ACMDM_STREAM

ACMDM_STREAM_CONVERT

See also ACMDM_STREAM_CLOSE, ACMDM_STREAM_OPEN, ACMDM_STREAM_PREPARE, ACMDM_STREAM_RESET, ACMDM_STREAM_SIZE, ACMDM_STREAM_UNPREPARE, ACMDRVOPENDESC, ACMDRVSTREAMHEADER, ACMDRVSTREAMINSTANCE, ACMDRVSTREAMSIZE

lParam1 = (LPARAM) pacmDSI  // see below
lParam2 = (LPARAM) pacmDSH  // see below

Sent to an Audio Compression Manager (ACM) driver to request a conversion on a previously opened conversion stream. This message is usually sent to an ACM driver in response to an acmStreamConvert call.

Return MMSYSERR_NOERROR if the operation is successful or an error value otherwise. The following errors are possible:

MMSYSERR_NOMEM	Unable to allocate resources to perform the conversion request.
MMSYSERR_NOTENABLED	The driver failed to load or initialize.

lParam1

Address of the ACMDRVSTREAMINSTANCE structure for the conversion stream that the convert request is for.

lParam2

Address of the ACMDRVSTREAMHEADER structure identifying the source and destination data blocks that should be used for the conversion.

An ACM driver must support the ACMDM_STREAM_CONVERT message if it supports the ACMDM_STREAM_OPEN message.

If the specified conversion stream was opened for asynchronous conversions, the driver should queue the ACMDRVSTREAMHEADER structure and immediately return successfully. If the stream header cannot be queued for asynchronous conversions (due to resource limitations, for example), the driver should return an error code.

If the ACMDRVSTREAMHEADER for an asynchronous conversion was successfully queued, but the driver later determines that the conversion is not possible, the driver must set the cbDstLengthUsed member of the ACMDRVSTREAMHEADER to zero and perform the DriverCallback.

Note that the following parameters for the ACMDM_STREAM_CONVERT message will be validated before calling the driver:

The lParam1 parameter will contain a valid pointer to an ACMDRVSTREAMINSTANCE structure with the same information as the corresponding ACMDM_STREAM_OPEN message.
The lParam2 parameter will contain a valid pointer to an ACMDRVSTREAMHEADER structure with the proper members initialized for the conversion request. This structure will be at least the size of the base ACMDRVSTREAMHEADER structure.
The cbStruct member of the ACMDRVSTREAMHEADER structure will be set to at least the size, in bytes, of the base ACMDRVSTREAMHEADER structure.
The remaining members of the ACMDRVSTREAMHEADER structure will be within the bounds described in the documentation for the ACMDRVSTREAMHEADER structure.
The ACMDRVSTREAMHEADER structure will be properly prepared. The ACMSTREAMHEADER_STATUSF_PREPARED flag in the fdwStatus member of the ACMDRVSTREAMHEADER structure will be set.
No invalid flag combinations will be specified in the fdwConvert member.

The driver does not need to check for these conditions.

The fdwConvert member of the ACMDRVSTREAMHEADER structure will contain flags defining how the conversion should be performed on this conversion request:

ACM_STREAMCONVERTF_BLOCKALIGN	Specifies that only integral numbers of blocks should be converted. Converted data must end on block aligned boundaries. An application uses this flag for all conversions on a stream until there is not enough source data to convert to a block-aligned destination; in which case, the last conversion will be specified without this flag.
ACM_STREAMCONVERTF_END	Specifies that the conversion stream should begin returning pending instance data. For example, if a conversion stream maintains instance data, such as the tail end of an echo filter operation, this flag should tell the driver to start returning this remaining data with optional source data. Note that this flag can be specified with the ACM_STREAMCONVERTF_START flag.
ACM_STREAMCONVERTF_START	Specifies that the conversion stream should reinitialize its instance data. For example, if a conversion stream maintains instance data, such as delta or predictor information, this flag should reset the stream to starting defaults. Note that this flag can be specified with the ACM_STREAMCONVERTF_END flag.