1. An apparatus comprising: a memory having stored therein at least one block of video data; and a control circuit operably coupled to the memory and configured to: determine a plurality of possible different primary prediction modes to employ when encoding the block of video data; for each primary prediction mode of the plurality of possible different primary prediction modes: determine, using a companion prediction mode lookup table, a corresponding companion prediction mode to correspond to that primary prediction mode, generate a respective mixed prediction for the block of video data by mixing a first respective prediction formed using that primary prediction mode with a second respective prediction formed using the corresponding companion prediction mode of that primary prediction mode, and following the generating of the respective mixed prediction for the block of video data, determine an efficacy metric for the respective mixed prediction, and automatically update the companion prediction mode lookup table; use the efficacy metrics to identify a selected primary prediction mode for a most efficacious one of the plurality of mixed predictions; and use the selected primary prediction mode to encode the block of video data.