MPEGLAYER3WAVEFORMAT structure (mmreg.h)

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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 Meaning
MPEGLAYER3_FLAG_PADDING_ISO
0x00000000
 Insert padding as needed to achieve the stated average bitrate.
MPEGLAYER3_FLAG_PADDING_ON
0x00000001
 Always insert padding. The average bit rate may be higher than stated.
MPEGLAYER3_FLAG_PADDING_OFF
0x00000002
 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.

Requirements

Requirement Value
Header mmreg.h

See also

DirectShow Structures