Having had a quick look at the Flex docs I can't seem to find any reference to providing audio content to be played from a custom (possibly encrypted - don't worry, it's not that evil) container format. Is this possible and if so, could someone point me in the right direction.
Or if that's not possible, some way to hook into the disk/network (disk is much more important in this case) I/O of the sound playing mechanism to provide a supported container in memory from a custom wrapper.
Since Flash Player 10, it's posible to write PCM / raw audio data to a Sound Object.
Basically, you call play on an "empty" Sound Object and it will start dispatching periodically a SampleDataEvent, requesting data. You then can write to the audio stream through the data ByteArray exposed by the event object.
http://www.adobe.com/devnet/flash/articles/dynamic_sound_generation/index.html
Also, if you're interested in good articles and reference for audio programming in Actionscript, you might want to check out Andre Michelle's stuf:
A flash.media.Sound must either be:
There currently is no provision for directly piping mp3 (or aac, or video) data to a any "media" object, such as Sound. You can only get the Sound object to download the data for itself. There are people who are upset about this, including myself; you are not alone!
I say "at this stage" because it's not unthinkable that Adobe will update the API to make this possible in a future version. For the now, you're best to go with the decoding-to-a-dynamic-sound workaround mentioned by Juan, if you really need to be able to do this.
And post a feature request at Adobe's bug tracker, or vote on an existing one!