Adaptive motion estimation coding

1. A method for encoding a video signal comprising a plurality of reference frames, and non-reference frames, the method comprising:

analyzing motion vectors of at least a portion of a first reference frame only without analyzing motion vectors of non-reference frames, the first reference frame being a backward reference frame for a non-reference frame;

when motion vector statistics of the motion vectors are less than or equal to a preset threshold, determining a reference frame that is close to the non-reference frame; and

duplicating at least a portion of the determined reference frame as at least a portion of the non-reference frame.

2. The method of claim 1 , wherein the step of duplicating the determined reference frame as the non-reference frame further comprises:

duplicating the determined reference frame for a plurality of non-reference frames that utilize the first reference frame as a backward reference frame.

3. The method of claim 2 , wherein the determined reference frame comprises the first determined reference frame and a second determined reference frame, and the step of duplicating the determined reference frame for a plurality of non-reference frames further comprises:

duplicating the first determined reference frame as some of the plurality of non-reference frames; and

duplicating the second determined reference frame as remaining frames of the plurality of non-reference frames.

4. The method of claim 1 , further comprising:

setting all motion vectors of the non-reference frame to zero.

5. The method of claim 1 , wherein the step of duplicating a portion of the determined reference frame as a portion of the non-reference frame comprises:

setting a prediction direction of the portion of the non-reference frame toward the determined reference frame, and setting motion vectors and coded block patterns corresponding to the portion of the non-reference frame to zero.

6. A method for encoding a video signal comprising a plurality of reference frames and non-reference frames, the method comprising:

for a non-reference frame to be encoded, determining if at least a portion of a reference frame that is a backward reference frame of the non-reference frame has no scene change by analyzing the reference frame only, without analyzing motion vectors of the non-reference frame; and

when the portion of the reference frame has no scene change, scaling down a search range for block matching of the portion of the non-reference frame.

7. The method of claim 6 wherein the step of scaling down a search range comprises:

determining a target motion vector of the reference frame based on motion vector statistics;

calculating a target motion vector of the non-reference frame by multiplying a scaling factor with the target motion vector of the reference frame; and

scaling down the search range according to the target motion vector of the non-reference frame.

8. The method of claim 7 , wherein the reference frame is a backward reference frame of a plurality of non-reference frames and the step of calculating a target motion vector of the non-reference frame comprises:

deriving a scaling factor for each non-reference frame according to a number of non-reference frames and a displaying order relative to the reference frame.

9. The method of claim 6 , wherein the step of scaling down a search range for block matching of the non-reference frame comprises:

dividing the non-reference frame into partitions; and

independently scaling down the search range for each partition.

10. A method for encoding a video signal comprising a plurality of video frames, the method comprising:

down-scaling data of at least a portion of a first video frame only with a scaling factor;

determining motion information of the down-scaled video frame only; and

utilizing the motion information of the down-scaled video frame to scale down a search range for the video frame without reference to motion information of other video frames.

11. The method of claim 10 , further comprising:

performing a coarse search on the down-scaled video frame to determine the motion information of the down-scaled video frame.

12. The method of claim 11 , wherein the step of performing the coarse search comprises: further determining a maximum motion vector of the down-scaled video frame as the motion information; and

scaling down the search range according to the determined maximum motion vector and the scaling factor.

13. The method of claim 12 , wherein the first video frame is a backward reference frame of a plurality of non-reference frames and the method further comprises:

deriving a target motion vector for each non-reference frame in accordance with the maximum motion vector of the down-scaled video frame and a displaying order of each non-reference frame; and

scaling down a search range for each of the non-reference frames according to the target motion vector of each non-reference frame.

14. The method of claim 10 , wherein the step of utilizing the motion information of the down-scaled video frame to scale down a search range for the video frame comprises:

dividing the video frame into partitions; and

independently scaling down the search range for each partition according to the motion information of the corresponding partition.