Context modeling for low-frequency non-separable transformation signaling for video coding

A method of encoding video data, the method comprising:

• selecting, from a plurality of low-frequency non-separable transforms (LFNSTs), a LFNST having an LFNST index;
• transforming, using the LFNST, transform coefficients of a unit of video data;
• determining a color component of the unit of video data;
• determining, based at least on the color component, a context for context-adaptive binary arithmetic coding (CABAC) a syntax element that specifies the value of the LFNST index for the unit of video data;
• and
• CABAC encoding, based on the determined context and via a syntax structure for the unit of video data, the syntax element that specifies the value of the LFNST index for the unit of video data.

A device for coding video data, the device comprising:

• a memory;
• and
• one or more processors implemented in circuitry and configured to:
• determine a color component of a unit of video data;
• determine, based at least on the color component, a context for context-adaptive binary arithmetic coding (CABAC) a syntax element that specifies a value of a low-frequency non-separable transform (LFNST) index for the unit of video data;
• CABAC code, based on the determined context and via a syntax structure for the unit of video data, the syntax element that specifies the value of the LFNST index for the unit of video data;
• and
• transform, based on a transform indicated by the value of the LFNST index, transform coefficients of the unit of video data.