Xan DPCM - Revision history

Matt: add fourcc to header

2021-03-01T01:45:56Z

add fourcc to header

← Older revision		Revision as of 18:45, 28 February 2021
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	Company: [[Origin Systems]]		* FourCC: Axan
			* Company: [[Origin Systems]]

	Origin's [http://www.mobygames.com/game/dos/wing-commander-iv-the-price-of-freedom Wing Commander IV: The Price of Freedom] and Crusader: No Regret computer games transport multimedia cutscenes in standard Microsoft [[Microsoft Audio/Video Interleaved\|AVI]] files. The video in the files is encoded in the [[Origin Xan Codec]] format, and the audio is encoded using a custom format that this page takes the liberty of naming Xan DPCM.		Origin's [http://www.mobygames.com/game/dos/wing-commander-iv-the-price-of-freedom Wing Commander IV: The Price of Freedom] and Crusader: No Regret computer games transport multimedia cutscenes in standard Microsoft [[Microsoft Audio/Video Interleaved\|AVI]] files. The video in the files is encoded in the [[Origin Xan Codec]] format, and the audio is encoded using a custom format that this page takes the liberty of naming Xan DPCM.

Matt at 01:42, 1 March 2021

2021-03-01T01:42:41Z

← Older revision		Revision as of 18:42, 28 February 2021
Line 3:		Line 3:
	Origin's [http://www.mobygames.com/game/dos/wing-commander-iv-the-price-of-freedom Wing Commander IV: The Price of Freedom] and Crusader: No Regret computer games transport multimedia cutscenes in standard Microsoft [[Microsoft Audio/Video Interleaved\|AVI]] files. The video in the files is encoded in the [[Origin Xan Codec]] format, and the audio is encoded using a custom format that this page takes the liberty of naming Xan DPCM.		Origin's [http://www.mobygames.com/game/dos/wing-commander-iv-the-price-of-freedom Wing Commander IV: The Price of Freedom] and Crusader: No Regret computer games transport multimedia cutscenes in standard Microsoft [[Microsoft Audio/Video Interleaved\|AVI]] files. The video in the files is encoded in the [[Origin Xan Codec]] format, and the audio is encoded using a custom format that this page takes the liberty of naming Xan DPCM.

	~~Note~~ that an AVI file demuxer will probably need to be modified to support the algorithm. The [[WAVEFORMATEX]] headers in the Xan AVI files report the audio coding as format 0x0001: [[PCM]]. However, the file's 'auds' chunk begins with the fourcc 'Axan'. A program can either check for this or assume that the file uses Xan DPCM if it uses [[Origin Xan Codec\|Xan]] video.		For the Wing Commander IV AVIs, note that an AVI file demuxer will probably need to be modified to support the algorithm. The [[WAVEFORMATEX]] headers in the Xan AVI files report the audio coding as format 0x0001: [[PCM]]. However, the file's 'auds' chunk begins with the fourcc 'Axan'. A program can either check for this or assume that the file uses Xan DPCM if it uses [[Origin Xan Codec\|Xan]] video. In Crusader: No Regret's AVIs the chunk also begins with 'Axan', but the format is set as 0x594a. The decoding method is the same.

	Classifying the Xan audio coding method as a DPCM algorithm is a little shaky. It actually resembles a cross between a DPCM algorithm and a APDCM algorithm. Perhaps the designers could not decide between the two algorithm families and decided to split the difference. The algorithm encodes 16-bit PCM samples as 8-bit bytes by packing a 6-bit delta value along with a 2-bit delta modifier into a byte.		Classifying the Xan audio coding method as a DPCM algorithm is a little shaky. It actually resembles a cross between a DPCM algorithm and a APDCM algorithm. Perhaps the designers could not decide between the two algorithm families and decided to split the difference. The algorithm encodes 16-bit PCM samples as 8-bit bytes by packing a 6-bit delta value along with a 2-bit delta modifier into a byte.

Matt: Mention that this format is used in Crusader: No Regret, and link to video codec.

2021-03-01T01:37:42Z

Mention that this format is used in Crusader: No Regret, and link to video codec.

← Older revision		Revision as of 18:37, 28 February 2021
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	Company: [[Origin Systems]]		Company: [[Origin Systems]]

	Origin's [http://www.mobygames.com/game/dos/wing-commander-iv-the-price-of-freedom Wing Commander IV: The Price of Freedom] computer ~~game transports~~ multimedia cutscenes in standard Microsoft [[Microsoft Audio/Video Interleaved\|AVI]] files. The ~~audio~~ in ~~these~~ files is encoded using a custom format that this page takes the liberty of naming Xan DPCM.		Origin's [http://www.mobygames.com/game/dos/wing-commander-iv-the-price-of-freedom Wing Commander IV: The Price of Freedom] and Crusader: No Regret computer games transport multimedia cutscenes in standard Microsoft [[Microsoft Audio/Video Interleaved\|AVI]] files. The video in the files is encoded in the [[Origin Xan Codec]] format, and the audio is encoded using a custom format that this page takes the liberty of naming Xan DPCM.

	Note that an AVI file demuxer will probably need to be modified to support the algorithm. The [[WAVEFORMATEX]] headers in the Xan AVI files report the audio coding as format 0x0001: [[PCM]]. However, the file's 'auds' chunk begins with the fourcc 'Axan'. A program can either check for this or assume that the file uses Xan DPCM if it uses [[Origin Xan Codec\|Xan]] video.		Note that an AVI file demuxer will probably need to be modified to support the algorithm. The [[WAVEFORMATEX]] headers in the Xan AVI files report the audio coding as format 0x0001: [[PCM]]. However, the file's 'auds' chunk begins with the fourcc 'Axan'. A program can either check for this or assume that the file uses Xan DPCM if it uses [[Origin Xan Codec\|Xan]] video.

