ACMDRVSTREAMHEADER (Compact 2013)

3/26/2014

This structure describes a source buffer and a destination buffer associated with a conversion stream. This structure is used with the ACMDM_STREAM_PREPARE, ACMDM_STREAM_UNPREPARE, and ACMDM_STREAM_CONVERT messages.

Syntax

typedef struct {
  DWORD cbStruct; 
  DWORD fdwStatus; 
  DWORD dwUser; 
  LPBYTE pbSrc; 
  DWORD cbSrcLength; 
  DWORD cbSrcLengthUsed;
  DWORD dwSrcUser; 
  LPBYTE pbDst; 
  DWORD cbDstLength; 
  DWORD cbDstLengthUsed; 
  DWORD dwDstUser; 
  DWORD fdwConvert; 
  LPACMDRVSTREAMHEADER padshNext; 
  DWORD fdwDriver; 
  DWORD dwDriver; 
  DWORD fdwPrepared; 
  DWORD dwPrepared; 
  LPBYTE pbPreparedSrc; 
  DWORD cbPreparedSrcLength; 
  LPBYTE pbPreparedDst; 
  DWORD cbPreparedDstLength; 
} ACMDRVSTREAMHEADER;

Members

• cbStruct
  Value that specifies the size, in bytes, of the structure.

• fdwStatus
  Value that contains status flags. The following table shows the possible values for fdwStatus.

  Value	Description
  ACMSTREAMHEADER_STATUSF_DONE	Value that indicates that a conversion is complete. For synchronous conversion, the ACM sets this flag when the driver returns from an ACMDM_STREAM_CONVERT message. For asynchronous drivers, the driver sets this flag after the data has been converted. The ACM clears the flag before sending each ACMDM_STREAM_CONVERT message.
  ACMSTREAMHEADER_STATUSF_PREPARED	Value that indicates that the data buffers have been prepared. This flag is set by the ACM, regardless of whether the driver or the ACM prepared the buffers. See ACMDM_STREAM_PREPARE and ACMDM_STREAM_UNPREPARE.
  ACMSTREAMHEADER_STATUSF_INQUEUE	Value that is used by the driver during asynchronous conversions to indicate that the structure has been queued for conversion. The driver is responsible for setting and clearing this flag. See ACMDM_STREAM_CONVERT.

• dwUser
  Value that specifies information supplied by a client for its own use.

• pbSrc
  Pointer to a source buffer. For an ACMDM_STREAM_CONVERT message, this buffer contains the data to be converted.

• cbSrcLength
  Value that specifies the length, in bytes, of the source buffer pointed to by pbSrc. For the ACMDM_STREAM_PREPARE and ACMDM_STREAM_UNPREPARE messages, this value represents the maximum source buffer size. For ACMDM_STREAM_CONVERT, this value represents the length of the data in the buffer.

• cbSrcLengthUsed
  Value that specifies the length, in bytes, of source data that has been converted. The driver sets this value to indicate the number of bytes in the source buffer that the driver actually converted. The value cannot be greater than the value in cbSrcLength.

• dwSrcUser
  Value that specifies information supplied by a client for its own use.

• pbDst
  Pointer to a destination buffer. For an ACMDM_STREAM_CONVERT message, the driver fills this buffer with converted data.

• cbDstLength
  Value that specifies the length, in bytes, of the destination buffer pointed to by pbDst.

• cbDstLengthUsed
  Value that specifies the length, in bytes, of destination data that has been converted. The driver sets this value to indicate the number of converted bytes that it has placed in the destination buffer. The value cannot be greater than the value in cbDstLength. If the conversion fails, the driver must set this value to 0.

• dwDstUser
  Value that specifies information supplied by a client for its own use.

• fdwConvert
  Value that specifies the acmStreamConvert function's fdwConvert parameter. The following table shows the possible values for fdwConvert.

  Value	Description
  ACMDM_STREAM_PREPARE	Not used.
  ACMDM_STREAM_UNPREPARE	Not used.
  ACMDM_STREAM_CONVERT	Value that specifies the acmStreamConvert function's fdwConvert parameter.

  The following table shows the possible values for the ACMDM_STREAM_CONVERT value.

  Value	Description
  ACM_STREAMCONVERTF_BLOCKALIGN	Value that indicates that only whole blocks of source data should be converted. The size of a block is obtained from the source format's WAVEFORMATEX structure. See ACMDRVSTREAMINSTANCE. If this flag is set, the driver should not convert extra bytes that do not make up a whole block. Generally, clients set this flag for all buffers in a conversion stream except the last one.
  ACM_STREAMCONVERTF_START	Value that indicates that the driver re-initializes stream instance data, such as predictor coefficients or scale factors, to default starting values. This flag can be specified with the ACM_STREAMCONVERTF_END flag.
  ACM_STREAMCONVERTF_END	Value that indicates that the driver returns end-of-stream data, such as tail end echo data for an echo filter, in the destination buffer along with data converted from the source buffer. This flag can be specified with the ACM_STREAMCONVERTF_START flag.

• padshNext
  Pointer to another ACMDRVSTREAMHEADER structure. An asynchronous driver can use this member for creating a queue of pending conversion requests. The ACM clears this member prior to sending an ACMDM_STREAM_PREPARE or ACMDM_STREAM_CONVERT message.

• fdwDriver
  Value that contains stream instance information supplied by the driver for its own use. This member is intended for storing driver-defined flags, but you can use it for storing any data that fits into a DWORD. The ACM clears this member prior to sending an ACMDM_STREAM_PREPARE message. Otherwise, its value is preserved from one message to the next.

• dwDriver
  Value that specifies stream instance information supplied by the driver for its own use. You can use this member for any purpose. The ACM clears this member prior to sending an ACMDM_STREAM_PREPARE message. Otherwise, its value is preserved from one message to the next.

• fdwPrepared
  Value that specifies the fdwPrepared member of the acmStreamPrepare

  Header function. Used by the ACM only.

• dwPrepared
  Value that specifies the parameter of acmStreamPrepare

  Header. Used by the ACM only.

• pbPreparedSrc
  Pointer to the source buffer supplied with acmStreamPrepare

  Header. Used by the ACM only.

• cbPreparedSrcLength
  Specifies the length of the source buffer supplied with acmStreamPrepare

  Header. Used by the ACM only.

• pbPreparedDst
  Pointer to the destination buffer supplied with acmStreamPrepare

  Header. Used by the ACM only.

• cbPreparedDstLength
  Value that specifies the length of the destination buffer supplied with the acmStreamPrepare

  Header function. Used by the ACM only.

Requirements

See Also

Reference

ACM Driver Structures

Other Resources

WAVEFORMATEX (Waveform Audio)