Low complexity affine merge mode for versatile video coding

1. A method for reduced memory utilization for motion data derivation in encoded video, comprising:

determining, by a video decoder of a device from an input video bitstream, one or more control point motion vectors of a first prediction unit of a first coding tree unit, based on a plurality of motion vectors of one or more second prediction units neighboring the first prediction unit stored in a motion data line buffer of the device, the one or more second prediction units from a second coding tree unit neighboring the first coding tree unit; and

decoding, by the video decoder, one or more sub-blocks of the first prediction unit based on the determined one or more control point motion vectors.

2. The method of claim 1 , wherein the one or more second prediction units are located at a top boundary of the first coding tree unit.

3. The method of claim 2 , wherein the plurality of motion vectors of the one or more second prediction units are stored in the motion data line buffer of the device during decoding of the first coding tree unit.

4. The method of claim 3 , further comprising deriving the one or more control point motion vectors of the first prediction unit proportional to an offset between a sample position of the first prediction unit and a sample position of the one or more second prediction units.

5. The method of claim 3 , further comprising:

determining, by the video decoder, one or more second control point motion vectors of another prediction unit of the first coding tree unit based on the one or more control point motion vectors, responsive to one or more third prediction units neighboring the another prediction unit not being located at the top boundary of the first coding tree unit; and

decoding, by the video decoder, one or more sub-blocks of the another prediction unit based on the determined one or more second control point motion vectors.

6. The method of claim 1 , wherein determining the one or more control point motion vectors further comprises calculating an offset from motion data of the one or more second prediction units neighboring the first prediction unit based on a height or width of the one or more second prediction units.

7. The method of claim 6 , wherein an identification of the height or width of the one or more second prediction units is stored in an affine motion data line buffer.

8. The method of claim 1 , wherein decoding the one or more sub-blocks of the first prediction unit based on the determined one or more control point motion vectors further comprises deriving sub-block motion data of the one or more sub-blocks based on the determined one or more control point motion vectors.

9. The method of claim 1 , further comprising providing, by the video decoder to a display device, the decoded one or more sub-blocks of the first prediction unit.

10. A system for reduced memory utilization for motion data derivation in encoded video, comprising:

a motion data line buffer; and

a video decoder, configured to:

determine, from an input video bitstream, one or more control point motion vectors of a first prediction unit of a first coding tree unit, based on a plurality of motion vectors of one or more second prediction units neighboring the first prediction unit stored in the motion data line buffer, the one or more second prediction units from a second coding tree unit neighboring the first coding tree unit, and

decode one or more sub-blocks of the first prediction unit based on the determined one or more control point motion vectors.

11. The system of claim 10 , wherein the one or more second prediction units are located at a top boundary of the first coding tree unit.

12. The system of claim 11 , wherein the plurality of motion vectors of the one or more second prediction units are stored in the motion data line buffer during decoding of the first coding tree unit.

13. The system of claim 12 , wherein the video decoder is further configured to derive the one or more control point motion vectors of the first prediction unit proportional to an offset between a sample position of the first prediction unit and a sample position of the one or more second prediction units.

14. The system of claim 12 , wherein the video decoder is further configured to:

determine one or more second control point motion vectors of another prediction unit of the first coding tree unit based on the one or more control point motion vectors, responsive to one or more third prediction units neighboring the another prediction unit not being located at the top boundary of the first coding tree unit, and

decode one or more sub-blocks of the another prediction unit based on the determined one or more second control point motion vectors.

15. The system of claim 10 , wherein the video decoder is further configured to calculate an offset from motion data of the one or more second prediction units neighboring the first prediction unit based on a height or width of the one or more second prediction units.

16. The system of claim 15 , further comprising an affine motion data line buffer configured to store an identification of the height or width of the one or more second prediction units.

17. The system of claim 10 , wherein the video decoder is further configured to derive sub-block motion data of the one or more sub-blocks based on the determined one or more control point motion vectors.

18. A method for reduced memory utilization for motion data derivation in encoded video, comprising:

for a first prediction unit of a first coding tree unit of an input video bitstream, determining, by a video decoder of a device, whether one or more second prediction units neighboring the first prediction unit are located at a top boundary of the first coding tree unit, the one or more second prediction units stored in a motion data line buffer of the device;

either:

(i) responsive to the one or more second prediction units being located at the top boundary of the first coding tree unit, deriving motion vectors for the first prediction unit from motion vectors of the one or more second prediction units, or

(ii) responsive to the one or more second prediction units not being located at the top boundary of the first coding tree unit, deriving motion vectors for the first prediction unit from one or more control point motion vectors of the one or more second prediction units; and

decoding, by the video decoder, one or more sub-blocks of the first prediction unit based on the derived motion vectors.