference frame in a frequency domain;

generating for each block of the current frame a characteristic metric vector representing the block of the current frame in the frequency domain;

for each block of the current frame being a current block:

determining an interblock distance between the block of the current frame and each of those corresponding blocks in the plurality of reference frames, the interblock distance based upon a distance between the characteristic vector of the current block and each of those corresponding blocks in the plurality of reference frames; and

selecting for encoding the current block those corresponding blocks in the plurality of reference frames for which the interblock distance is below a threshold distance.

9. An apparatus for selecting a reference frame in a frame buffer for encoding a current frame in a video encoding system, the apparatus comprising:

a frame buffer for storing a plurality of reference frames, each reference frame associated with a characteristic metric vector, the characteristic metric vector representing the reference frame in a frequency domain;

means for generating for the current frame a characteristic metric vector representing the current frame in the frequency domain;

means for determining an interframe distance between the current frame and each reference frame, the interframe distance based upon a distance between the characteristic metric vector of the current frame the characteristic metric vector of the reference frame;

means for selecting for encoding the current frame at least one reference frame for which the interframe distance is below a threshold distance.

10. The apparatus of claim 9 , wherein the means for generating comprises:

a characteristic metric vector generation circuit adapted to receive a frame, generate from the frame a characteristic metric vector representing the frame in a frequency domain, and provide the frame and characteristic metric vector to the frame buffer for storage.

11. The apparatus of claim 9 , wherein the means for selecting comprises:

motion estimation circuit adapted to select for encoding the current frame at least one reference frame having a characteristic metric vector within a threshold distance to the characteristic metric vector of the current frame.

12. An apparatus for selecting reference frames for encoding a current frame in a video encoding system, wherein the current frame includes a plurality of blocks, the apparatus comprising:

a frame buffer for storing a plurality of reference frames, each reference frame comprising a plurality of blocks, each block associated with a characteristic metric vector, the characteristic metric vector representing the block of the reference frame in a frequency domain;

means for generating for each block of the current frame a characteristic metric vector representing the block of the current frame in the frequency domain; and

means for each block of the current frame:

determining an interblock distance between the block of the current frame and each of those corresponding blocks in the plurality of reference frames, the interblock distance based upon a distance between the characteristic vector of the current block and each of those corresponding blocks in the plurality of reference frames; and

selecting for encoding the current block of the current frame those corresponding blocks in the plurality of reference frames for which the interblock distance is below a threshold distance.

13. The method of claim 1 , wherein generating for the current frame a characteristic metric vector comprises transforming the current frame based on a Fourier Transform.

14. The method of claim 1 , wherein generating for the current frame a characteristic metric vector comprises transforming the current frame based on a Discrete Cosine Transform.

15. The method of claim 1 , wherein the characteristic metric vector of a reference frame or the current frame is generated by a frequency domain transform of at least one of a luminance, a chrominance, or a domain statistic of luminance or chrominance of the frame.

16. The apparatus of claim 9 , wherein characteristic metric vector for a frame comprises a vector generated by transforming the frame based on a Fourier Transform.

17. The apparatus of claim 9 , wherein characteristic metric vector for a frame comprises a vector generated by transforming the frame based on a Discrete Cosine Transform.

18. The apparatus of claim 9 , wherein the characteristic metric vector of a reference frame or the current frame is frequency domain transform of at least one of a luminance, a chrominance, or a domain statistic of luminance or chrominance of the frame.