1. A device for coding video data, the device comprising: a memory configured to store a plurality of separable transforms for use in transforming between residual pixel values of a video block and residual transform coefficients of the video block, each of the plurality of separable transforms being associated with a corresponding partition size, wherein the plurality of separable transforms each comprise a column transform matrix of size N×N and a row transform matrix of size N×N, where N×N is a dimension of a partition size of a predicted video block; and a processor configured to: generate predicted pixel values of a video block having a partition size based on a prediction mode, wherein the prediction mode comprises one of a plurality of prediction modes for predicting pixel values in a specified direction; select, based on the prediction mode, one or more separable transforms from the plurality of separable transforms for the partition size, wherein for a first one of the prediction modes having a first prediction direction and a second one of the prediction modes having a second, different, prediction direction, different transforms are selected based on the prediction mode, and wherein, for the first one of the prediction modes, selecting the one or more separable transforms comprises selecting a combination of a separable DCT transform and at least one other different separable transform; and apply the selected separable transforms to transform between residual pixel values associated with the predicted pixel values and residual transform coefficients.