Interleaving entropy codes

The paper addresses several issues involved in interleaving compressed output from multiple non-prefix codes or from a combination of prefix and non-prefix codes. The technique used throughout is decoder-synchronized encoding, in which the encoder manipulates the data stream to allow just-in-time decoding. We provide three extensions to block Melcode (a coder based on interleaved run-length codes) that allow its use with multisymbol alphabets, allow its use with an extended class of prefix codes, and reduce its worst-case inefficiency by almost two thirds. We also show that it is possible to interleave output from an arithmetic coder with output from a prefix coder, such as a Huffman coder; we present an encoder back-end that handles all the details transparently, requiring only minor changes to the encoders and no changes to the decoders.