Secondary transform set selection

A method of video encoding performed at a computing system having memory and one or more processors, the method comprising:

• receiving video data comprising a plurality of blocks including a current block;
• identifying an intra prediction mode for the current block;
• determining whether to change the intra prediction mode when deriving a transform set index;
• deriving the transform set index for the current block based on the intra prediction mode and the determination as to whether to change the intra prediction mode;
• selecting a first transform set from a plurality of transform sets according to the transform set index;
• and
• encoding the current block using the first transform set.

A non-transitory computer-readable storage medium storing a video bitstream that is generated by a video encoding method, the video encoding method comprising:

• receiving video data comprising a plurality of blocks including a current block;
• identifying an intra prediction mode for the current block;
• determining whether to change the intra prediction mode when deriving a transform set index;
• deriving the transform set index for the current block based on the intra prediction mode and the determination as to whether to change the intra prediction mode;
• selecting a first transform set from a plurality of transform sets according to the transform set index;
• and
• encoding the current block using the first transform set, wherein the video bitstream comprises the encoded current block and an indicator indicating whether to change the intra prediction mode.