A video encoder divides a picture into a plurality of picture partitions, such as tiles or wavefront parallel processing (WPP) waves. The picture partitions are associated with non-overlapping subsets of the treeblocks of the picture. The video encoder generates a coded slice network abstraction layer (NAL) unit that includes encoded representations of the treeblocks associated with a slice of the picture. The coded treeblocks are grouped within the coded slice NAL unit into segments associated with different ones of the picture partitions. The video encoder pads one or more of the segments such that each of the segments begins on a byte boundary.