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.

Value Meaning
at position Specifies the frame to invoke a signal.
cancel Removes 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 interval Specifies 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 position Indicates 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 id Specifies 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 Values

Returns zero if successful or an error otherwise.


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


**  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, MM_MCISIGNAL