Classifications of MCI Commands - Win32 Multimedia Programmer's Reference

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Classifications of MCI Commands

MCI defines four command classifications: system, required, basic, and extended. The following list describes these command classifications:

System commands are handled by MCI directly, rather than by the driver.
Required commands are handled by the driver. All MCI drivers must support the required commands and flags.
Basic commands (or optional commands) are used by some devices. If a device supports a basic command, it must support a defined set of flags for that command.
Extended commands are specific to a device type or driver. Extended commands include commands, like the put (MCI_PUT) and where (MCI_WHERE) commands for the digitalvideo and overlay device types, and extensions to existing commands (like the "stretch" flag of the status (MCI_STATUS) command for the overlay device type).

While system and required commands are the minimum command set for any MCI driver, basic and extended commands are not supported by all drivers. Your application can always use system and required commands and their flags, but if it needs to use a basic or extended command or flag, it should first query the driver by using the capability (MCI_GETDEVCAPS) command. The following sections summarize the specific commands in each category.

System Commands
MCI processes the following system commands directly, rather than passing them to MCI devices.

String	Message	Description
break	MCI_BREAK	Sets a break key for an MCI device.
sysinfo	MCI_SYSINFO	Returns information about MCI devices.

Required Commands
All MCI devices support the following required commands.

String	Message	Description
capability	MCI_GETDEVCAPS	Obtains the capabilities of a device.
close	MCI_CLOSE	Closes the device.
info	MCI_INFO	Obtains textual information from a device.
open	MCI_OPEN	Initializes the device.
status	MCI_STATUS	Obtains status information from the device. Some of this command's flags are not required, so it is also a basic command.

Devices must also support a standard set of command flags for the required commands.

Basic Commands
The following list summarizes the basic commands. The use of these commands by an MCI device is optional.

String	Message	Description
load	MCI_LOAD	Loads data from a file.
pause	MCI_PAUSE	Stops playing. Playback or recording can be resumed at the current position.
play	MCI_PLAY	Starts transmitting output data.
record	MCI_RECORD	Starts recording input data.
resume	MCI_RESUME	Resumes playing or recording on a paused device.
save	MCI_SAVE	Saves data to a disk file.
seek	MCI_SEEK	Seeks forward or backward.
set	MCI_SET	Sets the operating state of the device.
status	MCI_STATUS	Obtains status information about the device. This is also a required command; since some of its flags are not required, it is also listed here. (The optional items support devices that use linear media with identifiable positions.)
stop	MCI_STOP	Stops playing.

If a driver supports a basic command, it must also support a standard set of flags for the command.

Extended Commands
Some MCI devices have additional commands, or they add flags to existing commands. While some extended commands apply only to a specific device driver, most of them apply to all drivers of a particular device type. For example, the command set for the sequencer device type extends the set (MCI_SET) command to add time formats that are needed by MIDI sequencers.

You should not assume that the device supports the extended commands or flags. You can use the capability (MCI_GETDEVCAPS) command to determine whether a specific feature is supported, and your application should be ready to deal with "unsupported command" or "unsupported function" return values.

The following extended commands are available with the listed device types.

String	Message	Device types	Description
configure	MCI_CONFIGURE	digitalvideo	Displays a configuration dialog box.
cue	MCI_CUE	digitalvideo, waveaudio	Prepares for playing or recording.
delete	MCI_DELETE	waveaudio	Deletes a data segment from the media file.
escape	MCI_ESCAPE	ideodisc	Sends custom information to a device.
freeze	MCI_FREEZE	overlay	Disables video acquisition to the frame buffer.
put	MCI_PUT	digitalvideo, overlay	Defines the source, destination, and frame windows.
realize	MCI_REALIZE	digitalvideo	Tells the device to select and realize its palette into a device context of the displayed window.
setaudio	MCI_SETAUDIO	digitalvideo	Sets audio parameters for video.
setvideo	MCI_SETVIDEO	digitalvideo	Sets video parameters.
signal	MCI_SIGNAL	digitalvideo	Identifies a specified position with a signal.
spin	MCI_SPIN	ideodisc	Starts the disc spinning or stops the disc from spinning.
step	MCI_STEP	digitalvideo, videodisc	Steps the play one or more frames forward or reverse.
unfreeze	MCI_UNFREEZE	overlay	Enables the frame buffer to acquire video data.
update	MCI_UPDATE	digitalvideo	Repaints the current frame into the device context.
where	MCI_WHERE	digitalvideo, overlay	Obtains the rectangle specifying the source, destination, or frame area.
window	MCI_WINDOW	digitalvideo, overlay	Controls the display window.

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