View source for MMIO Functions - MMIO Messages

The MMIO messages are sent to an I/O procedure as a result of an MMIO function call. For example, when an application calls [[mmioOpen]], the [[MMIOM_OPEN]] message is sent to an I/O procedure. An application can also send the MMIO messages to an I/O procedure by issuing [[mmioSendMessage]] or by directly calling the I/O procedure.

The [[mmioSendMessage]] function should be used only to pass user-defined messages, or messages not automatically generated by an MMIO function, to the I/O procedure of the user's application.

When an application issues [[mmioSendMessage]], it passes an hmmio parameter, which MMIO converts to an MMIOINFO block before sending the parameter to the I/O procedure. When an application calls an I/O procedure directly, a pmmioinfo parameter is passed to the I/O procedure instead of an hmmio. The following is a function prototype for a direct I/O procedure call:

 LONG APIENTRY MMIOPROC (PVOID pmmioinfo, USHORT usMsg, LONG lParam1, LONG lParam2);

{| class="wikitable sortable"
! Message
! Description
|-
| MMIOM_BEGININSERT || Requests that all subsequent Writes insert data at the current seek position.
|-
| MMIOM_BEGINRECORD || Requests all subsequent Writes be considered one logical unit by an UNDO or REDO.
|-
| MMIOM_BEGINSTREAM || Sent before the first mmioRead or mmioWrite to start the stream at the optimum rate for the file.
|-
| MMIOM_CLEAR || Requests that a specified range be deleted from a file.
|-
| MMIOM_CLOSE || Requests that the file be closed.
|-
| MMIOM_COPY || Requests that a specified range be copied to the clipboard.
|-
| MMIOM_CUT || Requests that a specified range be copied to the clipboard and then deleted.
|-
| MMIOM_ENDSTREAM || Sent after the last mmioRead or mmioWrite to end the stream.
|-
| MMIOM_DELETE || Requests that information be removed from a file.
|-
| MMIOM_ENDINSERT || Requests that all subsequent Writes overwrite data at the current seek position.
|-
| MMIOM_ENDRECORD || Indicates that the logical record operation has ended and data structures should be updated, if necessary.
|-
| MMIOM_GETCF || Obtains the handle (hmmcf) of the RIFF compound file.
|-
| MMIOM_GETCFENTRY || Requests a CTOC entry for an element of a RIFF compound file.
|-
| MMIOM_GETFORMATINFO || Requests that the IOProc return an MMFORMATINFO structure.
|-
| MMIOM_GETFORMATNAME || Requests the format name for the IOProc.
|-
| MMIOM_GETHEADER || Requests that the IOProc return media-specific information.
|-
| MMIOM_IDENTIFYFILE || Attempts to determine if any IOProc can process a file.
|-
| MMIOM_MULTITRACKREAD || Requests that data be read from a movie file.
|-
| MMIOM_MULTITRACKWRITE || Requests that data be written to a movie file.
|-
| MMIOM_OPEN || Requests that a file be opened or deleted.
|-
| MMIOM_PASTE || Requests that data from the clipboard be inserted into a file.
|-
| MMIOM_QUERYHEADERLENGTH || Requests that the IOProc return the size the header.
|-
| MMIOM_QUERYIMAGE || Requests that the IOProc return the currently selected image index in the image file.
|-
| MMIOM_QUERYIMAGECOUNT || Requests that the IOProc return the number of images stored in the image file.
|-
| MMIOM_READ || Requests that bytes be read from an open file.
|-
| MMIOM_REDO || Requests that the last logical action which was undone be redone.
|-
| MMIOM_SAVE || Requests temporary changes in a file.
|-
| MMIOM_SEEK || Requests that the current file position be moved.
|-
| MMIOM_SEEKBYTIME || Requests that the file position be moved relative to some unit of time.
|-
| MMIOM_SET || Requests that extended file information be set or queried.
|-
| MMIOM_SETHEADER || Requests that the IOProc use media-specific information when writing or accepting data.
|-
| MMIOM_SETIMAGE || Selects a new image index in the image file.
|-
| MMIOM_STATUS || Used to pass appropriate MCI_STATUS requests to an IOProc.
|-
| MMIOM_TEMPCHANGE || Requests that all subsequent Writes to the media be treated as temporary changes.
|-
| MMIOM_UNDO || Requests that the last logical action, either a delete, insert, undo, or redo, be undone.
|-
| MMIOM_WINMSG || Allows an application or an MCD to pass PM messages from a window procedure to an IOProc.
|-
| MMIOM_WRITE || Requests that the bytes be written to an open file.
|}

The MMIO messages indicate, to the I/O procedure, the type of MMIO operation to be performed. I/O procedures can be called to process files that might or might not use the RIFF format standard.

;Note: The compound-file messages must not be used while creating or appending to the compound file itself.