WAVEFORMATEX Fields

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.

Default = 0

In most cases, this member contains the required average data-transfer rate, in bytes per second, for the format tag. If wFormatTag is WAVE_FORMAT_PCM, nAvgBytesPerSec should be equal to the product of nSamplesPerSec and nBlockAlign. For non-PCM formats, this member must be computed according to the manufacturer's specification of the format tag. When the Windows Media Audio 9 Codec is in quality-based variable-bit-rate mode, the high-order bytes of this member are set to 0x7fffff and the low-order byte is set to a value from one through 100 which indicates the quality level.

Typical Calculation: nSamplesPerSec * nBlockAlign

Default = 176400

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 should be equal to the product of nChannels and wBitsPerSample divided 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 nBlockAlign bytes 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).

Typical Calculation: nChannels * (wBitsPerSample / 8)

Default = 4

Number of channels in the waveform-audio data. Monaural data uses one channel and stereo data uses two channels.

Default = 2

Sample rate, in samples per second (hertz), that each channel should be played or recorded. 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.

Default = 44100

Bits per sample for the wFormatTag format type. If wFormatTag is WAVE_FORMAT_PCM, then wBitsPerSample should be equal to 8, 16 or 32. For non-PCM formats, this member must be set according to the manufacturer's specification of the format tag. Some compression schemes cannot define a value for wBitsPerSample, so this member can be zero.

Default = 16

Waveform-audio format type (see WAVEFormatTag). 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 PCM data, this value should be WAVE_FORMAT_PCM.

Default = 1 (WAVE_FORMAT_PCM)