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A full-duplex audio player in C# using the waveIn/waveOut APIs

, 31 Aug 2003
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An article on low-level audio capture and playback using the waveIn/waveOut APIs through P/Invoke in C#.

Sample Image - cswavrec.gif


As I already mentioned in my article A low-level audio player in C#, there are no built-in classes in the .NET framework for dealing with sound. This holds true not only for audio playback, but also for audio capture.

It should be noted, though, that the Managed DirectX 9 SDK does include classes for high-level and low-level audio manipulation. However, sometimes you don’t want your application to depend on the full DX 9 runtime, just to do basic sound playback and capture, and there are also some areas where Managed DirectSound doesn’t help at all (for example, multi-channel sound playback and capture).

Nevertheless, I strongly recommend you to use Managed DirectSound for sound playback and capture unless you have a good reason for not doing so.

This article describes a sample application that uses the waveIn and waveOut APIs in C# through P/Invoke to capture an audio signal from the sound card’s input, and play it back (almost) at the same time.

Using the code

The sample code reuses the WaveOutPlayer class from my article A low-level audio player in C#. The new classes in this sample are WaveInRecorder and FifoStream.

The FifoStream class extends System.IO.Stream to implement a FIFO (first-in first-out) of bytes. The overridden Write method adds data to the FIFO’s tail, and the Read method peeks and removes data from the FIFO’s head. The Length property returns the amount of buffered data at any time. Calling Flush will clear all pending data.

The WaveInRecorder class is analogous to the WaveOutPlayer class. In fact, if you look at the source files, you’ll notice that the implementations of these classes are very similar. As with WaveOutPlayer, the interface of this class has been reduced to the strict minimum.

Creating an instance of WaveInRecorder will cause the system to start recording immediately. Here’s the code that creates the WaveOutPlayer and WaveInRecorder instances.

private void Start()
        WaveLib.WaveFormat fmt = new WaveLib.WaveFormat(44100, 16, 2);
        m_Player = new WaveLib.WaveOutPlayer(-1, fmt, 16384, 3, 
                        new WaveLib.BufferFillEventHandler(Filler));
        m_Recorder = new WaveLib.WaveInRecorder(-1, fmt, 16384, 3, 
                        new WaveLib.BufferDoneEventHandler(DataArrived));

The WaveInRecorder constructor takes five parameters. Except for the last parameter, their meaning is the same as in WaveOutPlayer.

The first parameter is the ID of the wave input device that you want to use. The value -1 represents the default system device, but if your system has more than one sound card, then you can pass any number from 0 to the number of installed sound cards minus one, to select a particular device.

The second parameter is the format of the audio samples.

The third and forth parameters are the size of the internal wave buffers and the number of buffers to allocate. You should set these to reasonable values. Smaller buffers will give you less latency, but the captured audio may have gaps on it if your computer is not fast enough.

The fifth and last parameter is a delegate that will be called periodically as internal audio buffers are full of captured data. In the sample application we just write the captured data to the FIFO, like this:

private void DataArrived(IntPtr data, int size)
    if (m_RecBuffer == null || m_RecBuffer.Length < size)
        m_RecBuffer = new byte[size];
    System.Runtime.InteropServices.Marshal.Copy(data, m_RecBuffer, 0, size);
    m_Fifo.Write(m_RecBuffer, 0, m_RecBuffer.Length);

Similarly, the Filler method is called every time the player needs more data. Our implementation just reads the data from the FIFO, as shown below:

private void Filler(IntPtr data, int size)
    if (m_PlayBuffer == null || m_PlayBuffer.Length < size)
        m_PlayBuffer = new byte[size];
    if (m_Fifo.Length >= size)
        m_Fifo.Read(m_PlayBuffer, 0, size);
        for (int i = 0; i < m_PlayBuffer.Length; i++)
            m_PlayBuffer[i] = 0;
                                                 0, data, size);

Note that we declared the temporary buffers m_RecBuffer and m_PlayBuffer as member fields in order to improve performance by saving some garbage collections.

To stop streaming, just call Dispose on the player and capture objects. We also need to flush the FIFO so that the next time Start is called there is no residual data to play.

private void Stop()
    if (m_Player != null)
            m_Player = null;
    if (m_Recorder != null)
            m_Recorder = null;
    m_Fifo.Flush(); // clear all pending data


This sample demonstrates how to combine the waveIn and waveOut APIs in C#. As an exercise, you may want to combine this code with the audio effect framework in the article Programming Audio Effects in C#, to apply effects to a live audio input in real-time, although latency may be an issue for certain applications.


This article has no explicit license attached to it but may contain usage terms in the article text or the download files themselves. If in doubt please contact the author via the discussion board below.

A list of licenses authors might use can be found here


About the Author

Ianier Munoz
Web Developer
Luxembourg Luxembourg
Ianier Munoz lives in France and works as a senior consultant and analyst for an international consulting firm. His specialty is in multimedia applications, and he has authored some popular software, such as American DJ's Pro-Mix, Chronotron and Adapt-X.

