MCI_PLAY

The `MCI_PLAY` message initiates playback for a media device. It allows for specifying start and end positions, as well as device-specific playback modes like fast-forward, reverse, or scan.

Syntax

param1
ULONG ulParam1; /* Playback flags. */

param2
PMCI_PLAY_PARMS pParam2; /* Pointer to a play parameter structure. */

Parameters

ulParam1 (ULONG) - input

The following general flags apply to all devices:

• MCI_NOTIFY Posts a notification message when the action completes.
• MCI_WAIT Does not return control until playback reaches the "To" position or is stopped.
• MCI_FROM Uses the ulFrom field in pParam2 as the start position. Defaults to current position if not set.
• MCI_TO Uses the ulTo field in pParam2 as the end position. Defaults to the end of media if not set.

Digital Video Extensions

Additional flags for digital video:

• MCI_DGV_PLAY_SPEED Uses the ulSpeed field for playback rate.
• MCI_DGV_PLAY_REVERSE Plays the video in reverse.
• MCI_DGV_PLAY_FAST Plays at twice the normal rate.
• MCI_DGV_PLAY_SLOW Plays at half the normal rate.
• MCI_DGV_PLAY_SCAN Plays as quickly as possible with audio disabled.

Videodisc Extensions

Additional flags for videodiscs (Reverse and Scan are mutually exclusive):

• MCI_VD_PLAY_REVERSE, MCI_VD_PLAY_FAST, MCI_VD_PLAY_SCAN, MCI_VD_PLAY_SPEED, MCI_VD_PLAY_SLOW.

pParam2 (PMCI_PLAY_PARMS) - input

Points to an MCI_PLAY_PARMS structure. For extended devices, this may point to MCI_DGV_PLAY_PARMS or MCI_VD_PLAY_PARMS.

Returns

rc (ULONG) - returns

* MCIERR_SUCCESS Playback started successfully.

• MCIERR_DEVICE_NOT_READY The device is busy or has no media.
• MCIERR_OUTOFRANGE The "From" or "To" positions are invalid.
• MCIERR_CHANNEL_OFF The primary audio/video channel is disabled.

Remarks

Positions provided in `ulFrom` and `ulTo` must match the currently set time format (e.g., milliseconds, frames, or MMTIME).

When playback reaches the `ulTo` position:

• The current position of the media is updated to the `ulTo` value.
• If a file has 100 samples (0–99) and you play from 10 to 80, samples 10 through 79 are played. The final position will be 80.

> [!IMPORTANT] > **Digital Video Deadlock:** If your application uses the `MCI_WAIT` flag on the main GUI thread without direct-access drivers, the application may hang. Always use a separate thread for `MCI_WAIT` operations or use `MCI_NOTIFY`.

Example Code

The following code initiates playback from the 5-second mark to the 25-second mark, assuming the time format is set to milliseconds.

   USHORT          usDeviceID;
   MCI_PLAY_PARMS  mpp;

   /* Setup callback for notification when 25s is reached */
   mpp.hwndCallback = (HWND) hwndMyWindow;

   /* Set positions in milliseconds */
   mpp.ulFrom = (ULONG) 5000;  
   mpp.ulTo   = (ULONG) 25000; 

   mciSendCommand(usDeviceID,
                  MCI_PLAY,
                  MCI_NOTIFY | MCI_FROM | MCI_TO,
                  (PVOID) &mpp,
                  0);

Related Messages

• MCI_SET (to change time format)
• MCI_STOP
• MCI_PAUSE
• MCI_RESUME