Multimedia applications often have interactive elements based on video: For example, a pre-rendered 3D scene that moves according to a user’s interaction. The trick, in such a scene, is to play specific parts of the movie forward and backward to fake movement.

This sculpture has been rendered as a movie, with the camera panning 360˚around the object.
(Drag with the mouse to turn the object)

Embedding Animations

There are three basic ways to embed an animated scene into Flash:

• In the Flash Video format (FLV);
• As a sequence of images, e.g. PNG or JPEG;
• As a sequence of vector graphics.

The latter is often forgotten. Tools such as Cinema 4D’s FlashEx renderer can export a scene as a vector animation. If the scene doesn’t contain many objects and has simple texturing, a vector animation would probably be the way to go. The file size stays relatively small, plus the graphics are scalable.

A simple 3D object rendered as a vector sequence with FlashEx 2.
(Drag with the mouse to turn the object)

The other two methods, FLV and image sequences, are both pixel based, but have their own pros and cons. FLV has a decent quality/size ratio. Flash CS4 does not allow F4V files to be embedded directly, so the best codec is the older and less compressing On2 VP6. Interacting with FLV, e.g. jumping between frames quickly or playing it backward, is heavy on the processor. Presumably, the Flash Player has to jump to the nearest proceeding keyframe and process the changes to the current frame each time. On the other end of the spectrum is the image sequence. The compression is on a per-frame basis, so the overall file size will usually turn out much bigger. The display performance, however, is far better than FLV.

Eliminating the Cons

A combination of the reduced file size of FLV and the performance of an image sequence is possible, if the data gets decompressed on the client side. H.264 encoded video data could be sent through the wire and then be processed into an uncompressed image sequence before being displayed. I wrote a class named BitmapAnimation that parses each frame of a MovieClip (including any FLVs within) and adds it to an array of bitmap data. BitmapAnimation has the same methods as a MovieClip (gotoAndPlay, currentframe etc.), so the two can be interchanged. For instance, I was able to use a BitmapAnimation in place of a MovieClip to create a MovieMaterial in Papervision3d – polymorphism works.

When compared with simultaneously running FLVs, BitmapAnimations showed a 500% performance increase on my system. The difference was even bigger with the clips running backward. There may be a performance benefit in converting complicated vector animations to a BitmapAnimation before they are displayed. I have, however, not recently come across a scenario where a pure vector animation alone caused the frame rate to stagnate.

The MovieClip option cacheAsBitmap requires, to my understanding, the frame to be rendered in the Flash display list before it takes effect. This would be the only major difference to BitmapAnimation (where the image is rendered before being displayed). Enabling cacheAsBitmap on MovieClips containing FLV did not show a change in performance in my tests. Because a video is usually viewed once, it makes sense not to cache FLV by default.

There is one known drawback when using a BitmapAnimation: Depending on the size of the video and the client’s processor speed, the Flash Player could “freeze” for a few seconds while decompressing the video data. I created an additional class, where I lengthened the processing time by decompressing one frame per half-second. This would allow the video to be prepared in the background without noticeably slowing down the rest of the application. Delayed processing would work best during a loading sequence, where the video is loaded first, then converted to a BitmapAnimation, while the rest of the assets are being retrieved.

Usage

Simply pass a MovieClip to the draw method.

bitmapAnimation = new BitmapAnimation();
bitmapAnimation.draw(movieClip);
addChild(bitmapAnimation);

The imported bitmap data can be reused with multiple BitmapAnimations.

var bitmapAnimation1:BitmapAnimation = new BitmapAnimation();
bitmapAnimation1.draw(movieClip);
var bitmapAnimation2:BitmapAnimation = new BitmapAnimation(bitmapAnimation1.bitmapSequence);

Conclusions

Pre-rendering a complex MovieClip, such as embedded FLV, using the BitmapAnimation class, may likely show a performance increase. Also, this method may remove the need to embed an image sequence where display performance is an issue. Due to the computation time required for conversion, BitmapAnimations should not be used for long clips. Inputs and feature requests are welcome, just add a comment below.

Download the classes BitmapAnimation and DelayedBitmapAnimation.

Download the blimp example.

Screenshot from the 1995 racing game Destruction Derby

It seems that the graphics performance is comparable to games that came out in 1995 on the PC, before graphics hardware became widespread. Imagine running a game like Dark Forces or Destruction Derby inside the browser. In a nutshell, on today’s average computer, the Flash graphics performance is Quake 1 tops. Broad statements aside, it is important to know what code flies on the Flash Player when developing games and interactive applications.

