Is this a browser or Air based application?
The reason I ask is because Speex is only playable through an FLV container. It's a one way encode that is made to be streamed through a media player like FMS or Wowza. Here's what you need to do for both cases.
If browser based
There's no way to playing it locally. You're going to have to stream it to a media server which then returns an FLV file for you to play on the client.
If Air based
You can wrap the speex audio into an FLV container and play it locally. Use this library to write the FLV locally: http://www.zeropointnine.com/blog/simpleflvwriteras-as3-class-to-create-flvs/