Reducing motion vector information transmission in bi-directional temporal prediction
A method for inter-coding video is provided in which transmission bandwidth requirements associated with second motion vectors for bi-directional temporal prediction is reduced. In the method motion vector information for only one of the two motion vectors for bi-directional temporal prediction can be transmitted together with information on how to derive or construct the second motion vector. Thus, rather than sending express information regarding two motion vectors, express information related to only one motion vector along with information related to reconstruction/derivation of the second motion vector is transmitted, thus reducing bandwidth requirements and increasing coding efficiency.
1. A method of decoding a video included in a bitstream comprising:
(a) receiving a rectangular coding unit of luma samples included in a bi-predictive B-slice of a current frame of said video;
(b) receiving a first motion vector associated with said coding unit of said bi-predictive B-slice of said current frame of said video referencing a temporally previous reference slice of a temporally previous reference frame relative to said current frame of said coding unit;
(c) receiving a second motion vector associated with said coding unit of said bi-predictive B-slice of said current frame of said video referencing a temporally future reference slice of a temporally future reference frame relative to said current frame of said coding unit;
(d) applying an optical flow between said temporally previous reference slice and said temporally future reference slice to perform a sample based motion modification after motion compensation based upon at least one of said first motion vector and said second motion vector; and
(e) decoding said coding unit based upon said sample based motion modification as a result of said applying said optical flow between said temporally previous reference slice and said temporally future reference slice.
2. The method of decoding of claim 1 wherein said modifying comprises information sufficient to reconstruct an MVP index and an MVD of said second motion vector.
3. The method of decoding of claim 1 wherein said modifying comprises a scaling factor.
4. The method of decoding of claim 1 wherein said modifying comprises said second motion vector is a mirror image of said first motion vector.
5. The method of decoding of claim 1 wherein said coding unit is greater than a predefined size.
6. The method of decoding of claim 1 wherein said second motion vector is partially derived based upon said first motion vector.
7. The method of decoding of claim 1 wherein said second motion vector is fully derived based upon said first motion vector.
8. The method of decoding of claim 1 wherein said second motion vector is a scaled version of said first motion vector.
9. The method of decoding of claim 1 wherein said first motion vector is stored in a reference list.
10. The method of decoding of claim 9 wherein said second motion vector is stored in a reference list.