使用录制的波形文件（NAudio）

Question

This is the code I use to record an audio file:

internal class AudioRecorder
{
    public WaveIn waveSource = null;
    public WaveFileWriter waveFile = null;
    public string RECORDING_PATH;

    public AudioRecorder(string fileName)
    {
        RECORDING_PATH = fileName;
    }

    public void Start()
    {
        waveSource = new WaveIn();
        waveSource.WaveFormat = new WaveFormat(44100, 1);
        waveSource.DeviceNumber = 0;
        waveSource.DataAvailable += new EventHandler<WaveInEventArgs>(waveSource_DataAvailable);
        waveSource.RecordingStopped += new EventHandler<StoppedEventArgs>(waveSource_RecordingStopped);

        waveFile = new WaveFileWriter(RECORDING_PATH, waveSource.WaveFormat);

        System.Timers.Timer t = new System.Timers.Timer(30000);

        t.Elapsed += new ElapsedEventHandler(Stop);

        waveSource.StartRecording();

        t.Start();


    }

    private void Stop(object sender, ElapsedEventArgs args)
    {
        waveSource.StopRecording();
    }

    private void waveSource_DataAvailable(object sender, WaveInEventArgs e)
    {
        if (waveFile != null)
        {
            waveFile.Write(e.Buffer, 0, e.BytesRecorded);
            waveFile.Flush();
        }
    }

    private void waveSource_RecordingStopped(object sender, StoppedEventArgs e)
    {
        if (waveSource != null)
        {
            waveSource.Dispose();
            waveSource = null;
        }

        if (waveFile != null)
        {
            waveFile.Dispose();
            waveFile = null;
        }

    }
}

In the main method I do:

AudioRecorder r = new AudioRecorder(dialog.FileName);
r.Start();
FileInfo file = new FileInfo(r.RECORDING_PATH);
// Do somehting with the recorded audio //

The problem is that when I do r.Start() the thread does not block and keeps running. So I get a corrupt file error. When I try things like Thread.Sleep to keep the thread waiting until recording finishes, this time the AudioRecorder code does not work well (ie recording never finishes).

Any ideas about what should I do to correctly wait the recording to finish so that I can safely use the recorded file ?

Answer 1

If you want to record for 30 seconds exactly, just call StopRecording in the DataAvailable event handler once you have enough data. There is absolutely no need for a complicated threading strategy. I do exactly this in the open source .NET voice recorder application .

Dispose the WaveFileWriter in the RecordingStopped event.

If you absolutely must have a blocking call, then use WaveInEvent, and wait on an event which is set in the RecordingStopped handler, as suggested by Rene. By using WaveInEvent, you remove the need for windows message pump to be operational.

Answer 2

You use a ManualResetEvent to wait for the Stop event to be called, giving other threads a change to proceed. I've only added the new bits...

internal class AudioRecorder
{  
    private ManualResetEvent mre = new ManualResetEvent(false);

    public void Start()
    {

        t.Start();
        while (!mre.WaitOne(200))
        {   
            // NAudio requires the windows message pump to be operational
            // this works but you better raise an event
            Application.DoEvents(); 
        }
    }

    private void Stop(object sender, ElapsedEventArgs args)
    {
        // better: raise an event from here!
        waveSource.StopRecording();
    }

    private void waveSource_RecordingStopped(object sender, EventArgs e)
    {
       /// ... your code here

       mre.Set();  // signal thread we're done!
    }

Answer 3

It is good idea to avoid any multi-threaded code if it is not required and Mark's answer is explaining this perfectly.

However, if you are writing a windows application and the requirement is to record 30 seconds than it is a must not to block a main thread in waiting (for 30 seconds). The new async C# feature can be very handy here. It will allow you to keep code logic straightforward and implement waiting in a very efficient way.

I have modified your code slightly to show how the async feature can be used in this case.

Here is the Record method:

    public async Task RecordFixedTime(TimeSpan span)
    {
        waveSource = new WaveIn {WaveFormat = new WaveFormat(44100, 1), DeviceNumber = 0};
        waveSource.DataAvailable += new EventHandler<WaveInEventArgs>(waveSource_DataAvailable);
        waveSource.RecordingStopped += new EventHandler<StoppedEventArgs>(waveSource_RecordingStopped);

        waveFile = new WaveFileWriter(RECORDING_PATH, waveSource.WaveFormat);

        waveSource.StartRecording();
        await Task.Delay(span);
        waveSource.StopRecording();
    }

Example of using Record from click handler of WPF app:

    private async void btnRecord_Click(object sender, RoutedEventArgs e)
    {
        try
        {
            btnRecord.IsEnabled = false;
            var fileName = Path.GetTempFileName() + ".wav";
            var recorder = new AudioRecorder(fileName);
            await recorder.RecordFixedTime(TimeSpan.FromSeconds(5));
            Process.Start(fileName);
        }
        finally
        {
            btnRecord.IsEnabled = true;
        }
    }

However, you have to watch out for timing here. Task.Delay does not guarantee that it will continue execution after the exact specified time span. You might get records slightly longer than is required.