The topic you requested is included in another documentation set. For convenience, it's displayed below. Choose Switch to see the topic in its original location.

signal command

The signal command identifies a specified position in the workspace by sending the application an MM_MCISIGNAL message. Digital-video devices recognize this command. MCIAVI supports only one active signal at a time.

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

  TEXT("signal %s %s %s"), 



Identifier of an MCI device. This identifier or alias is assigned when the device is opened.


One of the following flags.

at positionSpecifies the frame to invoke a signal.
cancelRemoves signals from the workspace. An individual signal is specified by using the "uservalue" flag. If the "uservalue" flag is not specified by using "cancel", the device cancels all signals. The "cancel" flag is incompatible with the "at", "every", and "return position" flags.
every intervalSpecifies the period of the signals. The interval value is specified in the current time format.

If used with "at" position, signals are placed throughout the workspace with one signal mark placed at position.

Without the "at" flag, signals are placed throughout the workspace with one signal at the current position.

If this flag is omitted, only the position indicated by the "at" flag is marked.

If the interval value is less than the minimum frequency supported by a device, it will use its minimum value.

return positionIndicates the device should send the position value instead of the "uservalue" identifier in the signaling message. The "uservalue" identifier can still be used to cancel or to redefine the signal marks.
uservalue idSpecifies an identifier that is reported back with the signaling message. This identifier acts as an identifier that can be used with other signal commands to reference this signal setting. If omitted, the default value is zero.



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

Return Value

Returns zero if successful or an error otherwise.


The window handle used for notification of command completion messages is also used for signaling.


Minimum supported client

Windows 2000 Professional [desktop apps only]

Minimum supported server

Windows 2000 Server [desktop apps only]

See also

MCI Command Strings