NullReferenceException when recording with NAudio (in c#)

Question

I am trying to record voice using NAudio in C# and I am stuck at two places:

1. A crash:

With a slightly modified form of code from THIS SO page, I am getting a NullReferenceException. Here is the crash log:

************** Exception Text **************
System.NullReferenceException: Object reference not set to an instance of an object.
   at NAudio.Wave.WaveIn.Callback(IntPtr waveInHandle, WaveMessage message, IntPtr userData, WaveHeader waveHeader, IntPtr reserved)
   at NAudio.Wave.WaveWindow.WndProc(Message& m)
   at System.Windows.Forms.Control.ControlNativeWindow.OnMessage(Message& m)
   at System.Windows.Forms.Control.ControlNativeWindow.WndProc(Message& m)
   at System.Windows.Forms.NativeWindow.Callback(IntPtr hWnd, Int32 msg, IntPtr wparam, IntPtr lparam)

and the code is:

using System;
using System.Windows.Forms;
using System.Threading;
using NAudio.Wave;

public class FOO
{
    static WaveIn s_WaveIn;

    [STAThread]
    static void Main(string[] args)
    {
        init();
        Application.Run();
    }

    public static void record()
    {
    while (true)
    {
        Console.WriteLine("Hit Enter to START Recording.\n");
        Console.ReadLine();

        s_WaveIn.StartRecording();

        Console.WriteLine("Hit Enter to STOP recording.\n");
        Console.ReadLine();

        s_WaveIn.StopRecording();
    }
    }

    public static void DeviceInit(int rate, int channels)
    {
    s_WaveIn = new WaveIn();
    s_WaveIn.WaveFormat = new WaveFormat(rate, channels);

    s_WaveIn.BufferMilliseconds = 1000;
    s_WaveIn.DataAvailable += new EventHandler<WaveInEventArgs>(SendCaptureSamples);
    }

    public static void init()
    {
    DeviceInit(44100, 2);

    Thread t1 = new Thread(delegate() {
        record();
        });
    t1.Start();
    }

    static void SendCaptureSamples(object sender, WaveInEventArgs e)
    {
    Console.WriteLine("Bytes recorded: {0}", e.BytesRecorded);
    }
}

Most of the times, this happens when I start recording THIRD time. Any idea what could be causing this?

*2. Modifying rate and channels at runtime.*

In my actual code, I am resetting wave format using s_WaveIn.WaveFormat = new WaveFormat(new_rate, new_channels); before calling StartRecording(). I am not calling Dispose() because that would require resetting the DataAvailable callback, and for that, I would need another message loop. Is this approach correct or should I first call Dispose and then reinitialize s_WaveIn with new format?

Thank you.

score 1 · Answer 1 · edited Sep 23 '14 at 09:53

1

Your Main method looks odd. What is the thread for?

Just use this:

[STAThread]
static void Main(string[] args)
{
    init();
    Application.Run();
}

Your init method also runs the application. Why?
Try changing it to:

public static void init()
{
    DeviceInit(44100, 2);

    Thread t1 = new Thread(delegate() {
        record();
    });
    t1.Start();
}

return; is not needed at the end of a method returning void.

edited Sep 23 '14 at 09:53

VMAtm

27,943
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answered Aug 18 '11 at 12:00

Daniel Hilgarth

171,043
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443

Thanks. Yes 'Application.Run' was not required in `init`. Fixed that. I reduced my original code keeping only the required things to post here on SO and missed to remove the thread creation in `Main`. Removed that also. But I believe, these changes have nothing to do with the crash I mentioned. Please correct me if I am wrong. Thank you. – John Smith Aug 18 '11 at 12:37

score 1 · Accepted Answer · answered Aug 23 '11 at 10:32

It Seems that DataAvailable callback is getting called even when buffer is null.

I modified a function in WaveIn.cs file and its working fine now. I am not sure if this is correct, but for now, this is working for me.

private void Callback(IntPtr waveInHandle, WaveInterop.WaveMessage message, IntPtr userData, WaveHeader waveHeader, IntPtr reserved)
{
    if (message == WaveInterop.WaveMessage.WaveInData)
    {
    GCHandle hBuffer = (GCHandle)waveHeader.userData;
    WaveInBuffer buffer = (WaveInBuffer)hBuffer.Target;
if (buffer != null)
{
    if (DataAvailable != null)
    {
    DataAvailable(this, new WaveInEventArgs(buffer.Data, buffer.BytesRecorded));
    }
    if (recording)
    {
    buffer.Reuse();
    }
}
else
{
    if (RecordingStopped != null)
    {
    RecordingStopped(this, EventArgs.Empty);
    }
}
}

}

Aleksandr Puchkov · Answer 3 · 2013-09-20T07:43:56.353

I got the same NullReferenceException. The author did not add lines to the proposed class WaveIn. Such use is not provided, as I understand it. Author library in the examples does not calls StopRecording (), and just stops to record incoming information, but continues to process it (for example to measure the volume), and calls StopRecording () for a complete stop to recive data to the data WaveIn. Thus, I believe that it is necessary to use a new WaveIn after calling StopRecording ().

score 0 · Answer 4 · edited Nov 14 '11 at 10:42

0

I think, it has to be done in this way:

GCHandle hBuffer = (GCHandle)waveHeader.userData;
WaveInBuffer buffer = (WaveInBuffer)hBuffer.Target;

if (buffer == null)
{
    return; // with this new line, everything works fine
}

if (DataAvailable != null)
{
    DataAvailable(this, new WaveInEventArgs(buffer.Data, buffer.BytesRecorded));
}

if (recording)
{
    buffer.Reuse();
}
else
{
    if (RecordingStopped != null)
    {
        RecordingStopped(this, EventArgs.Empty);
    }
}

edited Nov 14 '11 at 10:42

eeerahul

1,629
4
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answered Nov 14 '11 at 10:31

Tal Ben-Gal

1

Welcome on SO, here, it is a good practice to explain why to use your solution and not just how. That will make your answer more valuable and help further reader to have a better understanding of how you do it. I also suggest that you have a look on our FAQ : http://stackoverflow.com/faq. – ForceMagic Nov 06 '12 at 23:14

NullReferenceException when recording with NAudio (in c#)

4 Answers4