Microsoft IMA ADPCM - Revision history

Lord Nightmare: Undo revision 15329 by Lord Nightmare (talk)

2017-10-30T06:23:41Z

Undo revision 15329 by Lord Nightmare (talk)

← Older revision		Revision as of 23:23, 29 October 2017
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	* Company: [[Microsoft]]		* Company: [[Microsoft]]
	* wFormatTag ID: WAVE_FORMAT_DVI_ADPCM		* wFormatTag ID: WAVE_FORMAT_DVI_ADPCM
			* 'short' ID: DVI_ADPCM
	* ACM Codec: 'imaadp32.acm' (included in Windows 95+)		* ACM Codec: 'imaadp32.acm' (included in Windows 95+)

Lord Nightmare: there's no point in storing both the short and long ID, the short ID is just the long id with WAVE_FORMAT removed...

2017-10-30T06:22:40Z

there's no point in storing both the short and long ID, the short ID is just the long id with WAVE_FORMAT removed...

← Older revision		Revision as of 23:22, 29 October 2017
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	* Company: [[Microsoft]]		* Company: [[Microsoft]]
	* wFormatTag ID: WAVE_FORMAT_DVI_ADPCM		* wFormatTag ID: WAVE_FORMAT_DVI_ADPCM
	* 'short' ID: DVI_ADPCM
	* ACM Codec: 'imaadp32.acm' (included in Windows 95+)		* ACM Codec: 'imaadp32.acm' (included in Windows 95+)

Lord Nightmare: add acm, wformattag and short id

2017-10-30T06:21:07Z

add acm, wformattag and short id

← Older revision		Revision as of 23:21, 29 October 2017
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	* FOURCC: 'm', 's', 0x00, 0x11		* FOURCC: 'm', 's', 0x00, 0x11
	* Company: [[Microsoft]]		* Company: [[Microsoft]]
			* wFormatTag ID: WAVE_FORMAT_DVI_ADPCM
			* 'short' ID: DVI_ADPCM
			* ACM Codec: 'imaadp32.acm' (included in Windows 95+)

	A Microsoft media file (this includes [[Microsoft Wave\|WAV]], [[Microsoft Audio/Video Interleaved\|AVI]], and [[Microsoft Advanced Streaming Format\|ASF]]) that is encoded with [[IMA ADPCM]] data has an audio format number of 0x11. The file will have a [[WAVEFORMATEX]] structure in its header which contains a field named nBlockAlign. This field reveals the size of a block of IMA-encoded data.		A Microsoft media file (this includes [[Microsoft Wave\|WAV]], [[Microsoft Audio/Video Interleaved\|AVI]], and [[Microsoft Advanced Streaming Format\|ASF]]) that is encoded with [[IMA ADPCM]] data has an audio format number of 0x11. The file will have a [[WAVEFORMATEX]] structure in its header which contains a field named nBlockAlign. This field reveals the size of a block of IMA-encoded data.

Multimedia Mike at 20:38, 4 February 2006

2006-02-04T20:38:58Z

New page

* Audio ID: 0x0011
* FOURCC: 'm', 's', 0x00, 0x11
* Company: [[Microsoft]]

A Microsoft media file (this includes [[Microsoft Wave|WAV]], [[Microsoft Audio/Video Interleaved|AVI]], and [[Microsoft Advanced Streaming Format|ASF]]) that is encoded with [[IMA ADPCM]] data has an audio format number of 0x11. The file will have a [[WAVEFORMATEX]] structure in its header which contains a field named nBlockAlign. This field reveals the size of a block of IMA-encoded data.

Note that Microsoft IMA data can also occur in Apple Quicktime files using the fourcc 'msx0x11'. In this case, a [[WAVEFORMATEX]] header will be attached to the Quicktime file's audio stsd atom.

If the IMA data is monaural, an individual chunk of data begins with the following preamble:

bytes 0-1: initial predictor (in little-endian format)
byte 2: initial index
byte 3: unknown, usually 0 and is probably reserved

The remaining bytes in the chunk are the IMA nibbles. Each byte is decoded bottom nibble first, then top nibble as follows:

byte0 byte1 byte2 byte3 ...
n1n0 n3n2 n5n4 n7n6 ...

If the IMA data is stereo, a chunk begins with two preambles, one for the left audio channel and one for the right channel:

bytes 0-1: initial predictor (in little-endian format) for left channel
byte 2: initial index for left channel
byte 3: unknown, usually 0 and is probably reserved
bytes 4-5: initial predictor (in little-endian format) for right channel
byte 6: initial index (for right channel)
byte 7: unknown, usually 0 and is probably reserved

The remaining bytes in the chunk are the IMA nibbles. The first 4 bytes, or 8 nibbles, belong to the left channel and the next 4 bytes belong to the right channel. This interleaving continues until the end of the chunk:

byte0 byte1 byte2 byte3 ...
n1n0 n3n2 n5n4 n7n6 ...(left channel)
byte4 byte5 byte6 byte7 ...
n1n0 n3n2 n5n4 n7n6 ...(right channel)

[[Category:Audio Codecs]]
[[Category:ADPCM Audio Codecs]]
[[Category:IMA ADPCM Audio Codecs]]