Extended multiple transform selection for video coding

A device for coding video data, the device comprising:

• a memory configured to store video data;
• and
• one or more processors implemented in circuitry and configured to:
• determine that a first codeword representing a selected transform scheme of a set of transform candidates of a multiple transform selection (MTS) scheme for a current block of the video data has a value indicating that a discrete cosine transform 2 (DCT-2) primary transform is to be applied to the current block;
• code a second codeword representing a secondary transform from a set of available secondary transforms to be applied to the current block when the first codeword has the value indicating that the DCT-2 primary transform is to be applied to the current block;
• and
• apply the DCT-2 primary transform and the secondary transform during coding of residual data for the current block.

A device for coding video data, the device comprising:

• means for determing that a first codeword representing a selected transform scheme of a set of transform candidates of a multiple transform selection (MTS) scheme for a current block of video data has a value indicating that a discrete cosine transform 2 (DCT-2) primary transform is to be applied to the current block;
• means for coding a second codeword representing a secondary transform from a set of available secondary transforms to be applied to the current block when the first codeword has the value indicating that the DCT-2 primary transform is to be applied to the current block;
• and
• means for applying the DCT-2 primary transform and the secondary transform during coding of residual data for the current block.

A non-transitory computer-readable storage medium having stored thereon instructions that, when executed, cause a processor of a device for coding video data to:

• determine that a first codeword representing a selected transform scheme of a set of transform candidates of a multiple transform selection (MTS) scheme for a current block of video data has a value indicating that a discrete cosine transform 2 (DCT-2) primary transform is to be applied to the current block;
• code a second codeword representing a secondary transform from a set of available secondary transforms when the first codeword has the value indicating that the DCT-2 primary transform is to be applied to the current block;
• and
• apply the DCT-2 primary transform and the secondary transform during coding of residual data for the current block.