Video encoding method and apparatus with syntax element signaling of employed projection layout and associated video decoding method and apparatus

1. A video encoding method comprising:

setting a 360-degree Virtual Reality (360 VR) projection layout of projection faces, wherein the projection faces comprise a plurality of triangular projection faces located at a plurality of positions in the 360 VR projection layout, respectively;

encoding a frame having a 360-degree image content represented by the projection faces arranged in the 360 VR projection layout to generate a bitstream; and

for each position included in at least a portion of the positions, signaling at least one syntax element via the bitstream, wherein the at least one syntax element is set to indicate at least one of an index of a triangular projection view filled into a corresponding triangular projection face located at said each position and a rotation angle of content rotation applied to the triangular projection view filled into the corresponding triangular projection face located at said each position.

2. The video encoding method of claim 1 , wherein a number of the positions is N; the positions comprise (N−1) positions and a remaining position; for each of the (N−1) positions, a syntax element indicating an index of a triangular projection view filled into a corresponding triangular projection face located at said each of the (N−1) positions is signaled via the bitstream; and for the remaining position, no syntax element indicating an index of a remaining triangular projection view filled into a corresponding triangular projection face located at the remaining position is signaled via the bitstream.

3. The video encoding method of claim 1 , wherein a number of the positions is N; and for each of M positions in the positions, a syntax element indicating an index of a triangular projection view filled into a corresponding triangular projection face located at said each of the M positions is signaled via the bitstream, where signaled syntax elements indicative of indexes for the M positions have a same bit length, and M=N or (N−1).

4. The video encoding method of claim 1 , wherein for said each position included in said at least a portion of the positions, the triangular projection view filled into the corresponding triangular projection face located at said each position is selected from a view array of triangular projection views, and the index of the triangular projection view is set by an array index of the triangular projection view in the view array, wherein after the triangular projection view is selected for said each position, the view array is updated by removing the triangular projection view from the view array; syntax elements respectively indicating indexes of triangular projection views filled into corresponding triangular projection faces located at all positions in said at least a portion of the positions are signaled via the bitstream, and not all of the syntax elements have a same bit length.

5. The video encoding method of claim 1 , wherein, for each of the positions, a syntax element indicating a rotation angle of content rotation applied to a triangular projection view filled into a corresponding triangular projection face located at said each of the positions is signaled via the bitstream.

6. The video encoding method of claim 5 , wherein the rotation angle is selected from a group consisting of 0°, 120° and 240°.

7. A video encoding method comprising:

encoding a frame having a 360-degree image content represented by projection faces arranged in a 360-degree Virtual Reality (360 VR) projection layout to generate a bitstream, wherein the projection faces comprise a plurality of triangular projection faces; and

signaling a first syntax element via the bitstream, wherein when a predefined projection layout is selected and used as the 360 VR projection layout, the first syntax element is set to indicate selection of the predefined projection layout.

8. The video encoding method of claim 7 , further comprising:

selecting the predefined projection layout from a set of different predefined projection layouts; and

setting the 360 VR projection layout by the predefined projection layout.

9. The video encoding method of claim 7 , wherein the first syntax element is set to indicate that the predefined projection layout is not selected and used as the 360 VR projection layout, and the video encoding method further comprises:

setting the 360 VR projection layout, wherein the triangular projection faces are located at a plurality of positions in the 360 VR projection layout, respectively; and

for each position included in at least a portion of the positions, signaling at least one second syntax element via the bitstream, wherein the at least one second syntax element is set to indicate at least one of an index of a triangular projection view filled into a corresponding triangular projection face located at said each position and a rotation angle of content rotation applied to the triangular projection view filled into the corresponding triangular projection face located at said each position.

10. A video decoding method comprising:

receiving a bitstream;

processing the bitstream to obtain at least one syntax element for each position included in at least a portion of a plurality of positions;

referring to at least syntax elements obtained for said at least a portion of the positions to determine a 360-degree Virtual Reality (360 VR) projection layout of projection faces, wherein the projection faces comprise a plurality of triangular projection faces located at the positions in the 360 VR projection layout, respectively, and the at least one syntax element indicates at least one of an index of a triangular projection view filled into a corresponding triangular projection face located at said each position and a rotation angle of content rotation applied to the triangular projection view filled into the corresponding triangular projection face located at said each position; and

decoding the bitstream to generate a decoded frame having a 360-degree image content represented by the projection faces arranged in the 360 VR projection layout.

