Flash IMA ADPCM

Flash files can contain audio data encoded with IMA ADPCM. However, the file can use a number of different predictor sizes instead of just 4 bits as in most IMA ADPCM formats. 2, 3, and 5-bit predictors are also available.

According to SWF SPEC 19 ; the 2bps index table is {-1,2, -1,2}, the 3bps index table is {-1,-1,2,4, -1,-1,2,4}, and the 5bps index table is {-1,-1,-1,-1,-1,-1,-1,-1,1,2,4,6,8,10,13,16, -1,-1,-1,-1,-1,-1,-1,-1,1,2,4,6,8,10,13,16}. The 5bps index table is not linear as it's second and fourth quarters are {1,2,4,6,8,10,13,16} instead of {2,4,6,8,10,12,14,16}.