Avenger teambg at 10:18, 11 April 2007

2007-04-11T10:18:22Z

← Older revision		Revision as of 03:18, 11 April 2007
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	byte = next byte in stream		byte = next byte in stream
	diff = (byte		diff = (byte & 0xFC) << 8
			if bottom 2 bits of byte are both 1 (byte & 0x03)
			shifter++
			else
			shifter -= (2 * (byte & 3))
			note that the shift value may not go below 0 and must be saturated here
			shift diff right by shifter value
			apply diff to the current predictor
			saturate predictor to signed, 16-bit range

			Note that diff must be treated as a signed 16-bit number. For stereo data, the bytes represent interleaved samples in LRLR order.

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

Ek1Mpj at 06:49, 11 April 2007

2007-04-11T06:49:02Z

← Older revision		Revision as of 23:49, 10 April 2007
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	byte = next byte in stream		byte = next byte in stream
	diff = (byte ~~& 0xFC) << 8~~		diff = (byte
	~~if bottom 2 bits of byte are both 1 (byte & 0x03)~~
	~~shifter++~~
	~~else~~
	~~shifter -= (2 * (byte & 3))~~
	~~note that the shift value may not go below 0 and must be saturated here~~
	~~shift diff right by shifter value~~
	~~apply diff to the current predictor~~
	~~saturate predictor to signed, 16-bit range~~

	~~Note that diff must be treated as a signed 16-bit number. For stereo data, the bytes represent interleaved samples in LRLR order.~~

	~~[[Category:Audio Codecs]]~~
	~~[[Category:DPCM Audio Codecs]]~~
	~~[[Category:Game Formats]]~~

Multimedia Mike: also a game format

2006-02-05T07:11:47Z

also a game format

← Older revision		Revision as of 00:11, 5 February 2006
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	Note that diff must be treated as a signed 16-bit number. For stereo data, the bytes represent interleaved samples in LRLR order.		Note that diff must be treated as a signed 16-bit number. For stereo data, the bytes represent interleaved samples in LRLR order.

			[[Category:Audio Codecs]]
	[[Category:DPCM Audio Codecs]]		[[Category:DPCM Audio Codecs]]
	[[Category:~~Audio Codecs~~]]		[[Category:Game Formats]]

Multimedia Mike: associate a company

2006-02-05T02:06:21Z

associate a company

← Older revision		Revision as of 19:06, 4 February 2006
Line 1:		Line 1:
			Company: [[Origin Systems]]

	Origin's [http://www.mobygames.com/game/dos/wing-commander-iv-the-price-of-freedom Wing Commander IV: The Price of Freedom] computer game transports multimedia cutscenes in standard Microsoft [[Microsoft Audio/Video Interleaved\|AVI]] files. The audio in these files is encoded using a custom format that this page takes the liberty of naming Xan DPCM.		Origin's [http://www.mobygames.com/game/dos/wing-commander-iv-the-price-of-freedom Wing Commander IV: The Price of Freedom] computer game transports multimedia cutscenes in standard Microsoft [[Microsoft Audio/Video Interleaved\|AVI]] files. The audio in these files is encoded using a custom format that this page takes the liberty of naming Xan DPCM.

DonDiego: Add to audio codecs category.

2006-02-05T01:36:36Z

Add to audio codecs category.

← Older revision		Revision as of 18:36, 4 February 2006
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	[[Category:DPCM Audio Codecs]]		[[Category:DPCM Audio Codecs]]
			[[Category:Audio Codecs]]

Multimedia Mike at 19:54, 4 February 2006

2006-02-04T19:54:13Z

New page

Origin's [http://www.mobygames.com/game/dos/wing-commander-iv-the-price-of-freedom Wing Commander IV: The Price of Freedom] computer game transports multimedia cutscenes in standard Microsoft [[Microsoft Audio/Video Interleaved|AVI]] files. The audio in these files is encoded using a custom format that this page takes the liberty of naming Xan DPCM.

Note that an AVI file demuxer will probably need to be modified to support the algorithm. The [[WAVEFORMATEX]] headers in the Xan AVI files report the audio coding as format 0x0001: [[PCM]]. However, the file's 'auds' chunk begins with the fourcc 'Axan'. A program can either check for this or assume that the file uses Xan DPCM if it uses [[Origin Xan Codec|Xan]] video.

Classifying the Xan audio coding method as a DPCM algorithm is a little shaky. It actually resembles a cross between a DPCM algorithm and a APDCM algorithm. Perhaps the designers could not decide between the two algorithm families and decided to split the difference. The algorithm encodes 16-bit PCM samples as 8-bit bytes by packing a 6-bit delta value along with a 2-bit delta modifier into a byte.

For each chunk of Xan DPCM data, the first 2 or 4 bytes are the initial predictors for that chunk, depending on mono or stereo data, and are encoded as signed, 16-bit, little-endian numbers. A shifter value for each channel is initialized to 4. For each byte in the stream (assuming mono data):

byte = next byte in stream
diff = (byte & 0xFC) << 8
if bottom 2 bits of byte are both 1 (byte & 0x03)
shifter++
else
shifter -= (2 * (byte & 3))
note that the shift value may not go below 0 and must be saturated here
shift diff right by shifter value
apply diff to the current predictor
saturate predictor to signed, 16-bit range

Note that diff must be treated as a signed 16-bit number. For stereo data, the bytes represent interleaved samples in LRLR order.

[[Category:DPCM Audio Codecs]]