11. The video decoding method of claim 10 , wherein a number of the positions is N; the positions comprise (N−1) positions and a remaining position; for each of the (N−1) positions, a syntax element indicating an index of a triangular projection view filled into a corresponding triangular projection face located at said each of the (N−1) positions is derived from the bitstream; and for the remaining position, no syntax element indicating an index of a remaining triangular projection view filled into a corresponding triangular projection face located at the remaining position is derived from the bitstream.

12. The video decoding method of claim 10 , wherein a number of the positions is N; and for each of M positions in the positions, a syntax element indicating an index of a triangular projection view filled into a corresponding triangular projection face located at said each of the M positions is derived from the bitstream, where derived syntax elements indicative of indexes for the M positions have a same bit length, and M=N or (N−1).

13. The video decoding method of claim 10 , wherein for said each position included in said at least a portion of the positions, the triangular projection view filled into the corresponding triangular projection face located at said each position is determined from a view array of triangular projection views, and an array index of the triangular projection view in the view array is determined by the index of the triangular projection view, wherein after the triangular projection view is determined for said each position, the view array is updated by removing the triangular projection view from the view array; syntax elements indicating indexes of triangular projection views filled into corresponding triangular projection faces located at all positions included in said at least a portion of the positions are derived from the bitstream, and not all of the derived syntax elements have a same bit length.

14. The video decoding method of claim 10 , wherein, for each of the positions, a syntax element indicating a rotation angle of content rotation applied to a triangular projection view filled into a corresponding triangular projection face located at said each of the positions is derived from the bitstream.

15. The video decoding method of claim 14 , wherein the rotation angle is selected from a group consisting of 0°, 120° and 240°.

16. A video decoding method comprising:

receiving a bitstream;

processing the bitstream to obtain a first syntax element;

referring to at least the first syntax element to determine a 360-degree Virtual Reality (360 VR) projection layout of projection faces, wherein the projection faces comprise a plurality of triangular projection faces, and when a predefined projection layout is selected and used as the 360 VR projection layout, the first syntax element indicates selection of the predefined projection layout; and

decoding the bitstream to generate a decoded frame having a 360-degree image content represented by the projection faces arranged in the 360 VR projection layout.

17. The video decoding method of claim 16 , wherein referring to at least the first syntax element to determine the 360 VR projection layout of the projection faces comprises:

selecting the predefined projection layout from a set of different predefined projection layouts according to the first syntax element; and

determining that the 360 VR projection layout is the predefined projection layout.

18. The video decoding method of claim 16 , wherein the first syntax element does not indicate selection of the predefined projection layout, and the video decoding method further comprises:

processing the bitstream to obtain at least one second syntax element for each position included in at least a portion of a plurality of positions, wherein the triangular projection faces are located at the positions, respectively, and the at least one second syntax element indicates at least one of an index of a triangular projection view filled into a corresponding triangular projection face located at said each position and a rotation angle of content rotation applied to the triangular projection view filled into the corresponding triangular projection face located at said each position;

referring to at least the first syntax element to determine the 360 VR projection layout of the projection faces further comprises:

referring to syntax elements obtained for said at least a portion of the positions to determine the 360 VR projection layout.

19. A video encoder comprising:

a control circuit, arranged to set a 360-degree Virtual Reality (360 VR) projection layout of projection faces, wherein the projection faces comprise a plurality of triangular projection faces located at a plurality of positions in the 360 VR projection layout, respectively; and

an encoding circuit, arranged to encode a frame having a 360-degree image content represented by the projection faces arranged in the 360 VR projection layout to generate a bitstream, wherein for each position included in at least a portion of the positions, the encoding circuit further signals at least one syntax element via the bitstream, where the at least one syntax element is set to indicate at least one of an index of a triangular projection view filled into a corresponding triangular projection face located at said each position and a rotation angle of content rotation applied to the triangular projection view filled into the corresponding triangular projection face located at said each position.

20. A video decoder comprising:

a decoding circuit, arranged to receive a bitstream, process the bitstream to obtain at least one syntax element for each position included in at least a portion of a plurality of positions, and decode the bitstream to generate a decoded frame having a 360-degree image content represented by projection faces arranged in a 360-degree Virtual Reality (360 VR) projection layout; and

a control circuit, arranged to refer to at least syntax elements obtained for said at least a portion of the positions to determine the 360 VR projection layout of the projection faces, wherein the projection faces comprise a plurality of triangular projection faces located at the positions in the 360 VR projection layout, respectively, and the at least one syntax element indicates at least one of an index of a triangular projection view filled into a corresponding triangular projection face located at said each position and a rotation angle of content rotation applied to the triangular projection view filled into the corresponding triangular projection face located at said each position.