Added events when fade-in/fade-out are complete

Docs/FadeInOutSampleProvider.md

@@ -14,6 +14,14 @@ var fade = new FadeInOutSampleProvider(audio, true);
 fade.BeginFadeIn(2000);
 ```
 
+After fade in is complete, `FadeInComplete` event is triggered:
+```c#
+fade.BeginFadeIn(2000);
+fade.FadeInComplete += (sender, e) => {
+    Console.WriteLine("Fade in was done!");
+};
+```
+
 Now we can pass our `FadeInOutSampleProvider` to an output device and start playing. We'll hear the audio fading in over the first two seconds.
 
 ```c#
@@ -28,6 +36,15 @@ At some point in the future, we might want to fade out, and we can trigger that
 fade.BeginFadeOut(2000);
 ```
 
+It also triggers `FadeOutComplete` event, when fade out is complete
+
+```c#
+fade.BeginFadeOut(2000);
+fade.FadeOutComplete += (sender, e) => {
+    Console.WriteLine("Fade out was done!");
+};
+```
+
 Once the audio has faded out, the `FadeInOutSampleProvider` continues to read from its source but emits silence until it reaches its end, or until you call `BeginFadeIn` again.
 
 ### Taking it further

NAudio.Core/Wave/SampleProviders/FadeInOutSampleProvider.cs

@@ -1,4 +1,6 @@
-namespace NAudio.Wave.SampleProviders
+using System;
+
+namespace NAudio.Wave.SampleProviders
 {
     /// <summary>
     /// Sample Provider to allow fading in and out
@@ -13,6 +15,16 @@ enum FadeState
             FadingOut,
         }
 
+        /// <summary>
+        /// Raised when scheduled fade-in is done
+        /// </summary>
+        public event EventHandler FadeInComplete;
+
+        /// <summary>
+        /// Raised when scheduled fade-out is done
+        /// </summary>
+        public event EventHandler FadeOutComplete;
+
         private readonly object lockObject = new object();
         private readonly ISampleProvider source;
         private int fadeSamplePosition;
@@ -108,6 +120,8 @@ private void FadeOut(float[] buffer, int offset, int sourceSamplesRead)
                 if (fadeSamplePosition > fadeSampleCount)
                 {
                     fadeState = FadeState.Silence;
+                    FadeOutComplete?.Invoke(this, EventArgs.Empty);
+
                     // clear out the end
                     ClearBuffer(buffer, sample + offset, sourceSamplesRead - sample);
                     break;
@@ -129,6 +143,8 @@ private void FadeIn(float[] buffer, int offset, int sourceSamplesRead)
                 if (fadeSamplePosition > fadeSampleCount)
                 {
                     fadeState = FadeState.FullVolume;
+                    FadeInComplete?.Invoke(this, EventArgs.Empty);
+
                     // no need to multiply any more
                     break;
                 }

NAudioTests/WaveStreams/FadeInOutSampleProviderTests.cs

@@ -120,5 +120,61 @@ public void BufferIsZeroedAfterFadeOut()
             Assert.AreEqual(20, read);
             Assert.AreEqual(0, buffer[0]);
         }
+
+        [Test]
+        public void FadeInCompleteInvoked()
+        {
+            // given
+            var source = new TestSampleProvider(10, 1); // 10 samples per second
+            source.UseConstValue = true;
+            source.ConstValue = 100;
+            var fade = new FadeInOutSampleProvider(source);
+            var fadeInsCount = 0;
+            fade.FadeInComplete += (sender, e) =>
+            {
+                fadeInsCount++;
+            };
+
+            // when
+            fade.BeginFadeIn(1000);
+
+            // then
+            float[] buffer = new float[20];
+            int read = fade.Read(buffer, 0, 20);
+            Assert.AreEqual(20, read);
+            Assert.AreEqual(0, buffer[0]); // start of fade-in
+            Assert.AreEqual(50, buffer[5]); // half-way
+            Assert.AreEqual(100, buffer[10]); // fully fade in
+            Assert.AreEqual(100, buffer[15]); // fully fade in
+            Assert.AreEqual(1, fadeInsCount); // we want one-shot event (when fade in was completed once)
+        }
+
+        [Test]
+        public void FadeOutCompleteInvoked()
+        {
+            // given
+            var source = new TestSampleProvider(10, 1); // 10 samples per second
+            source.UseConstValue = true;
+            source.ConstValue = 100;
+            var fade = new FadeInOutSampleProvider(source);
+            var fadeOutsCount = 0;
+            fade.FadeOutComplete += (sender, e) =>
+            {
+                fadeOutsCount++;
+            };
+
+            // when
+            fade.BeginFadeOut(1000);
+
+            // then
+            float[] buffer = new float[20];
+            int read = fade.Read(buffer, 0, 20);
+            Assert.AreEqual(20, read);
+            Assert.AreEqual(100, buffer[0]); // start of fade-out
+            Assert.AreEqual(50, buffer[5]); // half-way
+            Assert.AreEqual(0, buffer[10]); // fully fade out
+            Assert.AreEqual(0, buffer[15]); // fully fade out
+            Assert.AreEqual(1, fadeOutsCount); // we want one-shot event (when fade out was completed once)
+        }
     }
 }