RecordAudioFileLinuxAlsa.md

Record an Audio File on Linux with ALSA

The NAudio.Alsa package provides AlsaIn, an IWaveIn that records from an ALSA capture device. Add the package (the runtime needs libasound — sudo apt install libasound2):

dotnet add package NAudio.Alsa

Recording follows the standard NAudio pattern: set the WaveFormat, subscribe to DataAvailable and write the captured bytes to a WaveFileWriter, then StartRecording / StopRecording. AlsaIn raises RecordingStopped once the capture thread has finished, which is the safe point to dispose the writer.

using NAudio.Wave;
using NAudio.Wave.Alsa;

var waveFormat = new WaveFormat(44100, 16, 2);
var writer = new WaveFileWriter("recorded.wav", waveFormat);

using var input = new AlsaIn();           // or new AlsaIn("hw:0")
input.WaveFormat = waveFormat;

input.DataAvailable += (sender, a) =>
{
    writer.Write(a.Buffer, 0, a.BytesRecorded);
};

input.RecordingStopped += (sender, a) =>
{
    writer.Dispose();
    writer = null;
};

input.StartRecording();
Thread.Sleep(5000);                       // record for 5 seconds
input.StopRecording();

Pick a specific capture device by passing an ALSA PCM name to the constructor, or enumerate them:

foreach (var device in AlsaDeviceEnumerator.GetCaptureDevices())
{
    Console.WriteLine($"{device.Name} - {device.Description}");
}
// using var input = new AlsaIn("hw:1");

The WaveInEventArgs buffer is reused on the next callback, so write or copy it before the handler returns. The recording format must be a PCM or IEEE-float WaveFormat (8/16/24/32-bit PCM or 32-bit float): a WaveFormat with no ALSA mapping throws NotSupportedException from StartRecording, and a device that cannot be opened with the requested parameters throws an AlsaException. Prefer default or a plughw: device for arbitrary rates/formats — a bare hw: device only accepts formats and sample rates it natively supports.