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The open command initializes a device. All MCI devices recognize this command.

To send this command, call the mciSendString function with the lpszCommand parameter set as follows.

  TEXT("open %s %s %s"), 



Identifier of an MCI device or device driver. This can be either a device name (as given in the registry or the SYSTEM.INI file) or the filename of the device driver. If you specify the filename of the device driver, you can optionally include the .DRV extension, but you should not include the path to the file.


Flag that identifies what to initialize. The following table lists device types that recognize the open command and the flags used by each type.

Value Meaning Meaning
cdaudio alias device_alias
type device_type
digitalvideo alias device_alias
parent hwnd
style child
style overlapped
style popup
style style_type
type device_type
overlay alias device_alias
parent hwnd
style child
style overlapped
style popup
style style_type
type device_type
sequencer alias device_alias
type device_type
vcr alias device_alias
type device_type
videodisc alias device_alias
type device_type
waveaudio alias device_alias
buffer buffer_size
type device_type

The following table lists the flags that can be specified in the lpszOpenFlags parameter and their meanings.

Value Meaning
alias device_alias Specifies an alternate name for the given device. If specified, it must be used as the device_id in subsequent commands.
elementname Specifies the name of the device element (file) loaded when the device opens.
buffer buffer_size Sets the size, in seconds, of the buffer used by the waveform-audio device. The default size of the buffer is set when the waveform-audio device is installed or configured. Typically the buffer size is set to 4 seconds. With the MCIWAVE device, the minimum size is 2 seconds and the maximum size is 9 seconds.
parent hwnd Specifies the window handle of the parent window.
shareable Initializes the device or file as shareable. Subsequent attempts to open the device or file fail unless you specify "shareable" in both the original and subsequent open commands.
MCI returns an invalid device error if the device is already open and not shareable.

The MCISEQ sequencer and MCIWAVE devices do not support shared files.

style child Opens a window with a child window style.
style overlapped Opens a window with an overlapped window style.
style popup Opens a window with a pop-up window style.
style style_type Indicates a window style.
type device_type Specifies the device type of a file.


Can be "wait", "notify", or both. For more information about these flags, see The Wait, Notify, and Test Flags.

Return Values

Returns zero if successful or an error otherwise.


MCI reserves "cdaudio" for the CD audio device type, "videodisc" for the videodisc device type, "sequencer" for the MIDI sequencer device type, "AVIVideo" for the digital-video device type, and "waveaudio" for the waveform-audio device type.

As an alternative to the "type" flag, MCI can select the device based on the extension used by the file, as recorded in the registry or the [mci extension] section of the SYSTEM.INI file.

MCI can open AVI files by using a file-interface pointer or a stream-interface pointer. To open a file by using either type of interface pointer, specify an at sign (@) followed by the interface pointer in place of the file or device name for the lpszDevice parameter. For more information about the file and stream interfaces, see "AVIFile Functions and Macros ."

The following command opens the "mysound" device:

open new type waveaudio alias mysound buffer 6

With device name "new", the waveform driver prepares a new waveform resource. The command assigns the device alias "mysound" and specifies a 6-second buffer.

You can eliminate the "type" flag if you combine the device name with the filename. MCI recognizes this combination when you use the following syntax:


The exclamation point separates the device name from the filename. The exclamation point should not be delimited by white spaces.

The following example opens the RIGHT.WAV file using the "waveaudio" device:

open waveaudio!right.wav

The MCIWAVE driver requires an asynchronous waveform-audio device.


  Windows NT/2000/XP: Included in Windows NT 3.1 and later.
  Windows 95/98/Me: Included in Windows 95 and later.

See Also

MCI, MCI Command Strings

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