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MPEGLAYER3WAVEFORMAT Structure

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Microsoft DirectShow 9.0

MPEGLAYER3WAVEFORMAT Structure

The MPEGLAYER3WAVEFORMAT structure describes an MPEG Audio Layer-3 (MP3) audio format.

Syntax

typedef struct mpeglayer3waveformat_tag {
  WAVEFORMATEX  wfx;
  WORD          wID;
  DWORD         fdwFlags;
  WORD          nBlockSize;
  WORD          nFramesPerBlock;
  WORD          nCodecDelay;
} MPEGLAYER3WAVEFORMAT;

Members

wfx

WAVEFORMATEX structure that specifies the basic audio format. The wFormatTag member must be WAVE_FORMAT_MPEGLAYER3. The cbSize member must be at least 12. (For cbSize, you can use the constant MPEGLAYER3_WFX_EXTRA_BYTES, defined in the Mmreg.h.)

wID

Set this structure member to MPEGLAYER3_ID_MPEG.

fdwFlags

Indicates whether padding is used to adjust the average bitrate to the sampling rate. Use one of the following values:

Value Description
MPEGLAYER3_FLAG_PADDING_ISO Insert padding as needed to achieve the stated average bitrate.
MPEGLAYER3_FLAG_PADDING_ON Always insert padding. The average bit rate may be higher than stated.
MPEGLAYER3_FLAG_PADDING_OFF Never insert padding. The average bit rate may be lower than stated.

nBlockSize

Block size in bytes. This value equals the frame length in bytes x nFramesPerBlock. For MP3 audio, the frame length is calculated as follows: 144 x (bitrate / sample rate) + padding.

nFramesPerBlock

Number of audio frames per block.

nCodecDelay

Encoder delay in samples. If you do not know this value, set this structure member to zero.

Remarks

If you are using an audio compression manager (ACM) codec, you can use the acmFormatEnum function to fill in this structure.

Requirements

Header: mmreg.h.

See Also