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WAVEFORMATEX structure

The WAVEFORMATEX 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.

Syntax


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 Mmreg.h header file. For one- or two-channel Pulse Code Modulation (PCM) data, this value should be WAVE_FORMAT_PCM.

  • If wFormatTag equals WAVE_FORMAT_EXTENSIBLE, the structure is interpreted as a WAVEFORMATEXTENSIBLE structure.
  • If wFormatTag equals WAVE_FORMAT_MPEG, the structure is interpreted as an MPEG1WAVEFORMAT structure.
  • If wFormatTag equals WAVE_FORMAT_MPEGLAYER3, the structure is interpreted as an MPEGLAYER3WAVEFORMAT structure.

Before reinterpreting a WAVEFORMATEX structure as one of these extended structures, verify that the actual structure size is sufficiently large and that the cbSize member indicates a valid size.

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). If wFormatTag is WAVE_FORMAT_PCM, then common values for nSamplesPerSec are 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 wFormatTag is WAVE_FORMAT_PCM, nAvgBytesPerSec must equal nSamplesPerSec × nBlockAlign. For non-PCM formats, this member must be computed according to the manufacturer's specification of the format tag.

nBlockAlign

Block alignment, in bytes. The block alignment is the minimum atomic unit of data for the wFormatTag format type. If wFormatTag is WAVE_FORMAT_PCM, nBlockAlign must equal (nChannels × wBitsPerSample) / 8. For non-PCM formats, this member must be computed according to the manufacturer's specification of the format tag.

Software must process a multiple of nBlockAlign bytes of data at a time. Data written to 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 wFormatTag is WAVE_FORMAT_PCM, then wBitsPerSample should 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. If wFormatTag is WAVE_FORMAT_EXTENSIBLE, this value can be any integer multiple of 8.

Some compression schemes do not 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 WAVEFORMATEX structure. 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 (and only WAVE_FORMAT_PCM formats), this member is ignored. However it is still recommended to set the value.

Requirements

Header

Mmreg.h

See also

DirectShow Structures
WAVEFORMATEXTENSIBLE Structure

 

 

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