Flex Controlling Flash


This article focuses on controlling applications written Flash Player 8 and below that are loaded into Flex at runtime. If you want to read up on the various ways of doing this, I’ve written in the past how to control Flash Player 8SWF’s in Flash Player 9’s new AVM. This article specifically will talk about using Flash Player 8 content in a Flex 2 environment.

Before you read further, I strongly suggest you beg those in charge to allow you to re-write the AS2 content in AS3 (Flex 2 or Flash CS3). If that fails, keep reading.

Use Cases

Here are some common use cases where one would want to load Flash content into Flex content:

1. You have some existing Flash content that was previously written for a Flash Player before 9 (8, 7, or 6). This content could be a fully functioning application that has already proven itself by working successfully for awhile. Therefore, you’d like load it in atruntime and let it do it’s thing. There is no time, budget, and/or resources to re-write the content in AS3. An example would be a video player written for Flash Player 8/7/6 customers (those who don’t have 9).

2. You have some content that was created by another company or 3rd party tool that you want to integrate and possibly control. This could be SWF’s generated by Captivate, Connect, Swish, or perhaps even older versions of Flash. There technically are no “source files” so you couldn’t necessarily re-write the content, or said content just couldn’t be created in Flex in the first place.

3. You’re a Flex Developer and have no intentions of learning Flash. You’ve been ordered to load SWF’s that are not AS3 and control them.

4. Like #3, except you can’t find any Flash Developer contractors that are available. Imagine that.

For the record, all 3 are valiant efforts fraught with peril. Knowing this, you can re-attempt my advice to plead with management to abandon the course in folly, or grit yer teeth and git-r-done. I won’t re-iterate the problems here, you can read that in the above link. I will, however, give a quick refresher on what you can and can’t do.

First, none of the above scenarios allow embedding. If you do not have the source FLA created in Flash, with a valid copy of the Flash authoring tool (MX, MX 2004, 8, or CS3), you have no choice but to load this stuff at runtime. If you DID have a copy, you could embed it. Embedding AS2 SWF’s, however, removes all of your code. Thus, embedding AS2 applications won’t work. You don’t have these problems with AS3.

Second, loading AS2 / AS1 content at runtime creates a separate, special security sandbox for the SWF that’s being loaded. The DisplayObject is called AVM1Movie, and he’s an iron-clad, impenetrable black box. There is physically no way to breech it via ActionScript 3 to talk to it. You can, however, useliasons over / under the wall via ExternalInterface or LocalConnection. ExternalInterface sucks because it uses JavaScript. Every project I’ve ever done that incorporated JavaScript as a necessity added 1 more level of complexity, extended the debugging time in the project, and overall made it more challenging to make progress. Thus, while theAVM’s may be different versions, at least we’re coding in a semblance of the same language and runtime… well, more than JavaScript anyway. AS1 and he may be similar , but at least AS1 works the same in all browsers. You already have enough challenging things to worry about now that you are down this dangerous path; you don’t need another headache.

Third, your AS3 content cannot immediately “get rid of” AS2 / AS1 content in this AVM1Movie thing. Garbage Collection will get it when it feels like it. In the AS2 / AS1 AVM, removeMovieClip for the win! It works immediately, and while the actual RAM of the used variables may not go away, all media stops (sounds, video, animation) as opposed to AS3 where you have to be explicit to do so, not just remove it from theDisplayList.

Solution: A proxy SWF, aka proxy.swf, aka, a Flex liaison to AVM1 content.

Why a Proxy SWF

Since Flex 2 content (Flash Player 9, AS3 AVM+ SWF’s) cannot tell AVM1 SWF’s what to do, they use a guy on the inside, a proxy.swf, to act as agents for them in that world. The proxy.swf executes the orders that Flex issues, and these orders are communicated via LocalConnection.

