Convert Raw PCM to wav or Mp3 file and save to Isolated storage wp7

public partial class IA_AudioPad : PhoneApplicationPage
    {

        private Microphone mic = Microphone.Default;
        private MemoryStream stream;
        byte[] buffer;
        double msElapsed;

        private DispatcherTimer timer = new DispatcherTimer();

        private const string ConnectionString = @"isostore:/DBs/IAssist_DB.sdf";

        public IA_AudioPad()
        {
            InitializeComponent();

            // Some necessary setup for our Microsoft.Xna.Framework.Audio.Microphone  
            mic.BufferDuration = TimeSpan.FromSeconds(1);
            buffer = new byte[mic.GetSampleSizeInBytes(mic.BufferDuration)];

            // Create the event handler.  I could have done an anonymous  
            // delegate here if I had so desired.  
            mic.BufferReady += handleBufferReady;


            timer.Interval = TimeSpan.FromMilliseconds(500);
            timer.Tick += new EventHandler(timer_Tick);
        }

        private void handleBufferReady(object sender, EventArgs e)
        {
            mic.GetData(buffer);
            stream.Write(buffer, 0, buffer.Length);
        }

        private void timer_Tick(object sender, EventArgs e)
        {
            msElapsed += 500;
            TimeSpan span = TimeSpan.FromMilliseconds(msElapsed);
            Timer.Text = String.Format("{0:d2} : {1:d2} : {2:d2}", span.Hours, span.Minutes, span.Seconds);
        }

        private void Record_Button_Click(object sender, EventArgs e)
        {
            msElapsed = 0;
            timer.Start();
            stream = new MemoryStream();
            mic.Start();
            Rec_Txt.Text = "Recording Note...";
            SetButtonStates(false, true, false);
        }

        private void Stop_Button_Click(object sender, EventArgs e)
        {
            timer.Stop();
            mic.Stop();
            Rec_Txt.Text = "Save Note";
            SetButtonStates(false, false, true);
        }

        private void Save_Btn_Click(object sender, EventArgs e)
        {
            string filename = string.Format("Media/Audio/{0}", AudPadTitle_Txt.Text);
            writeFile(stream, filename);
            AddAudpad_Det();
        }

        private void writeFile(MemoryStream s, string Filename)
        {
            using (var userStore = IsolatedStorageFile.GetUserStoreForApplication())
            {
                using (var file = userStore.OpenFile(Filename, FileMode.CreateNew))
                {
                    s.WriteTo(file);
                }
            }
        }