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Posted 19 Oct 2005


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Fun with C# and the Flash Player 8 External API

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4.72/5 (31 votes)
19 Oct 20054 min read
Demonstrates how to communicate between Flash Player 8 and C# using the new External API


After hearing of all the great new enhancements made to Flash Player 8 during Macromedia MAX this year, I was inspired to take one of the new features that caught my eye for a test drive. The feature I am speaking of is the External API.

The External API allows an ActionScript developer to easily interact with the container program that is hosting Flash Player 8 and vice versa. The majority of the time, this will most likely be a Web browser, but this does not always have to be the case.

As many C# developers know, it is easy to house an ActiveX control (the IE version of Flash Player 8) in a .NET Windows application. This means we can now load an SWF in our Windows application and easily send data back and forth. Keep in mind that the keyword in this statement is "easily;" although possible before, it was not nearly as simple as the External API makes it now!

For my test application, I decided to begin porting over the FLVPlayer I built earlier this year using Flash Player 7, to Flash Player 8. This is just a simple program that allows double click playback of FLV encoded video.

C# -> ActionScript Communication

As I said before, communication between Flash Player 8 and its container has been made extremely easy. The new class that makes this process so easy is the ExternalInterface. We will begin in the ActionScript. First, we need to import this new class so we can use it:

import flash.external.ExternalInterface;

Next, we have to register any function we want to make available externally:

ExternalInterface.addCallback("loadAndPlayVideo", null, loadAndPlayVideo);

Basically, the code above will allow us to call the loadAndPlayVideo function (which I will show in a minute) from the C# application. The second argument is null because the loadAndPlayVideo function is declared on the _root of the timeline.

The loadAndPlayVideo function is as below. Basically, it takes a file path and sets it as the content path in an instance of the FLVPlayback component named videoPlayer.

function loadAndPlayVideo(uri:String):Void
    videoPlayer.contentPath = uri;

That's it from the ActionScript side. Now all we need to do is call the function from C#. First, I add an instance of the Flash Player 8 ActiveX control to my form and load the SWF we created in the form's constructor:

private AxShockwaveFlash flashPlayer;

public FLVPlayer ()
     // Error handling removed for the sake of condensing the code
     flashPlayer.LoadMovie(0, Application.StartupPath + "\\player.swf");

Next, all we have to do is call the externalized method when desired. In my case, it is in response to the user selecting a file from a standard OpenFileDialog:

fileDialog = new OpenFileDialog();
fileDialog.Filter = "*.flv|*.flv";
fileDialog.Title = "Select a Flash Video file...";
fileDialog.Multiselect = false;
fileDialog.RestoreDirectory = true;

if(fileDialog.ShowDialog() == DialogResult.OK)
     flashPlayer.CallFunction("<invoke" + 
          " name=\"loadAndPlayVideo\" returntype=\"xml\">
          <arguments><string>" + fileDialog.FileName + 

That's it! As you can see, we call loadAndPlayVideo by sending in a specially formatted XML string containing the name of the method to invoke and the list of function parameters.

ActionScript -> C# Communication

Again, you will need to include the ExternalInterface in the ActionScript:

import flash.external.ExternalInterface;

Then to make the call from ActionScript we use a static method on the ExternalInterface class:

      videoPlayer.metadata.width, videoPlayer.metadata.height);

As you can see, I am calling a method called ResizePlayer and passing the width and height of the video currently loaded as parameters. Now to receive the message in C#, we first have to subscribe to the FlashCall event. To do this, I added the following line to the form's constructor:

flashPlayer.FlashCall += 
  new _IShockwaveFlashEvents_FlashCallEventHandler(flashPlayer_FlashCall);

Now the call made in ActionScript will be received in the request property of the event argument. For my particular call, the XML will look like this:

<invoke name="ResizePlayer" returntype="xml">

So now all we have to do is parse the XML in the event handler and invoke the C# function locally:

XmlDocument document = new XmlDocument();

// Get all the arguments
XmlNodeList list = document.GetElementsByTagName("arguments");

// Since in this case I only have one call from ActionScript to C# I
// know I need to invoke the ResizePlayer function

Viola! It is now that easy to pass data back and forth between ActionScript and C#.

What's Next?

As I am sure many of you are thinking, writing and parsing of the XML being sent back and forth can be completely plucked out and wrapped up into utility classes for easy re-use.