That downside is, you still need to code this proxy.swf in AS2 or AS1 and compile it for at least the Flash Player 8 or below. You don’t necessarily need Flash to do this. You could use MTASC, PHP’s Ming, or JGenerator (I think what Lazslo uses?). I haven’t gotten this to work myself, but you could also possibly use the Flex 2 SDK’s mxmlc with the “as3” compiler option set to false, and the “es” option set to true. This should generate a Flash Player 9 SWF that uses the old AVM (so… technically AS2 like code that’s compiled to AS1 bytecode using a Flash Player 9 compiler).

…or, you could use my generic compiled example, and hope for the best.

If you want to do it right (keeping in mind “right” here means not-so-right since we shouldn’t be using older SWF content anyway), you typically tailor a proxy.swf for the particular content you are loading. For example, if you are loading Captivate SWF’s, you build a proxy SWF that can:

1. load in Captivate content
2. control Captivate content by their *hidden API
3. unload Captivate content

* For more info on hidden API, go here, scroll to the bottom and download the big ole PDF, search for “rdinfoFrameCount” which should take you to the “Controlling Adobe Captivate projects with variables” section.

This, as opposed to just my generic proxy that just accepts methods as strings and runs them much like JavaScript’s eval. That way, you can expose a loose API. You can’t share AS3 and AS2 interfaces, but we’re already past the point of IDE help here, so you’re really doing faith based coding at this point. Anyone whose ever used a dynamic language (as opposed to strict typing) shouldn’t have a problem with this. If you don’t code the proxySWF specifically for the content you are loading, it’s harder to debug, and basically really hard to identify which remote method invocations are failing.

I’ve provided 2 examples at the bottom of this article. One is my generic “I’ll run what you send me” one and the other is one built specifically to control the Flash 8 Video Player. While the generic can be something you can build upon to support your content, I highly recommend you follow how the video player one is built and build the proxy.swf specifically control a specific SWF.

How It Works

They both work the same way.

1. Flex SWFLoader loads an AVM1 proxy.swf
2. proxy.swf loads the content it’s supposed to use via loadMovie / MovieClipLoader
3. once the proxy.swf has loaded it’s content, it let’s Flex know
4. at this point, Flex can now tell the proxy.swf to do things with the content it’s loaded

These can sometimes breakdown. LocalConnections are by their very nature asynchronous. While you can create an instance immediately, that doesn’t mean it’s immediately available for use. For example, the AVM1 version of LocalConnection gives you a Boolean so you know if the send actually worked. If you get a true, it doesn’t mean it actually sent, just that the send operation itself “worked”. Amazingly f’ing useless. Send again? Hell… WHY NOT!?!

The AS3 version is different. You can get a few different types of exceptions from sending messages, such as ArgumentErrors and AsyncErrors. While the docs claim that your syntax can be correct, and it could be your request is just bigger than 40k, this is a crock. Even simple strings can just fail, and then magically work later. In short, LocalConnection is flaky; you’re code should compensate. If you need ensured communication, use ExternalInterface. That, however, has it’s own can of worms.

You do not have to use a SWFLoader. You could just a Loader, but since Flex is UIComponent based, SWFLoader is UIComponent based, so there you go.

The proxy examples I have both use MovieClipLoader. While you could simply use loadMovie, MovieClipLoader gives you more events to understand what’s happening with your loaded content. You don’t have to write polling code yourself; instead, you have dependable events that fire. The only one you really care about is onLoadInit. When that fires, whatever SWF you are loading can now be accessed by code in an ensured fashion. This is why you wait for that to fire as opposed to onLoadComplete.


