Decoder derived cross component prediction in video coding

1 . A method of decoding video data, the method comprising:

receiving a first instance of a flag for a first block, wherein a first value for the flag indicates that a cross-component prediction (CCP) mode is derived without signaling of the CCP mode and a second value for the flag indicates that the CCP mode is signaled;

in response to determining that the first instance of the flag is set to the first value, deriving a first CCP mode for the first block;

determining a first predicted chroma block for the first block using the first CCP mode;

receiving a second instance of the flag for a second block;

in response to determining that the second instance of the flag is set to the second value, receiving additional signaling;

determining a second CCP mode for the second block based on the additional signaling identifying the second CCP mode;

determining a second predicted chroma block for the second block using the second CCP mode;

determining a decoded version of the first block based on the first predicted chroma block;

determining a decoded version of the second block based on the second predicted chroma block; and

outputting one or more pictures of decoded video data, wherein the decoded video data includes the decoded version of the first block and the decoded version of the second block.

2 . The method of claim 1 , wherein deriving the first CCP mode for the first block comprises:

determining a list of candidate CCP modes; and

selecting the first CCP mode from the list of candidate CCP modes.

3 . The method of claim 2 , wherein deriving the first CCP mode for the first block further comprises:

determining template costs for the candidate CCP modes; and

selecting the first CCP mode from the list of candidate CCP modes based on the template costs.

4 . The method of claim 2 , further comprising:

determining the list of candidate CCP modes based on a slice type of a slice that includes the first block.

5 . The method of claim 2 , wherein the list of candidate CCP modes includes a first candidate CCP mode that utilizes a top-and-left template and a second candidate CCP mode that utilizes one of a left-only template or a top-only template.

6 . The method of claim 2 , wherein the list of candidate CCP modes includes a cross-component linear model prediction mode and a cross-component intra prediction mode.

7 . The method of claim 2 , further comprising:

adding one or more fusion modes to the list of candidate CCP modes based on a size of the first block.

8 . The method of claim 1 , wherein one or both of the first CCP mode and the second CCP mode comprise a fusion mode.

9 . The method of claim 1 , wherein the flag comprises a block-level flag.

10 . A device for decoding video data, the device comprising: a memory configured to store video data; and one or more processors implemented in circuitry and configured to:

receive a first instance of a flag for a first block, wherein a first value for the flag indicates that a cross-component prediction (CCP) mode is derived without signaling of the CCP mode and a second value for the flag indicates that the CCP mode is signaled;

in response to determining that the first instance of the flag is set to the first value, derive a first CCP mode for the first block;

determine a first predicted chroma block for the first block using the first CCP mode;

receive a second instance of the flag for a second block;

in response to determining that the second instance of the flag is set to the second value, receive additional signaling;

determine a second CCP mode for the second block based on the additional signaling identifying the second CCP mode;

determine a second predicted chroma block for the second block using the second CCP mode;

determine a decoded version of the first block based on the first predicted chroma block;

determine a decoded version of the second block based on the second predicted chroma block; and

output one or more pictures of decoded video data, wherein the decoded video data includes the decoded version of the first block and the decoded version of the second block.

11 . The device of claim 10 , wherein to derive the first CCP mode for the first block, the one or more processors are further configured to:

determine a list of candidate CCP modes; and

select the first CCP mode from the list of candidate CCP modes.

12 . The device of claim 11 , wherein to derive the first CCP mode for the first block, the one or more processors are further configured to:

determine template costs for the candidate CCP modes; and

select the first CCP mode from the list of candidate CCP modes based on the template costs.

13 . The device of claim 11 , wherein the one or more processors are further configured to:

determine the list of candidate CCP modes based on a slice type of a slice that includes the first block.

14 . The device of claim 11 , wherein the list of candidate CCP modes includes a first candidate CCP mode that utilizes a top-and-left template and a second candidate CCP mode that utilizes one of a left-only template or a top-only template.

15 . The device of claim 11 , wherein the list of candidate CCP modes includes a cross-component linear model prediction mode and a cross-component intra prediction mode.

16 . The device of claim 11 , wherein the one or more processors are further configured to:

add one or more fusion modes to the list of candidate CCP modes based on a size of the first block.

17 . The device of claim 10 , wherein one or both of the first CCP mode and the second CCP mode comprise a fusion mode.

18 . The device of claim 10 , wherein the flag comprises a block-level flag.

19 . The device of claim 10 , further comprising a display configured to display the one or more pictures of decoded video data.

20 . The device of claim 10 , wherein the device comprises one or more of a camera, a computer, a mobile device, a broadcast receiver device, or a set-top box.

21 . A method of encoding video data, the method comprising:

deriving a first CCP mode for a first block;

transmitting, in encoded video data, a first instance of a flag for a first block, wherein a first value for the flag indicates that a cross-component prediction (CCP) mode is derived without signaling of the CCP mode and a second value for the flag indicates that the CCP mode is signaled;

determining a second CCP mode for a second block;

transmitting, in the encoded video data, a second instance of the flag for a second block; and

in response to transmitting the second instance of the flag set to the second value, transmitting, in the encoded video data, one or more additional syntax elements identifying the second CCP mode.

22 . The method of claim 21 , wherein deriving the first CCP mode for the first block comprises:

determining a list of candidate CCP modes; and

selecting the first CCP mode from the list of candidate CCP modes.

23 . The method of claim 22 , wherein deriving the first CCP mode for the first block further comprises:

determining template costs for the candidate CCP modes; and

selecting the first CCP mode from the list of candidate CCP modes based on the template costs.

24 . The method of claim 22 , further comprising:

determining the list of candidate CCP modes based on a slice type of a slice that includes the first block.

25 . A device for encoding video data, the device comprising:

a memory configured to store video data; and one or more processors implemented in circuitry and configured to:

derive a first CCP mode for a first block;

transmit, in encoded video data, a first instance of a flag for a first block, wherein a first value for the flag indicates that a cross-component prediction (CCP) mode is derived without signaling of the CCP mode and a second value for the flag indicates that the CCP mode is signaled;

determine a second CCP mode for a second block;

transmit, in the encoded video data, a second instance of the flag for a second block; and

in response to transmitting the second instance of the flag set to the second value, transmit, in the encoded video data, one or more additional syntax elements identifying the second CCP mode.

26 . The device of claim 25 , wherein deriving the first CCP mode for the first block comprises:

determining a list of candidate CCP modes; and

selecting the first CCP mode from the list of candidate CCP modes.

27 . The device of claim 26 , wherein to derive the first CCP mode for the first block, the one or more processors are further configured to:

determine template costs for the candidate CCP modes; and

select the first CCP mode from the list of candidate CCP modes based on the template costs.

28 . The device of claim 26 , wherein the one or more processors are further configured to:

determine the list of candidate CCP modes based on a slice type of a slice that includes the first block.

29 . The device of claim 25 , wherein the flag comprises a block-level flag.

30 . The device of claim 25 , further comprising: a camera configured to acquire the video data.