We can use extract method of the sound class in Flex 4/Flash 10, the method is able to extract raw wave data from SWF object. The technology is new feature, I have used this new technology recently, and I have got some result:
The extract method like a black box, we can't know what does it do.

1, Extract low sample rate sound will be get more samples, I can't understand that why like this. I know that it will transfer all kind of sample rate to 44.1KHz, but we can't know that how to transfer?

2, MPEG wave data is not bound to a single frame, so we need overlap some frames in a SWF sound what the sound compose of some frames. the overlap size is an experience value, in general, I set it as 7 frames. The value is depend your parse frames and detail extract algorithm sometimes. Anyway, 7 is my recommendation value.

3, This method can provide some very useful function with SoundMixer class for extend your application. For instance, show wave shape, add some effect, etc.
There is a sample for show waveform:
http://www.bytearray.org/?p=329

At last, I strong recommend an open source project, this project is a stream player based on Flex platform.
http://code.google.com/p/as3mp3streamplayer/

If you had deeply researched at this method, please communication with me. thank you!