Extended multiple transform selection for video coding

A device for transforming a block of video data, the device comprising:

• a memory configured to store video data;
• and
• one or more processors implemented in circuitry and configured to:
• code a value for a low frequency non-separable transform (LFNST) index (LFNST_idx) syntax element for a current block of video data, the value for the LFNST_idx syntax element being non-zero and indicating a secondary transform for the current block of video data;
• determine that a multiple transform selection (MTS) scheme for the current block of video data indicates a discrete cosine transform 2 (DCT-2) primary transform for the current block of video data;
• and
• apply the DCT-2 primary transform and the secondary transform during coding of residual data for the current block of video data.

A computer-readable storage medium having stored thereon instructions that, when executed, cause a processor to:

• code a value for a low frequency non-separable transform (LFNST) index (LFNST_idx) syntax element for a current block of video data, the value for the LFNST_idx syntax element being non-zero and indicating a secondary transform for the current block of video data;
• determine that a multiple transform selection (MTS) scheme for the current block of video data indicates a discrete cosine transform 2 (DCT-2) primary transform for the current block of video data;
• and
• apply the DCT-2 primary transform and the secondary transform during coding of residual data for the current block of video data.

A device for transforming a block of video data, the device comprising:

• means for coding a value for a low frequency non-separable transform (LFNST) index (LFNST_idx) syntax element for a current block of video data, the value for the LFNST_idx syntax element being non-zero and indicating a secondary transform for the current block of video data;
• means for determining that a multiple transform selection (MTS) scheme for the current block of video data indicates a discrete cosine transform 2 (DCT-2) primary transform for the current block of video data;
• and
• means for applying the DCT-2 primary transform and the secondary transform during coding of residual data for the current block of video data.