Compressing BitmapData - actionscript

Question

The situation is this:
I've written a simple MovieClip replacement that converts an existing imported MovieClip to a sequence of BitmapData. This removes the requirement for Flash to render vector data in the MovieClip on each frame.
But BitmapData has a huge memory footprint. I've tried converting the BitmapData to a ByteArray and using the compress() method. This results in a significantly smaller memory footprint. But it has proven impractical. For each redraw, I tried uncompressing()'ing the ByteArray, then using SetPixels to blit the data to the screen, then re-compressing() the frame. This works but is terribly slow.
So I was wondering if anybody else has an approach I could try. In Flash, is it possible to compress bitmap data in memory and quickly blit it to the screen?
I wonder how native animated GIFs work in Flash. Does it uncompress them to BitmapData behind the scenes, or is frame decompression done on the fly?
Perhaps there is an Alchemy project that attempts to blit compressed images?
Thanks for any advice you can offer :)

Answer 1

#thienhaflash's response is good but has aged a year and since then Flash Player and AIR Runtime have expanded their capabilities. Today I stumbeled on this little tidbit from Adobe's AS3 Guide. As of player 11.3 there are native image compression techniques available. Here's a snippet:
// Compress a BitmapData object as a JPEG file.
var bitmapData:BitmapData = new BitmapData(640,480,false,0x00FF00);
var byteArray:ByteArray = new ByteArray();
bitmapData.encode(new Rectangle(0,0,640,480), new flash.display.JPEGEncoderOptions(), byteArray);
Not sure about the practicality for blitting but it's nice that it can be done natively.

Answer 2

For memory reservation you need to think twice before convert a MovieClip to a Bitmap sequence. Is it really that need ? Can you break things down as there are several things (like the background) is static (or just moving around) why don't cache bitmap for each elements instead of one big Bitmap sequence ?
I usually used AnimatedBitmap (the name for bitmap sequence alternative for a MovieClip) only for small size animated icons, and other heavy calculation stuffs (like fire / smoke effects ...). Just break things down as much as you can !
As far as i know, there are no way to compress the memory used by a BitmapData located in the memory and there are nothing related to Alchemy could help improve memory used in this case.
Animated GIF won't works in Flash natively, you will need some library to do that. Search for AnimatedGIF as3 library from bytearray.com, actually the library just read the gif file in raw byteArray and convert to an animatedBitmap just like how you've done.

Answer 3

this is an old question, but there is recent info on this : jackson Dunstan has had a run with bitmapdatas and it turns out that Bitmap data obtained from compressed sources will "deflate" after some time unused.
here are the articles : http://jacksondunstan.com/articles/2112, and the two referred at the beginning of it.
So you could absolutely do something like :
var byteArray:ByteArray = new ByteArray();
myBitmapData.encode(new Rectangle(0,0,640,480), new flash.display.JPEGEncoderOptions(), byteArray);
var loader = new Loader();
loader.addEventListener(Event.COMPLETE, function(_e:Event):void{
if(loader.content is Bitmap){
myBitmapData.dispose()
myBitmapData= Bitmap(loader.content).bitmapData;
}
});
loader.loadBytes(byteArray);
I'm not sure if it would work as is, and you definitely want to handle your memory better. but now, myBitmapData will be uncompressed when you try to read from it, and then re-compressed when you don't use it for about ten seconds.