AsioPlayback.md

Playback with ASIO

NAudio 3 introduces AsioDevice, a redesigned ASIO API that handles playback, recording, and duplex I/O through three explicit configuration modes. This article covers playback only — see AsioRecording and AsioDuplex for the other modes, and AsioMigration if you're moving from the legacy AsioOut class.

ASIO is the low-latency driver format supported by most professional Windows audio interfaces and many DAW applications. To use it you need a soundcard with an ASIO driver installed. If your hardware doesn't ship one, ASIO4ALL is a free WDM-to-ASIO shim that works with most consumer soundcards.

Open the device

Enumerate the installed ASIO drivers and open one by name:

foreach (var name in AsioDevice.GetDriverNames())
    Console.WriteLine(name);

using var device = AsioDevice.Open("Focusrite USB ASIO");

AsioDevice implements IDisposable. Always wrap it in a using statement (or call Dispose explicitly) — the underlying COM driver doesn't release until you do.

Configure for playback

Pass an IWaveProvider (or wrap an ISampleProvider via .ToWaveProvider()) to InitPlayback:

using var reader = new AudioFileReader("music.wav");

device.InitPlayback(new AsioPlaybackOptions
{
    Source = reader
});

The source's sample rate must be one the driver supports — device.IsSampleRateSupported(rate) answers that. The source's channel count must equal the number of output channels you select (defaults to a contiguous range starting at channel 0).

Select output channels

AsioPlaybackOptions.OutputChannels is an int[] of physical channel indices. Source channel n is routed to physical output OutputChannels[n]. The array can be non-contiguous — there's no ChannelOffset style restriction.

// Stereo source → physical outputs 4 and 5 (zero-based).
device.InitPlayback(new AsioPlaybackOptions
{
    Source = reader,
    OutputChannels = [4, 5]
});

To send to every available output:

OutputChannels = device.Capabilities.AllOutputChannels

device.Capabilities.NbOutputChannels tells you how many physical outputs the driver exposes; device.Capabilities.OutputChannelInfos[i].name gives a human-readable name for each.

See AsioChannelMapping for more channel-routing patterns.

Start and stop

device.Start();
// ...
device.Stop();

Stop() raises the Stopped event on the captured SynchronizationContext (the thread you constructed the device on, typically the UI thread). The handler may safely call Dispose() — the device is fully off the ASIO callback thread by the time Stopped fires.

By default the device auto-stops when the source reaches end-of-stream. Set AutoStopOnEndOfStream = false in the options if you want the device to keep running on silent buffers after the source runs dry (e.g. so you can swap providers).

Handle errors and end-of-stream

device.Stopped += (sender, e) =>
{
    if (e.Exception is not null)
        Console.WriteLine($"ASIO faulted: {e.Exception.Message}");
    else
        Console.WriteLine("Playback complete.");
};

Stopped fires exactly once per Start/Stop cycle, with e.Exception populated if the source threw or the driver reported an unrecoverable fault.

Recover from driver settings changes

If the user opens the driver's control panel and changes the sample rate (or any other setting), the driver fires a reset request. The recommended response:

device.DriverResetRequest += (_, _) =>
{
    device.Stop();
    device.Reinitialize();
    device.Start();
};

Reinitialize() re-applies the most recent InitPlayback options against the (possibly changed) driver state — see AsioDriverReset for the full pattern.

Buffer size and latency

AsioPlaybackOptions.BufferSize accepts a frame count, or null to use the driver's preferred size. Smaller buffers mean lower latency but more callback overhead. The actual latencies in frames are reported by device.OutputLatencySamples after InitPlayback succeeds.

The buffer-switch callback runs on the ASIO driver's real-time thread, so any IWaveProvider in your chain must produce samples within the buffer duration. Allocations and slow I/O on that thread cause glitches.

Full example

using NAudio.Wave;

using var reader = new AudioFileReader("music.wav");
using var device = AsioDevice.Open(AsioDevice.GetDriverNames()[0]);

device.InitPlayback(new AsioPlaybackOptions
{
    Source = reader,
    OutputChannels = [0, 1]
});

var done = new ManualResetEventSlim();
device.Stopped += (_, _) => done.Set();
device.Start();
done.Wait();