All of this communication between Flash & Flex is done via 4 LocalConnections; 2 in Flex, 2 in Flash. LocalConnections are only 1 way. Meaning, you can only send messages or receive messages; not both. I typically use the “in_lc” and “out_lc” naming convention; feel free to make up your own. The Flex out_lc talks to the Flash in_lc. Vice versa, the Flash out_lc talks the Flex in_lc. The only thing uber confusing is that in Flex, the names are reversed. Since LocalConnections connect on a “connection name”, these 2 names need to be the same in Flash & Flex. So, in Flash I have:

LC_IN_NAME = “_JXLFlashProxy_IN”;
LC_OUT_NAME = “_JXLFlashProxy_OUT”;

And in Flex, I’ll have the same thing for values, but different things for the names; just to help easy the insanity.

public static const FLASH_LC_IN_NAME:String = “_JXLFlashProxy_IN”;
public static const FLASH_LC_OUT_NAME:String = “_JXLFlashProxy_OUT”;

The only difference is in Flex, you use the OUT name for your Flex “in” connection. Since Flash is sending messages out on the OUT connection, Flex needs its IN connection listening to the “Flash OUT” connection name. The reverse holds true for Flex sending messages. He’ll send them on Flash’s IN connection name.

To reiterate, these messages are asynchronous. They don’t arrive immediately, and you cannot return values. You can treat it like events, where the LocalConnection in Flash can send a message back to Flex with data, but unlike events, you can’t depend on this; some messages just don’t make it.

Dynamic Flash

If you are not familiar with Flash, you’ll notice that both AVM1 examples just dig right into the SWF they are loading. This is because there is no runtime strong-typing in pre-Flash Player 9. For example, if you look at the video_player2.fla, you’ll notice some methods on the main timeline. Flex asks the proxy.swf to call those methods since he can’t. Like a kingpin asking a thug to get his hands dirty. I can access those methods as if they were public class methods… even dynamically by concatenating strings together in Flash Player 8 and below. This is where a proxy.swf shines in that since it’s made in dynamic Flash land, it can play by dynamic Flash rules. This is important because sometimes you’ll be loading SWF’s that you don’t have code control over, and need to jury rig them to do things they weren’t originally intended to do.

Keep in mind a proxy.swf can do more than just dynamically call methods and set properties on a load SWF application. It can also affect the nature of that application. Since you are still in a prototype based language, an object’s prototype property is writable. Thus, even if you don’t have the source, and don’t feel like using aSWF decompiler to get some form of source, you can overwrite prototype objects that you introspect to force the SWF to do things you need.

…you know, in writing all of that, I’d much rather use a proxy.swf with ExternalInterface. As much as I hate JavaScript, it was pretty easy to break LocalConnection. Maybe next weekend…

Source Code

Video Player Flex Example – Example | View Source | ZIP

Generic Flex Example – Example | View Source | ZIP

16 Replies to “Flex Controlling Flash”

  1. Jesse

    Good article (the previous one too). We had to implement this very strategy on a big RIA we were developing where we had heaps (100’s – 1000’s) of F8 content we had to load and display. To make things even worse the F8 content was coming from another server from the app server flex was on ! So combine Flex sandbox, crossdomain, localconnection, …. = big head ache.

    We should have taken your advice and begged those in charge a bit more :)

  2. Hi Jesse,

    Interesting article as ever. I was just wondering what the advantage is of a separate proxy if it still has to be written in as2? Why not just put this code on the root of the legacy app your communicating with, or is this method exclusively for those times when you don’t have access to the as2 application source? Either way if you’re trying to control items in the legacy application you still have to look at the source to confirm the clip/function names so that you can perform actions on them (e.g. __vid.videoPlayer.stop(); )?


  3. If you have the source, totally agree. If you don’t, make a proxy (Captivate, Swish, awol contractor, etc.).

    Even SWF’s that don’t have the source can be debugged (sometimes) to see what’s inside of them. You can then set properties can call methods. Naturally this may not have been what the original author intended, but so be it, you have a job to do.

  4. Seen it. It’s an abstraction around ExternalInterface that I found un-fun to use. Although, to be fair, anytime you’re doing AMV+ to AVM communication, it’s not really fun to begin with.

  5. Hey Jesse,

    good article – had a couple of our local user group attendees ask about doing this for some older legacy content they have – will point them this way.

    See ya!

    Ps. Wish I had known you and Her majesty were in san fran last week – just got back myself.

