MMIOM_GETFORMATINFO
The MMIOM_GETFORMATINFO message is sent to a Multimedia I/O (MMIO) procedure to request format capability metadata. The I/O procedure populates an MMFORMATINFO structure with details such as its primary `FOURCC` code, supported media types, and structural operational flags. This message is distinct because it is handled at the global driver level and does not require an active file handle or an initialized open instance.
Syntax
rc = mmioSendMessage(hmmio, MMIOM_GETFORMATINFO, (LONG)pFormatInfo, lParam2);
Parameters
- ulReserved (ULONG)
- In place of the standard `pmmioinfo` parameter, this field is reserved and set to zero. An MMIOINFO runtime instance block is not required to process this request.
- usMsg (USHORT)
- The message identifier, set to `MMIOM_GETFORMATINFO`.
- lParam1 (LONG)
- A pointer to an MMFORMATINFO structure. The I/O procedure populates this structure with its registration details, format keys, and functional capabilities.
- lParam2 (LONG)
- This parameter is not used.
Return Value
- rc (ULONG)
- Return codes indicating success or failure:
- MMIO_SUCCESS: The requested format information was successfully written to the structure.
- MMIO_ERROR: The format inquiry or configuration extraction failed.
Remarks
- **Subsystem Initialization**: The MMIO Manager issues this message when loading or registering an I/O procedure into the system registry (e.g., during startup or dynamic installation). It helps the subsystem build internal format translation maps.
- **Documentation Typo Note**: The original OS/2 reference text states for `MMIO_SUCCESS` that "The specified process installed successfully". While this message is heavily utilized *during* the installation and verification phases of custom I/O procedures, the immediate programmatic function of the message is simply to request and return format metadata to the caller.