I’d like to know what basic code will perform best in a given situation. Therefore, I have started to extract these parts of code from my projects and test them against alternative methods, attempting to quantify the execution speed on the AVM. Unlike Javascript, ActionScript usually runs on the same engine; This makes such specific tests worthwhile.

I have gathered performance tests from a couple of my projects and put them into the ActionScript Performance Wiki. It is open to anonymous editors, so anybody is free to add their own tests.

In my opinion, it looks like Flash will gradually return back to it’s roots as an animation tool. Unlike today, where it has become a multimedia behemoth in which entire sites are created. Flex and a new product named Flash Catalyst (formerly Thermo) will take over the rolls of creating user interaction. I got a preview copy of Catalyst and it looks pretty good. Page elements, and their states, can be assembled visually based on an imported Illustrator or Photoshop composition. It reminds me somewhat of Dreamweaver, but instead of HTML in creates MXML (the declarative language used in Flex).

I took a preview of Flex 4 (codename Gumbo) for a spin, but it still can’t keep up with the sheer awesomeness of FDT. I think Adobe should just buy FDT, employ all the Powerflasher dudes, mash the two products together, and give it a snappy name like Adobe Insane.

In one of the general sessions held on Tuesday it was mentioned that BlazeDS should soon be compatible with the .Net framework. I was exited about BlazeDS when I first heard of the product a couple months back, but my excitement eroded away like a soaked sandcastle when I heard it required Java. Nothing against Java of course, but the company I work for uses .Net. BlazeDS may yet make it onto the company servers.

One of the Max sessions showed a sneak peak of peer-to-peer capabilities in the Flash Player on the basis of RTMFP. A peer-to-peer mesh would open up some amazing data sharing possibilities. We could build a Skynet of SWFs! Historians in two hundred years would say things like: “At first it played simple animations and cheesy banners, but then it gained consciousness ant launched a nuclear attack”. We could also just use this technology for video streaming I guess.

I had a great time at Max, and I am looking forward to continuing my work as a Flash Developer with all the great new Tools coming up.

I made another attempt to get the Flash Tracer plugin from Sephiroth to work and I was successful (turns out my User Settings folder at work is saved on the 486 down the hall). With a few tweeks to the mm.cfg file I even get warnings about Security issues:

ErrorReportingEnable=1
TraceOutputFileEnable=1
PolicyFileLog=1
PolicyFileLogAppend=1

Apart from the dreadfully slow performance, I think this is the simplest way to debug a Flash App from within the browser.

A quick test gave the answer: Practically nill. 30 really long variable names compared to 30 short ones resulted in a file size difference of a measly 5 bytes.

Conclusion

For file size optimization, limiting the length of variable names should be considered an extreme measure. Rather, leave the code readable and optimize the images instead.

Update

Short variable names perform better than long ones. But again, not enough to make it worthwhile throughout the entire application.

The biggest issue I had was that the keyboard input would somehow get “reset” to the English layout. This means that anybody using a non-English keyboard would get strange results while typing. This keyboard bug has been known since at least 2005.

In the end I just loaded a dummy image into the background of the SWF instead of making it transparent. All the other browsers behaved fairly well with the WMODE setting.

If anybody else is having these issues, head over to bugzilla and vote for getting the bugs fixed.

In conclusion, consider WMODE=”transparent” a last resort for even the simplest Flash projects.

• Powerflasher SOS
• Flash Tracer Firefox Plugin
• Xray
• Thunderbolt

SOS looked sweet for a moment, because it used an XML Socket for the Logging statements. However I ran into some cross-domain issues on an external development server, so I put it aside. The Flash Tracer plugin for Firefox would have been sweeeet, but I gave up trying to get it work in Firefox 3. Xray is a debugging behemoth. I didn’t quit like having to include a connector component to my SWF. All these debuggers are pretty darn good, but they all involved some twisted procedures to get them up and running. I then stumbled across a super simple answer to my browser debugging issue. Why not just do what the Javascript guys do? Trace it out to Firebug like this:

ExternalInterface.call("console.log","test");

It’s so simple it can’t be wrong. There is just an issue that I have to decide if I want to use Flash’s built in trace function or the Firebug log while debugging. This however is taken care of buy Thunderbolt. It is a simple class that notices if Firebug is accessible and otherwise uses trace. Thunderbolt also has a “hide” option built in, for when the SWF goes live.

Conclusion

The Firebug / Thunderbolt combo is an elegant way to debug Flash content in both the Flash IDE and in Firefox. For a quick introduction to Thunderbolt, check out the Article 10 tips and tricks using ThunderBolt AS3, by Thunderbolt’s author Jens Krause.