WAVEFORMATEXTENSIBLE structure

The WAVEFORMATEXTENSIBLE structure defines the format of waveform-audio data for formats having more than two channels or higher sample resolutions than allowed by WAVEFORMATEX.

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.

• Samples
  A union that contains the following members.

  • wValidBitsPerSample
    Number of bits of precision in the signal. Usually equal to WAVEFORMATEX.wBitsPerSample. However, wBitsPerSample is the container size and must be a multiple of 8, whereas wValidBitsPerSample can be any value not exceeding the container size. For example, if the format uses 20-bit samples, wBitsPerSample must be at least 24, but wValidBitsPerSample is 20.

  • 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. Set to zero.

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

• SubFormat
  A GUID that specifies the format of the audio data. The following GUIDs are defined in Ksmedia.h. Third parties can define additional GUIDs.

  Value	Meaning
  KSDATAFORMAT_SUBTYPE_ADPCM	Adaptive delta pulse code modulation (ADPCM)
  KSDATAFORMAT_SUBTYPE_ALAW	A-law coding.
  KSDATAFORMAT_SUBTYPE_DRM	DRM-encoded format for digital-audio content protected by Microsoft Digital Rights Management.
  KSDATAFORMAT_SUBTYPE_IEC61937_DOLBY_DIGITAL_PLUS	Dolby Digital Plus formatted for HDMI output.
  KSDATAFORMAT_SUBTYPE_IEC61937_DOLBY_DIGITAL	Dolby Digital Plus formatted for S/PDIF or HDMI output.
  KSDATAFORMAT_SUBTYPE_IEEE_FLOAT	IEEE floating-point audio.
  KSDATAFORMAT_SUBTYPE_MPEG	MPEG-1 audio payload.
  KSDATAFORMAT_SUBTYPE_MULAW	μ-law coding
  KSDATAFORMAT_SUBTYPE_PCM	PCM audio.

   

Remarks

The WAVEFORMATEXTENSIBLE structure can describe any format that can be described by the WAVEFORMATEX structure, but provides additional support for more than two channels, for greater precision in the number of bits per sample, and for new compression schemes.

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.

The following constants define some standard speaker configurations as bitwise ORs of the flags shown in the previous table.

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

Requirements