The top two competing entropy coders at the moment are Arithmetic Coding (AC) and Asymmetrical Number Systems (ANS).
A very interesting difference between the two is that AC is FIFO and ANS is LIFO. That is, in AC the first symbol you encode into the bitstream is also the first symbol you decode. However with ANS the last symbol you encode is the first symbol you decode.
Is there a fundamental difference between these approaches? Could one be converted into the other? What are the advantages/disadvantages of the two approaches?