WAVEFORMATEXTENSIBLE Structure

The WAVEFORMATEXTENSIBLE structure defines the format of waveform-audio data for formats having more than two channels.

This structure is part of the Platform SDK and is declared in Mmreg.h. It is documented here for convenience.

Syntax

typedef struct {
  WAVEFORMATEX  Format;
  union {
    WORD  wValidBitsPerSample;
    WORD  wSamplesPerBlock;
    WORD  wReserved;
  } Samples;
  DWORD   dwChannelMask; 
  GUID    SubFormat;
} WAVEFORMATEXTENSIBLE, *PWAVEFORMATEXTENSIBLE;

Members

Format

WAVEFORMATEX structure that specifies the basic format. The wFormatTag member must be WAVE_FORMAT_EXTENSIBLE, defined in Mmreg.h. The cbSize member must be at least 22.

wValidBitsPerSample

Number of bits of precision in the signal. Usually equal to WAVEFORMATEX.wBitsPerSample.

wSamplesPerBlock

Number of samples contained in one compressed block of audio data. This value is used in buffer estimation. This value is used with compressed formats that have a fixed number of samples within each block. This value can be set to zero if a variable number of samples is contained in each block of compressed audio data. In this case, buffer estimation and position information needs to be obtained in other ways.

wReserved

Reserved for internal use by operating system. Set to zero.

dwChannelMask

Bitmask specifying the assignment of channels in the stream to speaker positions. See Remarks.

SubFormat

Subformat of the data, such as KSDATAFORMAT_SUBTYPE_PCM. The subformat information is similar to that provided by the tag in the WAVEFORMATEX structure's wFormatTag member.

Remarks

The dwChannelMask member specifies which channels are present in the multichannel stream. The least significant bit corresponds with the front left speaker, the next least significant bit corresponds to the front right speaker, and so on. The bits, in order of significance, are defined in Ksmedia.h and Mmreg.h as follows:

For more information on this structure, see the document Multiple Channel Audio Data and WAVE Files, available at www.microsoft.com.