  6. Jesse,
    Thanks you for the post, this proxy worked perfectly once I figured out what I was doing wrong :-) I greatly appreciate the post helped a lot. now to tweak it a little futher ;-)

    Thanks again

    Tim G.

  7. I’ve had to use a swf proxy in past projects but it doesn’t overcome the Flash 9 issue where you need to load the exact same as2component.swf multiple times at the same time (one initializes the other has issues).

    I did go the LC route but had some issues where LC wouldn’t work. This seemed even more problematic in the debug version of the player. Another issue is there is a data cap with how much you could send over 1 call.

    Rather then work around all the things I hit I went with FlashInterfaces. However, the documentation is slim, I found it impossible to get a hold of anyone for support/questions and it’s much harder to get things working then 1 would expect. For example, there are magic hidden variables, outdated source code examples and methods don

  8. Yo Jester,
    I must agree with you in recommending others to avoid this if possible. Of short my flex career this has easily been the most hideous experience.

    It thought i would receive too many nightmare memories if i read your code so pardon me if you have already implemented this but one thing that saved us network traffic was embedding the proxyswf into our flex avm1SWFPlayer component ;)

  9. Anyone know why this works perfectly running on the local machine but not on my web server, the proxy.swf is sending me back strings via LC saying videoPlayerStop OK but never removes the clip. So I know its getting to the portion of code on the proxy where it does the __vid.removeMovieClip but the clip is not actually being removed. So I believe LC is working fine just not removing the clip/adding new clip

  10. Jesse, first props: You are easily the most sensational and entertaining (albeit loquacious) writer of AS tech — thanks for the personality and expertise.

    So, dude, if you have a minute, tell me about garbage collection within this proxy schema when loading foreign video content. I have gone to the extent of nulling / removing / deleting / re-instantiating every object, variable, movieclip, and listener…all to no avail. I’ve done this all the way from the leaf movie to the SWFLoader. No dice. Though all references are gone, Flash continues to execute the foreign content. It’s as if the connection has been made in the Flex parent…? How to force Flash to collect this garbage? How to force it to close all data connections?

    I am to the point of seppuku because I know this has been and can be solved, but deadlines man, I am failing my master. Any comments would help — even mockery if it has a clue within would be appreciated.

    Keep up the bad-ass work. The virtual world is barely born.

  11. Great article for even a pseudo Flex programmer. I am having an issue implementing the proxy in a TitleWindow. I have it flying and rocking and rolling with content the first time I open the TitleWindow and view the movie. Once I close the window (and stop the movie) I cannot seem to get the proxy to reset itself. I open the window the second time and it just sits at main_state waiting for proxy to load. If I refresh the browser it works great again. Too bad that would erase all the form data that they are filling out!

    Any thoughts on this issue? From having your example in an Application and not a component I am concerned I am missing something about stopping and starting the proxy connection again!


  12. Great article.
    One question though, wouldn’t the use of LocalConnection limit the application to a single instance? If you run the video example twice then the second throws an error.

  13. Yes. LocalConnection is one connection. I believe the Flash / JavaScript kit in the past used multiple unique ID’s for the LocalConnection names set via JavaScript. This ensured unique connection names with the ability to launch multiple browser instances.

  14. Hi,

    I don’t think it works just as clean as it’s understood to. I’ve an AS2 app which in turns loads a lot of content (swfs, images). But the problem is that when this application is loaded inside an AS3 container, it goes bonkers. All the onLoadInit events stop responding and the contexts are all messed up. I’ll try setup a demo to show you what I mean.

    But if you’ve seen this happen already, please help.

  15. An important warning which I would have been VERY grateful to recive in time:

    LocalConnections are BUGGY as hell. don’t try to make more then 10 or so connects simultaniously or some of them will fail without proper errors. sometimes they crash your browser, too.

    more here: http://www.iherebydecree.com/archive/id/836

    good times (crazy laughter)…

Comments are closed.