Adaptive entropy encoding and decoding techniques are described. For example, a screen capture encoder and decoder perform adaptive entropy encoding and decoding of palettized screen capture content in screen capture video. The encoder selects between different entropy encoding modes (such as an arithmetic coding mode and a combined run length/Huffman encoding mode, which allow the encoder to emphasize bitrate reduction at some times and encoding speed at other times). The run length encoding can use run value symbols adapted to common patterns of redundancy in the content. When the encoder detects series of pixels that could be encoded with different, alternative runs, the encoder selects between the alternative runs based upon efficiency criteria. The encoder also performs adaptive Huffman encoding, efficiently parameterizing Huffman code tables to reduce overall bitrate while largely preserving the compression gains of the adaptive Huffman encoding. A decoder performs converse operations.