DVI IMA ADPCM

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According to the XAnim multimedia application, there are two variants of DVI IMA ADPCM, both of which are encoded and decoded with the IMA ADPCM algorithm. The original variant encodes the top nibble of a byte first, then the bottom nibble. The revised variant has the opposite encoding order.

IMA ADPCM and Microsoft IMA ADPCM are both the same codec, an implementation of the Intel/DVI(R) IMA ADPCM standard, the only difference being encapsulation around (and nybble order of) the ADPCM data. The IMA ADPCM standard did not specify headers (RIFF/WAV/AU/etc) nor did it specify a nybble order for packing 4-bit ADPCM nybbles to a byte, while the Microsoft IMA ADPCM implementation does. It is possible that other IMA ADPCM implementations, such as the one in .AU and .AIFF files, is different in this regard.