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This structure defines the format of waveform-audio data. Only format information common to all waveform-audio data formats is included in this structure. For formats that require additional information, this structure is included as the first member in another structure, along with the additional information.
typedef struct { WORD
wFormatTag
; WORD
nChannels
; DWORD
nSamplesPerSec
; DWORD
nAvgBytesPerSec
; WORD
nBlockAlign
; WORD
wBitsPerSample
; WORD
cbSize
;} WAVEFORMATEX;
Members
- wFormatTag
- Waveform-audio format type. Format tags are registered with Microsoft Corporation for many compression algorithms. A complete list of format tags can be found in the Mmsystem.h header file.
- nChannels
- Number of channels in the waveform-audio data. Monaural data uses one channel and stereo data uses two channels.
- nSamplesPerSec
- Sample rate, in samples per second (hertz), that each channel should be played or recorded. If wFormatTagis WAVE_FORMAT_PCM, then common values for nSamplesPerSecare 8.0 kHz, 11.025 kHz, 22.05 kHz, and 44.1 kHz. For non-PCM formats, this member must be computed according to the manufacturer's specification of the format tag.
- nAvgBytesPerSec
- Required average data-transfer rate, in bytes per second, for
the format tag. If
wFormatTagis WAVE_FORMAT_PCM,
nAvgBytesPerSecshould be equal to the product of
nSamplesPerSecand
nBlockAlign. For non-PCM formats, this member must be
computed according to the manufacturer's specification of the
format tag.
Playback and record software can estimate buffer sizes by using the nAvgBytesPerSecmember.
- nBlockAlign
- Block alignment, in bytes. The block alignment is the minimum
atomic unit of data for the
wFormatTag
format type. If
wFormatTagis WAVE_FORMAT_PCM,
nBlockAlignshould be equal to the product of
nChannelsand
wBitsPerSampledivided by 8 (bits per byte). For non-PCM
formats, this member must be computed according to the
manufacturer's specification of the format tag.
Playback and record software must process a multiple of nBlockAlignbytes of data at a time. Data written and read from a device must always start at the beginning of a block. For example, it is illegal to start playback of PCM data in the middle of a sample (that is, on a non-block-aligned boundary).
- wBitsPerSample
- Bits per sample for the wFormatTag format type. If wFormatTagis WAVE_FORMAT_PCM, then wBitsPerSampleshould be equal to 8 or 16. For non-PCM formats, this member must be set according to the manufacturer's specification of the format tag. Note that some compression schemes cannot define a value for wBitsPerSample, so this member can be zero.
- cbSize
- Size, in bytes, of extra format information appended to the end
of the
WAVEFORMATEXstructure. This information can be used by
non-PCM formats to store extra attributes for the
wFormatTag. If no extra information is required by the
wFormatTag, this member must be set to zero. For
WAVE_FORMAT_PCM formats only, this member is ignored.
Remarks
An example of a format that uses extra information is the Microsoft Adaptive Delta Pulse Code Modulation (MS-ADPCM) format. The wFormatTagfor MS-ADPCM is WAVE_FORMAT_ADPCM. The cbSizemember is typically set to 32. The extra information stored for WAVE_FORMAT_ADPCM is coefficient pairs required for encoding and decoding the waveform-audio data.
Requirements
Runs on Versions Defined in Include Link to Windows CE OS 2.0 and later Mmsystem.h Note This API is part of the complete Windows CE OS package as provided by Microsoft. The functionality of a particular platform is determined by the original equipment manufacturer (OEM) and some devices may not support this API.