Rules for intra-picture prediction modes when wavefront parallel processing is enabled

A computer system comprising a processor and memory, the computer system implementing a video encoder configured to perform operations comprising:

• determining that wavefront parallel processing (“WPP”) is enabled;
• outputting, as part of data in a bitstream, a flag that indicates whether or not WPP is enabled, the flag being part of a picture parameter set syntax structure or sequence parameter set syntax structure in the bitstream;
• and
• encoding a picture, including, for a palette coding mode, predicting a palette for an initial unit in a current WPP row of the picture using previous palette data from a previous unit in a previous WPP row of the picture, wherein the previous WPP row is immediately above the current WPP row, the previous unit in the previous WPP row being above the initial unit in the current WPP row, wherein the previous palette data from the previous unit in the previous WPP row includes, for each of C colors, one or more color component values, and wherein C is limited by a threshold count for the previous palette data from the previous unit in the previous WPP row.

One or more non-transitory computer-readable media having stored thereon data as part of a bitstream, wherein the data includes a flag that indicates whether or not wavefront parallel processing (“WPP”) is enabled, the flag being part of a picture parameter set syntax structure or sequence parameter set syntax structure, wherein the data further includes encoded data for one or more slices of a picture, and wherein the data is usable to cause a video decoder, when processing the data in a computer system having one or more processing units and memory, to perform operations comprising:

• determining, based on the flag, that WPP is enabled;
• and
• reconstructing the picture based at least in part on the encoded data for the one or more slices of the picture, including, for a palette decoding mode, predicting a palette for an initial unit in a current WPP row of the picture using previous palette data from a previous unit in a previous WPP row of the picture, wherein the previous WPP row is immediately above the current WPP row, the previous unit in the previous WPP row being above the initial unit in the current WPP row, wherein the previous palette data from the previous unit in the previous WPP row includes, for each of C colors, one or more color component values, and wherein C is limited by a threshold count for the previous palette data from the previous unit in the previous WPP row.