How To Play an AVI File w/ an API Call to 16-bit Mmsystem.dll

 Last reviewed: October 18, 1996
Article ID: Q136763
The information in this article applies to:
  • Microsoft Visual FoxPro for Windows, versions 3.0, 5.0

SUMMARY

There are several ways to play AVI (audio-visual interleave) files from Visual FoxPro. These include:

  • Placing the AVI file in a General field and then activating it.
  • Using a Custom control designed to play MCI (media control interface) devices.
  • Calling a Windows API function directly that will play the file for you.

The last technique, although more involved, gives the developer much more control over how the AVI file will appear during playback. This article explains how to play an AVI file using API functions contained in the Windows 16-bit Mmsystem.dll file.

MORE INFORMATION

The API function MCIEXECUTE can be used to access a variety of MCI devices including those required to play AVI files. MCIEXECUTE is located in the Windows file MMSYSTEM.DLL (typically located in the Windows System directory). Since MMSYSTEM is a 16 bit Dynamic Link Library, you must use the REGFN and CALLFN statements in FOXTOOLS.FLL to register this function (the DECLARE statement in Visual FoxPro can only be used with 32 bit DLL's).

Once the MCIEXECUTE function has been registered, you can use it to send a variety of MCI commands to open, play and close an AVI file. The syntax of the MCI command string allows you to control many attributes of the AVI playback window such as it's size, position, speed and direction (forward or reverse).

The following procedure describes how to create a Form that can be used to play an AVI file.

  1. Open or switch to Visual FoxPro and open a new Form.

  2. Place the following code in the INIT event of the form: 

         PUBLIC MCIEXE
     SET LIBRARY TO FOXTOOLS.FLL
     MCIEXE = REGFN("MCIExecute" ,"C","I", "MMSYSTEM.DLL") && Registers ;
     the MCIEXECUTE API function using FOXTOOLS.FLL

  3. Create a Command Button on the Form and place the following code in the click event of the button (you can make the Caption of the Button read something like "Play AVI File"): 

         cAVIFile = SYS(2004) + "TEST.AVI" && Specifies the path to, and ;
     the name of the AVI file to be played
     nRESULT = CALLFN(MCIEXE, "open " + cAVIFile + " TYPE AVIVIDEO alias ;
     wind style popup") && Opens an instance of the MCI device type;
     AVIVIDEO and gives it the alias name 'wind'
     nRESULT = CALLFN(MCIEXE, "play wind wait") && Plays the AVI file ;
     suspending further MCI command strings until this one is complete
     nRESULT = CALLFN(MCIEXE,"close wind") && Closes the instance of the ;
     MCI device driver specified by the alias 'wind'

NOTE: The above code assumes that the AVI file to be played is called TEST.AVI and is located in the Visual FoxPro directory. You should modify this line appropriately so that the variable AVIFILE will contain a string that contains the complete path and file name of the AVI file to be played. If the MCIEXECUTE is executed successfully, nRESULT will be 1.

  1. Save and run the Form. Note that the AVI file will play when you click the Command Button created in step 3 above.

Now that you have successfully played an AVI file from Visual FoxPro, there 
 are a number of things you can do to control how the playback window
appears. For example adding the line: 

     nRESULT = CALLFN(MCIEXE, "put wind window at 300 200 164 147")
just prior to the line: 

     nRESULT = CALLFN(MCIEXE, "play wind wait")
in the click event of the Command Button allows you to control where the playback window will appear, and what it's dimensions will be. In this example the upper left hand corner of the window will be at pixel position 300, 200 (where the upper left hand corner of the screen is the origin of 0,0) and will have a width of 164 pixels and a height of 147 pixels.

Another example that demonstrates modifying the play back window is: 

     nRESULT = CALLFN(MCIEXE, "SET WIND SPEED 500")
Adding this line immediately prior to the line: 

     nRESULT = CALLFN(MCIEXE, "play wind wait")
in the click event of the Command Button allows you to control the speed at which the AVI file will play. In this example it will play a one half of its original speed (1 second to 500 milliseconds).

You can also control the direction in which the AVI file will play. Replace the code in the Click event of the Command Button with the following to demonstrate this ability: 

     cAVIFile = SYS(2004) + "TEST.AVI" && Specifies the path to, and ;
     the name of the AVI file to be played
     nRESULT = CALLFN(MCIEXE, "open " + cAVIFile + " TYPE AVIVIDEO alias ;
     wind style popup") && Opens an instance of the MCI device type;
     AVIVIDEO and gives it the alias name 'wind'
     nRESULT = CALLFN(MCIEXE, "SET wind TIME FORMAT MILLISECONDS") && Sets;
     the playback format to milliseconds (as opposed to frames)
     nRESULT = CALLFN(MCIEXE, "PLAY wind WINDOW FROM 5000 TO 0 WAIT") ;
     && Note that the above line specifies to play the AVI file from time ;
     position 5000 (milliseconds) to time position 0 (Beginning of the ;
     file). If your AVI file is less than 5000 milliseconds in length, ;
     adjust this line accordingly
     nRESULT = CALLFN(MCIEXE,"close wind") && Closes the instance of the ;
     MCI device driver specified by the alias 'wind'
There are many other things you can do to control the playback of AVI files using MCI Command Strings. For more information on these see Appendix F of the Microsoft Video for Windows User's Guide.

Additional reference words: 5.00 3.00
KBCategory: kbprg
KBSubcategory: FxprgFoxtools

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Last reviewed: October 18, 1996
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