Kostya: fill at least some details

2023-08-28T14:56:37Z

fill at least some details

← Older revision		Revision as of 07:56, 28 August 2023
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	* Samples: http://samples.mplayerhq.hu/game-formats/interplay-acmp/		* Samples: http://samples.mplayerhq.hu/game-formats/interplay-acmp/

	Interplay ACMP is an audio compression file format used in some games from Interplay. The ~~specific audio coding format~~ is ~~presently unknown but is suspected to be~~ [[~~ACOMP~~]].		Interplay ACMP is an audio compression file format used in some games from Interplay. The name is shortened "AUDCOMP" and it employs [[DPCM]] with variable-length coding for compressing 8-bit PCM.

	== Interplay ACMP Format ==		== Interplay ACMP Format ==
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	bytes 26-29 possibly the size of decompressed audio		bytes 26-29 possibly the size of decompressed audio
	bytes 30.. suspected to be the encoded audio data		bytes 30.. suspected to be the encoded audio data

			== Audio data coding ==
			Audio seems to be coded in blocks of 256 samples (or less for the last block). Each block starts with 8-bit header:
			* 1 bit - audio is transformed and only half of the samples are transmitted;
			* 2 bits - quantisation step
			* 5 bits - coding mode (0-6)

			In general, block data is compressed by first taking differences (initial value is 0x80), quantising it by discarding low bits and coding in one of several ways. Some encoding modes use so-called tally code which is an unary code for <code>min(value, 10)</code> and with optional 6-bit full value written afterwards (for values 10 and above). Also deltas are often coded as absolute values with a sign bit following.

			Coding modes are:
			* 0 - constant block, first sample is coded as is;
			* 1 - deltas are coded as <code>tally(ilog2(\|delta\|)) \|delta\| sign</code> (or <code>tally(1)</code> for zero delta);
			* 2 - deltas are coded as 4-bit fields, those that do not fit coded as 0 nibble plus <code>8 - quant_bits</code> bits for the actual delta value;
			* 3 - deltas are coded as <code>tally((\|diff\| >> 2) + 1) \|diff\|&3 sign</code>;
			* 4 - the same as previous but with 3 low bits coded raw;
			* 5 - delta 0 is coded as <code>00</code>, delta 1 is coded as <code>01</code>, other deltas are coded as <code>10 tally(ilog2(\|diff\| - 1)) (\|diff\| - 1) sign</code>;
			* 6 - simply write raw quantised differences using <code>8 - quant_bits</code> bits for each.

	== Games Using Interplay ACMP Files ==		== Games Using Interplay ACMP Files ==
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	[[Category:Audio Codecs]]		[[Category:Audio Codecs]]
	[[Category:Game Formats]]		[[Category:Game Formats]]
	[[Category:~~Undiscovered~~ Audio Codecs]]		[[Category:Incomplete Audio Codecs]]

Multimedia Mike: correct categories

2011-07-12T05:04:44Z

correct categories

← Older revision		Revision as of 22:04, 11 July 2011
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	[[Category:Audio Codecs]]		[[Category:Audio Codecs]]
	[[Category:Game Formats]]		[[Category:Game Formats]]
	[[Category:Undiscovered ~~Formats~~]]		[[Category:Undiscovered Audio Codecs]]

Multimedia Mike at 05:02, 12 July 2011

2011-07-12T05:02:34Z

New page

* Company: [[Interplay Entertainment]]
* Samples: http://samples.mplayerhq.hu/game-formats/interplay-acmp/

Interplay ACMP is an audio compression file format used in some games from Interplay. The specific audio coding format is presently unknown but is suspected to be [[ACOMP]].

== Interplay ACMP Format ==
Multi-byte numbers are stored in big endian format.

bytes 0-19 Signature string: 'Interplay ACMP Data\x1A'
bytes 20-21 sample rate
bytes 22-23 unknown, always seems to be 0 and might be part of sample rate
byte 24 unknown, always seems to be 0x28
byte 25 unknown, always seems to be 0
bytes 26-29 possibly the size of decompressed audio
bytes 30.. suspected to be the encoded audio data

== Games Using Interplay ACMP Files ==
* [http://www.mobygames.com/game/star-trek-judgment-rites Star Trek: Judgment Rites]

[[Category:Audio Codecs]]
[[Category:Game Formats]]
[[Category:Undiscovered Formats]]

Interplay ACMP - Revision history

Kostya: fill at least some details

Multimedia Mike: correct categories

Multimedia Mike at 05:02, 12 July 2011