CRYO APC

2007-04-10T19:01:57Z

MlzIy5:

* Extensions: .APC, .HNM, .BF, .ZIK
* Company: [[CRYO Interactive Entertainment]]

This covers the audio format for one of the versions of CRYO's video formats.

==Credit==
This file comes from [http://www.wotsit.org wotsit.org] and was originally written by Valery V. Anisimovsky.

== APC Audio Files==

The music, sfx, speech and video (.HNM) soundtracks in some CRYO Interactive
games are .APC stand-alone files. APC file has the following header:

struct APCHeader
{
char szID[8];
char szVersion[4];
DWORD dwOutSize;
DWORD dwSampleRate;
LONG lSampleLeft;
LONG lSampleRight;
DWORD dwStereo;
};

''szID'' -- ID string, which is "CRYO_APC".

''szVersion'' -- version ID string, all files in the mentioned games have this
set to "1.20". Note that this field may, in principle, vary.

''dwOutSize'' -- number of samples in the file. May be used for song length
(in seconds) calculation.

''dwSampleRate'' -- sample rate for the file.

''lSampleLeft'' -- the initial value for the left sample (see below).

''lSampleRight'' -- the initial value for the right sample (see below).

''dwStereo'' -- this seems to be boolean stereo flag: if this is not zero, the
audio stream in the file is stereo (music and partly video soundtracks),
otherwise it's mono (sfx, speech).

The resolution is NOT specified in the header, so the default value (16-bit)
should be used.

After the APCHeader IMA ADPCM compressed sound data comes. You may find
IMA ADPCM decompression scheme description further in this document.

== IMA ADPCM Decompression Algorithm ==

During the decompression four LONG variables must be maintained for stereo
stream: ''lIndexLeft, lIndexRight, lCurSampleLeft, lCurSampleRight'' and two --
for mono stream: ''lIndex, lCurSample''. At the beginning of the file you must
initialize ''lCurSampleLeft/Right'' variables to the values from APCHeader while
''lIndexLeft/Right'' are initialized to zeroes.
Note that LONG here is signed.

Here's the code which decompresses one byte of IMA ADPCM compressed
stereo stream. Other bytes are processed in the same way.

BYTE Input; // current byte of compressed data
BYTE Code;
LONG Delta;

Code=HINIBBLE(Input); // get HIGHER 4-bit nibble

Delta=StepTable[lIndexLeft]>>3;
if (Code

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CRYO APC