As time permits, I will continue to work on porting FLVPlayer into the Flash Player 8 era and will work on building the utility classes necessary. Look for another article with details, when completed…

Example Code

Sample Image - flashexternalapi.jpg

I have made the simple example discussed available. Keep in mind this is only meant to demonstrate the External API and is not the final version of the FLVPlayer. In fact, if you try to load a video larger then 320x240, you will see that the resize functionality is not complete.


This article has no explicit license attached to it but may contain usage terms in the article text or the download files themselves. If in doubt please contact the author via the discussion board below.

A list of licenses authors might use can be found here


About the Author

Gabe Wishnie
Web Developer
United States United States
.NET Software Developer

- Working towards M.S. Computer Science
- B.S. Computer Science
- B.S. Computer Information Systems
- Minor Mathematics

- Microsoft Certified Application Developer
- Microsoft Certified Professional
- C# ASP.NET Developer (4 years)

Other Interests
- Flash Remoting
- Video Encoding (Windows Media and Flash Video)
- Microsoft Content Management Server

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Comments and Discussions

GeneralMy vote of 4 Pin
mutterholzbein20-Nov-12 6:42
Membermutterholzbein20-Nov-12 6:42 
GeneralMy vote of 4 Pin
Burak Tunçbilek9-Jul-12 12:02
MemberBurak Tunçbilek9-Jul-12 12:02 
GeneralMy vote of 2 Pin
mannu9t31-Jan-12 5:49
Membermannu9t31-Jan-12 5:49 
QuestionSending large data to flash Pin
vhad0125-Aug-11 21:15
Membervhad0125-Aug-11 21:15 
GeneralMy vote of 5 Pin
mahtab_y_n20-Jun-11 21:49
Membermahtab_y_n20-Jun-11 21:49 
QuestionHow can I know in my C# application when the FLV Video reach the end !!! Pin
Soit Mircea Ioan8-Apr-11 2:16
MemberSoit Mircea Ioan8-Apr-11 2:16 
AnswerRe: How can I know in my C# application when the FLV Video reach the end !!! Pin
Member 460580225-Aug-12 5:15
MemberMember 460580225-Aug-12 5:15 
GeneralProblems receiving Events Pin
fridolin Mueller1-Mar-11 10:52
Memberfridolin Mueller1-Mar-11 10:52 
QuestionDo you have a new .swf file to show the complete movie? Pin
varcario119-Feb-11 19:37
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Generalwindows 64bit Pin
ducmanh8611-Feb-10 7:56
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GeneralRe: windows 64bit Pin
Member 112374918-Mar-10 23:16
MemberMember 112374918-Mar-10 23:16 
GeneralRe: windows 64bit Pin
ducmanh8610-Aug-10 11:47
Memberducmanh8610-Aug-10 11:47 
QuestionHow to Stop and pause movie Pin
Member 383892829-Jan-09 17:55
MemberMember 383892829-Jan-09 17:55 
GeneralMy vote of 1 Pin
Ikutsin7-Jan-09 2:57
MemberIkutsin7-Jan-09 2:57 
Questioncan not fine any .flv file to load Pin
sara saghi23-Dec-08 2:20
Membersara saghi23-Dec-08 2:20 
Generalc# and FLASH interfacing Pin
joshi aniruddha7-Jul-08 9:59
Memberjoshi aniruddha7-Jul-08 9:59 
QuestionCOM exception when load FLV file Pin
Mushtaque Nizamani8-Jun-08 23:44
MemberMushtaque Nizamani8-Jun-08 23:44 
QuestionAbout License Pin
Mushtaque Nizamani8-Jun-08 8:48
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Generali got Unspecified error Pin
Tejal Bhavsar4-Jun-08 1:59
MemberTejal Bhavsar4-Jun-08 1:59 
GeneralRe: i got Unspecified error Pin
Hypercube Softwares10-Sep-11 14:03
MemberHypercube Softwares10-Sep-11 14:03 
GeneralFunctio LoadVideo(string videoPath) is not working. [modified] Pin
Rasti Paluv25-May-08 5:36
MemberRasti Paluv25-May-08 5:36 
GeneralRe: Functio LoadVideo(string videoPath) is not working. Pin
Juba9-Nov-08 18:18
MemberJuba9-Nov-08 18:18 
Generali want read a file from recources(read byte of file ,not path) Pin
alirzn124-May-08 21:54
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GeneralCallFunction request string +XML object Pin
khoffmann7-May-08 5:56
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GeneralHelp me! I can't download source! Pin
ducmanh8629-Nov-07 8:32
Memberducmanh8629-Nov-07 8:32 

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