private var myMic:Microphone;
private var nc:NetConnection;
private var ns:NetStream;

// get connected
private function get_connected():void {
    nc = new NetConnection();
    nc.connect("rtmp://your.domain.tld:1935");
}


// get audio source
private function init_audio():void {
    myMic = Microphone.getMicrophone();
}

// start recording
private function start_recording(fileName:String):void {
    ns = new NetStream(nc);
    ns.attachAudio(myMic);
    ns.publish(fileName, "record");
}

// stop recording
private function stop recording():void {
    ns.play(false); // flushes the recording buffer
    ns.close();
}