Comments and Discussions

GeneralMy vote of 1 PinmemberMember 943842722-Sep-14 3:59 
QuestionPlz help : How to record audio buffer to a .wav file PinmemberMember 865071615-Jan-14 2:59 
BugFound a bug in WaveStream.cs, the class WaveStream PinmvpSergey Alexandrovich Kryukov18-Dec-13 16:27 
Questionnullreferenceexception PinmemberMember 877069515-Jun-13 10:32 
AnswerHow to fix WaveOut for Windows 64-bit (fix Null Reference exception) PinmemberKevin North20-May-13 9:21 
GeneralRe: How to fix WaveOut for Windows 64-bit (fix Null Reference exception) PinmemberBillWoodruff25-Jun-13 7:42 
QuestionHi Mr. Ianier Munoz Pinmemberahmed5_273-Feb-13 10:33 
QuestionHow to save in a .Wav file ? Pinmembersmartradio3-Nov-12 9:20 
QuestionException is thrown while you start recording on Win7 Pinmemberprajaaaa22-Oct-12 22:20 
AnswerRe: Exception is thrown while you start recording on Win7 PinmemberWes Jones1-Mar-13 12:58 
QuestionWhere the file is saved on your computer Pinmembernomigan7-Jul-12 13:22 
GeneralMy vote of 5 PinmemberFarhan Ghumra6-Jun-12 22:38 
BugHangs on Stop Pinmembershivbuyya10-Mar-12 22:09 
AnswerRe: Hangs on Stop PinmemberAyrA.ch10-Apr-12 11:48 
GeneralRe: Hangs on Stop Pinmembershivbuyya5-Oct-12 0:12 
GeneralRe: Hangs on Stop PinmemberAyrA.ch23-Oct-12 8:24 
AnswerRe: Hangs on Stop Pinmembervozmen26-Jan-13 5:02 
GeneralRe: Hangs on Stop Pinmemberbimbambumbum27-Mar-13 10:35 
AnswerRe: Hangs on Stop Pinmembervozmen27-Mar-13 11:53 
GeneralRe: Hangs on Stop Pinmemberbimbambumbum28-Mar-13 0:29 
GeneralRe: Hangs on Stop PinmemberAriadne15-May-14 6:25 
GeneralMy vote of 5 PinmemberMember 10944438-Jan-12 19:56 
Questionhow can I get the sound data? PinmemberMember 79558498-Aug-11 3:48 
AnswerRe: how can I get the sound data? PinmemberMember 40308897-Jan-12 23:24 
GeneralListen voice in a particular sound card Pinmembersawass24-May-11 6:17 
Generalhow to save the recorded file? Pinmemberahloon18-Apr-11 5:26 
GeneralRe: how to save the recorded file? PinmemberChristian_N21-Jun-12 12:45 
GeneralPause recording Pinmemberotto40009-Feb-11 0:39 
GeneralBytes in file stream have only values 0, 1 and 255 [modified] PinmemberPedjabla30-Jan-11 8:07 
GeneralMy vote of 3 Pinmembernil14018-Dec-10 19:05 
Answercswavrec_src_AnyCpu Pinmemberisme_enjoy1-Dec-10 22:08 
GeneralUrgent Help Skype Call Recording Using C# Pinmembersyed_developer25-Oct-10 22:45 
GeneralMy vote of 5 PinmemberPsyris_25-Oct-10 6:36 
GeneralCompact Framework Pinmemberershad121-Oct-10 1:31 
GeneralDoes not work in x64 Pinmemberyasaralper29-Aug-10 3:15 
GeneralRe: Does not work in x64 PinmemberNAMEJ12-Mar-11 1:30 
I had a similar problem. It is because of definitions of native functions. For example:
public static extern int waveInOpen(out IntPtr phwi, int uDeviceID, WaveFormat lpFormat, WaveDelegate dwCallback, int dwInstance, int dwFlags);

is on MSDN defined as:
MMRESULT waveInOpen(
  LPHWAVEIN       phwi,      
  UINT_PTR       uDeviceID,  
  LPWAVEFORMATEX pwfx,       
  DWORD_PTR      dwCallback, 
  DWORD_PTR      dwCallbackInstance, 
  DWORD          fdwOpen     

On x86 it is ok, but on x64 it isn´t. Definition should be something like this:
public static extern int waveInOpen(out IntPtr phwi, UIntPtr uDeviceID, WaveFormat lpFormat, WaveDelegate dwCallback, IntPtr dwInstance, int dwFlags);

And it is similar for other functions. See:[^] and[^].
GeneralRe: Does not work in x64 Pinmemberyasaralper13-Mar-11 11:36 
GeneralRe: Does not work in x64 PinmemberRoey C19-Jan-12 8:57 
GeneralRe: Does not work in x64 - example is in error Pinmemberjcameron2330-Nov-12 14:45 
Generaltwo USB-soundcards cause problems PinmemberMember 402255423-Aug-10 21:40 
QuestionI need digitized data [modified] Pinmemberrrsharif16-Aug-10 23:54 
GeneralC# saving Wav PinmemberFahed Al Daye1-Jun-10 7:56 
Questionis it possible to duplicate channels ? Pinmembersr_dusad13-May-10 20:43 
Questionquestion Pinmemberfribe20-Apr-10 6:23 
Generaldelay Pinmemberjachuuu22-Mar-10 4:18 
GeneralRe: delay Pinmemberk6343002745-Apr-11 17:18 
Generalvs 2010... Pinmembergrummbunger12-Mar-10 14:29 
Generalecho Pinmemberxiscoverso9-Jan-10 2:05 
GeneralRe: echo Pinmemberalex let12-Feb-10 7:13 
GeneralDoesn't work if running on a 64 bit application. Pinmembercoder25519-Dec-09 10:25 

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