c# - 淡入/淡出声音

Question

我有一个无限循环播放的背景音。我希望它在用户按下按钮时淡出。

我尝试了以下方法:

• 使用 WaveStream 启动 DirectSoundOut
• 定时器改变 WaveChannel32 的音量。

问题:

• 在播放声音时改变音量会产生噪音。

有人知道更好的解决方案吗？

Answer 1

要执行平滑的淡入或淡出，您需要在样本级别执行此操作。然后将每个样本乘以逐渐增加或减少的数字。您正在使用 WaveChannel32，因此您的音频已经转换为 32 位 float 。然后，我将创建另一个 IWaveProvider 实现程序，负责执行淡入和淡出。通常它会通过样本不变，但在 Read 方法中，如果您处于淡入或淡出状态，它会乘以每个样本(如果是立体声，则成对)。

NAudio 1.5 中的 ISampleProvider 接口(interface)旨在使此类事情变得更加容易，因为它允许您将样本作为 32 位 float 进行处理，而不是实现 IWaveProvider，后者需要您将 byte[] 转换为 float[ ].这是我刚刚制作的用于淡入和淡出的 SampleProvider，我将把它包含在下一个 NAudio 中，并希望尽快在博客中介绍它。只需使用适当的淡入淡出持续时间调用 BeginFadeIn 或 BeginFadeOut。

public class FadeInOutSampleProvider : ISampleProvider
{
    enum FadeState
    {
        Silence,
        FadingIn,
        FullVolume,
        FadingOut,
    }

    private readonly object lockObject = new object();
    private readonly ISampleProvider source;
    private int fadeSamplePosition;
    private int fadeSampleCount;
    private FadeState fadeState;

    public FadeInOutSampleProvider(ISampleProvider source)
    {
        this.source = source;
        this.fadeState = FadeState.FullVolume;
    }

    public void BeginFadeIn(double fadeDurationInMilliseconds)
    {
        lock (lockObject)
        { 
            fadeSamplePosition = 0;
            fadeSampleCount = (int)((fadeDurationInMilliseconds * source.WaveFormat.SampleRate) / 1000);
            fadeState = FadeState.FadingIn;
        }
    }

    public void BeginFadeOut(double fadeDurationInMilliseconds)
    {
        lock (lockObject)
        {
            fadeSamplePosition = 0;
            fadeSampleCount = (int)((fadeDurationInMilliseconds * source.WaveFormat.SampleRate) / 1000);
            fadeState = FadeState.FadingOut;
        }
    }

    public int Read(float[] buffer, int offset, int count)
    {
        int sourceSamplesRead = source.Read(buffer, offset, count);
        lock (lockObject)
        {
            if (fadeState == FadeState.FadingIn)
            {
                FadeIn(buffer, offset, sourceSamplesRead);
            }
            else if (fadeState == FadeState.FadingOut)
            {
                FadeOut(buffer, offset, sourceSamplesRead);
            }
            else if (fadeState == FadeState.Silence)
            {
                ClearBuffer(buffer, offset, count);
            }
        }
        return sourceSamplesRead;
    }

    private static void ClearBuffer(float[] buffer, int offset, int count)
    {
        for (int n = 0; n < count; n++)
        {
            buffer[n + offset] = 0;
        }
    }

    private void FadeOut(float[] buffer, int offset, int sourceSamplesRead)
    {
        int sample = 0;
        while (sample < sourceSamplesRead)
        {
            float multiplier = 1.0f - (fadeSamplePosition / (float)fadeSampleCount);
            for (int ch = 0; ch < source.WaveFormat.Channels; ch++)
            {
                buffer[offset + sample++] *= multiplier;
            }
            fadeSamplePosition++;
            if (fadeSamplePosition > fadeSampleCount)
            {
                fadeState = FadeState.Silence;
                // clear out the end
                ClearBuffer(buffer, sample + offset, sourceSamplesRead - sample);
                break;
            }
        }
    }

    private void FadeIn(float[] buffer, int offset, int sourceSamplesRead)
    {
        int sample = 0;
        while (sample < sourceSamplesRead)
        {
            float multiplier = (fadeSamplePosition / (float)fadeSampleCount);
            for (int ch = 0; ch < source.WaveFormat.Channels; ch++)
            {
                buffer[offset + sample++] *= multiplier;
            }
            fadeSamplePosition++;
            if (fadeSamplePosition > fadeSampleCount)
            {
                fadeState = FadeState.FullVolume;
                // no need to multiply any more
                break;
            }
        }
    }

    public WaveFormat WaveFormat
    {
        get { return source.WaveFormat; }
    }
}