ACMDM_STREAM

ACMDM_STREAM_OPEN

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

lParam1 = (LPARAM) pacmDSI  // see below
lParam2 = reserved          // should be ignored

Sent to an Audio Compression Manager (ACM) driver to either open a conversion stream or query the stream for support. This message is usually sent to an ACM driver in response to an acmStreamOpen call.

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

ACMERR_NOTPOSSIBLE	The ACMDRVSTREAMINSTANCE structure defines a conversion stream request that cannot be satisfied by the driver.
MMSYSERR_NOMEM	Unable to allocate resources to create the conversion stream.
MMSYSERR_NOTENABLED	The driver failed to load or initialize.

lParam1

Address of the ACMDRVSTREAMINSTANCE structure that the caller is trying to create or query for support.

An ACM driver must support this message if it supports conversion operations. Note that the following parameters for the ACMDM_STREAM_OPEN message will be validated before calling the driver:

The lParam1 parameter will contain a valid pointer to an ACMDRVSTREAMINSTANCE structure with all members validated. All members of this structure will be within the bounds defined in the documentation for the ACMDRVSTREAMINSTANCE structure.
The cbStruct member of the ACMDRVSTREAMINSTANCE structure will be set to at least the size, in bytes, of the base ACMDRVSTREAMINSTANCE structure.
No invalid flag combinations will be specified in the fdwOpen member.
A driver will never be called to open a conversion stream for conversions for the same format tag unless the driver sets the ACMDRIVERDETAILS_SUPPORTF_CONVERTER flag in the fdwSupport member of the ACMDRIVERDETAILS structure returned by the driver during the ACMDM_DRIVER_DETAILS message.
A driver will never be called to open a conversion stream for conversions between two different format tags unless the driver sets the ACMDRIVERDETAILS_SUPPORTF_CODEC flag in the fdwSupport member of the ACMDRIVERDETAILS structure returned by the driver during the ACMDM_DRIVER_DETAILS message.
A driver will never be called to open a conversion stream with a filter unless the driver sets the ACMDRIVERDETAILS_SUPPORTF_FILTER flag in the fdwSupport member of the ACMDRIVERDETAILS structure returned by the driver during the ACMDM_DRIVER_DETAILS message.
A driver will never be called to open an asynchronous conversion stream unless the driver sets the ACMDRIVERDETAILS_SUPPORTF_ASYNC flag in the fdwSupport member of the ACMDRIVERDETAILS structure returned by the driver during the ACMDM_DRIVER_DETAILS message.

The driver does not need to check for these conditions.

If the ACM_STREAMOPENF_QUERY flag is specified in the fdwOpen member of the ACMDRVSTREAMINSTANCE structure, the driver should only return whether the conversion stream can be opened by the driver; but the conversion stream will not be opened. The driver should not allocate any instance data in conjunction with this flag.

If the ACM_STREAMOPENF_NONREALTIME flag is not specified in the fdwOpen member of the ACMDRVSTREAMINSTANCE structure, the driver should only succeed the message if the conversion can be done in real time. The definition of real time is highly dependent on your interpretation, though good judgment should be used here. If the driver's conversion is computationally expensive, the driver should not succeed a real-time conversion stream open request. An example of a real-time conversion client is the wave mapper, where data is converted as it is being played or recorded.