VB.NET LameMP3 Shell

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Introduction

The idea for LameShell came from my wish to be able to resample MP3 files in VB.NET. The goal was: "Whatever valid file goes in, out comes a 32kbit encoded MP3". I started looking around and I really didn’t like the solutions I found. You either had to deal with Interop or unmanaged code, it would cost, the interfaces where out of date or they where just too much. So I created this wrapper that allows me to have all sorts of status updates while Lame encodes the MP3. All you have to do in the application is supply the source file, the destination file and options you need.

Background

While there are some .NET wrappers around the LAME encoder lame_enc.dll, I decided to go a different route – a simple wrapper around lame.exe. There are so many options in there you could expose easily if you wanted to, or just directly type into your source if you have a simple goal – like I had. You can find out more about LAME here and you will need lame.exe to use this class. (lame.exe is not included with the source code)

Using the code

Using the code is very simple; you supply the filenames and options. Additionally, you can supply the path to lame.exe if it isn't in your application directory.

Dim WithEvents _lameShell As New LameShell
[...]
_lameShell.InFile = Application.StartupPath & "\test.mp3"
_lameShell.OutFile = Application.StartupPath & "\testOut.mp3"
_lameShell.Options = "-b 32"
_lameShell.Start()

Add some event handlers:

Private Sub _lameShell_Done() Handles _lameShell.Done
    lblFeedback.Text = "Done"
End Sub

Private Sub _lameShell_Canceled() Handles _lameShell.Canceled
    lblFeedback.Text = "Canceled/Error"
    pBar.Value = 0
End Sub

Private Sub _lameShell_Progress(ByRef Progress As LameProgress) _
                                      Handles _lameShell.Progress

    If pBar.Maximum <> Progress.FrameMax Then
        pBar.Value = 0
        pBar.Maximum = Progress.FrameMax
    Else
        pBar.Value = Progress.FrameCurrent
    End If
    lblFeedback.Text = Progress.PercentDone & "%" & " ETA:" & Progress.ETA

End Sub

That's all there is to it.

How it Works

Essentially, you create a new System.Diagnostics.Process with the needed ProcessStartInfo.

Private _startInfo As New ProcessStartInfo
[...]
'need this stuff to hide the window and redirect the output
_startInfo.FileName = "lame.exe"
_startInfo.UseShellExecute = False
_startInfo.RedirectStandardOutput = True
_startInfo.RedirectStandardError = True
_startInfo.CreateNoWindow = True

And you create a Reader in a different thread that keeps reading the output of lame.exe.

Private _lameThread As System.Threading.Thread
[...]
_lameThread = New System.Threading.Thread(AddressOf LameReader)
_lameThread.IsBackground = True
_lameThread.Name = "LameReader"
_lameThread.Start()
[...]

Private Sub LameReader()
    Dim oneLine As String
    _lameProcess.Start()
    
    oneLine = _lameProcess.StandardError.ReadLine()
    While Not oneLine Is Nothing
        '[...] Analyze Line
        
        'this call is blocking... thats why we are using a thread
        oneLine = _lameProcess.StandardError.ReadLine()
    End While
End Sub

Points of Interest

One thing I haven’t figured out is why the thread that is launched to read the info from lame.exe does not throw a Threading.ThreadAbortException when the application exits. According to MSDN, it should when IsBackround = true. For now, you are safe if you make sure to call LameShell.Cancel() if your application is closing.

Make sure not to depend on the Closing or Closed event of a form (like in the example) if you use Application.Exit anywhere. Those won’t fire if you use Application.Exit. That's why I would have liked the Threading.ThreadAbortException to fire to clean up on all circumstances.