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MP3 + CDG Karaoke Player


This is an MP3 + CDG file player application that parses CDG files and renders them in real time while an MP3 file is played. As a bonus, I included an MP3 + CDG to AVI conversion application which will not be discussed in this article.


After looking on the web for a while, I noticed that there was no .NET implementation for CDG file parsing available. One thing led to another, and I started porting over some C++ code that I found on Google Code. Once playback was established, I wanted pitch shifting. After that, I wanted rendering to AVI files. After that, I wanted transparency and background video for the AVI rendering...

Using the Code

This is the high level workflow for playing MP3 and CDG files together:

  1. Unzip the MP3 and CDG files into a temporary directory.
  2. Create a stream and open the CDG file.
  3. Determine the duration of the CDG file so that boundaries can be defined.
  4. Start playback of the MP3 file.
  5. Render the frame of the CDG file that is at the elapsed time position of the MP3 that is playing.

The main playback rendering block looks like this:

Private Sub Play()
      If mMP3Stream <> 0 AndAlso Bass.BASS_ChannelIsActive(mMP3Stream) = _
                    BASSActive.BASS_ACTIVE_PLAYING Then
      End If
      If mCDGFileName = "" Or mMP3FileName = "" Then
        MsgBox("Cannot find a CDG and MP3 file to play together.")
        Exit Sub
      End If
      mPaused = False
      mStop = False
      mFrameCount = 0
      mCDGFile = New CDGFile(mCDGFileName)
      Dim cdgLength As Long = mCDGFile.getTotalDuration
      Dim startTime As DateTime = Now
      Dim endTime = startTime.AddMilliseconds(mCDGFile.getTotalDuration)
      Dim millisecondsRemaining As Long = cdgLength
      While millisecondsRemaining > 0
        If mStop Then
          Exit While
        End If
        millisecondsRemaining = endTime.Subtract(Now).TotalMilliseconds
        Dim pos As Long = cdgLength - millisecondsRemaining
        While mPaused
          endTime = Now.AddMilliseconds(millisecondsRemaining)
        End While
        mFrameCount += 1
        mCDGWindow.PictureBox1.Image = mCDGFile.RGBImage
        mCDGWindow.PictureBox1.BackColor = CType(mCDGFile.RGBImage, Bitmap).GetPixel(1, 1)
        Dim myFrameRate As Single = Math.Round(mFrameCount / (pos / 1000), 1)
      End While
    Catch ex As Exception
    End Try
End Sub

Another challenge that presented itself was taking a multidimensional array of integers that was created from the CDG library and converting it into a bitmap. Here is the code that does the conversion:

Public ReadOnly Property RGBImage(Optional ByVal makeTransparent _
                As Boolean = False) As System.Drawing.Image
      Dim temp As New MemoryStream
        Dim i As Integer = 0
        For ri = 0 To CDG_FULL_HEIGHT - 1
          For ci = 0 To CDG_FULL_WIDTH - 1
            Dim ARGBInt As Integer = m_pSurface.rgbData(ri, ci)
            Dim myByte(3) As Byte
            myByte = BitConverter.GetBytes(ARGBInt)
            temp.Write(myByte, 0, 4)
      Catch ex As Exception
        'Do nothing (empty bitmap will be returned)
      End Try
      Dim myBitmap As Bitmap = StreamToBitmap(temp, CDG_FULL_WIDTH, CDG_FULL_HEIGHT)
      If makeTransparent Then
        myBitmap.MakeTransparent(myBitmap.GetPixel(1, 1))
      End If
      Return myBitmap
  End Get
End Property

Public Shared Function StreamToBitmap(ByRef stream As Stream, _
              ByVal width As Integer, ByVal height As Integer) As Bitmap
    'create a new bitmap
    Dim bmp As New Bitmap(width, height, PixelFormat.Format32bppArgb)
    Dim bmpData As BitmapData = bmp.LockBits(New Rectangle(0, 0, width, height), _
                                ImageLockMode.[WriteOnly], bmp.PixelFormat)
    stream.Seek(0, SeekOrigin.Begin)
    'copy the stream of pixel
    For n As Integer = 0 To stream.Length - 1
      Dim myByte(0) As Byte
      stream.Read(myByte, 0, 1)
      Marshal.WriteByte(bmpData.Scan0, n, myByte(0))
    Return bmp
End Function

The BASS Sound library was used for playback so the pitch of the MP3 could be changed in real time to adjust to the singer's key. Volume control was also needed to be able to mix volume levels from the MP3 with the singer's microphone. Here is the code that allows for the playback, volume control, and real-time pitch shifting:

Private Sub PlayMP3Bass(ByVal mp3FileName As String)
    If mBassInitalized OrElse Bass.BASS_Init(-1, 44100, _
                       BASSInit.BASS_DEVICE_DEFAULT, Me.Handle) Then
      mMP3Stream = 0
      mMP3Stream = Bass.BASS_StreamCreateFile(mp3FileName, 0, 0, _
                   BASSFlag.BASS_STREAM_DECODE Or _
      mMP3Stream = AddOn.Fx.BassFx.BASS_FX_TempoCreate(mMP3Stream, _
                   Or BASSFlag.BASS_SAMPLE_LOOP)
      If mMP3Stream <> 0 Then
        Bass.BASS_ChannelPlay(mMP3Stream, False)
        Throw New Exception(String.Format("Stream error: {0}", _
      End If
    End If
End Sub

Private Sub StopPlaybackBass()
    mMP3Stream = 0
    mBassInitalized = False
End Sub

Private Sub AdjustPitch()
    If mMP3Stream <> 0 Then
      Bass.BASS_ChannelSetAttribute(mMP3Stream, _
                BASSAttribute.BASS_ATTRIB_TEMPO_PITCH, nudKey.Value)
    End If
End Sub

Private Sub AdjustVolume()
    If mMP3Stream <> 0 Then
      Bass.BASS_ChannelSetAttribute(mMP3Stream, _
           BASSAttribute.BASS_ATTRIB_VOL, _
           If(trbVolume.Value = 0, 0, (trbVolume.Value / 100)))
    End If
End Sub

Points of Interest

I would like to thank:

  • Nikolay Nikolov for writing the original CDG code in C++
  • The authors of the BASS sound library
  • Anyone else whose code snippets I may have borrowed


  • 1.0 - Initial revision.

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