Add sample-aware output stream wrapper and processor.

diff --git a/src/main/java/net/pterodactylus/sonitus/io/ProcessingOutputStream.java b/src/main/java/net/pterodactylus/sonitus/io/ProcessingOutputStream.java
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+++ b/src/main/java/net/pterodactylus/sonitus/io/ProcessingOutputStream.java
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+/*
+ * Sonitus - SampleOutputStream.java - Copyright © 2013 David Roden
+ *
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program.  If not, see <http://www.gnu.org/licenses/>.
+ */
+
+package net.pterodactylus.sonitus.io;
+
+import java.io.FilterOutputStream;
+import java.io.IOException;
+import java.io.OutputStream;
+
+/**
+ * {@link OutputStream} wrapper that is aware of channels and samples and can
+ * process samples before forwarding them to the wrapped output stream.
+ *
+ * @author <a href="mailto:bombe@pterodactylus.net">David ‘Bombe’ Roden</a>
+ */
+public abstract class ProcessingOutputStream extends FilterOutputStream {
+
+       /** The number of channels. */
+       private final int channels;
+
+       /** The current sample’s channel values. */
+       private int[] currentSamples;
+
+       /** The index of the current channel. */
+       private int currentSampleIndex;
+
+       /** The byte ofset of the current sample’s current channel. */
+       private int currentOffset;
+
+       /** The current sample’s channel value. */
+       private int currentSample;
+
+       /**
+        * Creates a new processing output stream. Sample values are always assumed to
+        * be 16 bits wide little-ending signed integers.
+        *
+        * @param outputStream
+        *              The output stream to wrap
+        * @param channels
+        *              The number of channels
+        */
+       public ProcessingOutputStream(OutputStream outputStream, int channels) {
+               super(outputStream);
+               this.channels = channels;
+               currentSamples = new int[channels];
+       }
+
+       //
+       // OUTPUTSTREAM METHODS
+       //
+
+       @Override
+       public void write(int data) throws IOException {
+               currentSample = ((currentSample >> 8) & 0xff) | (data << 8);
+               if (++currentOffset == 2) {
+                       currentOffset = 0;
+                       currentSamples[currentSampleIndex++] = currentSample;
+                       currentSample = 0;
+                       if (currentSampleIndex == channels) {
+                               currentSampleIndex = 0;
+                               int[] newSamples = processSamples(currentSamples);
+                               for (int sampleIndex = 0; sampleIndex < newSamples.length; ++sampleIndex) {
+                                       super.write(newSamples[sampleIndex] & 0xff);
+                                       super.write(newSamples[sampleIndex] >> 8);
+                               }
+                       }
+               }
+       }
+
+       @Override
+       public void write(byte[] buffer) throws IOException {
+               write(buffer, 0, buffer.length);
+       }
+
+       @Override
+       public void write(byte[] buffer, int offset, int length) throws IOException {
+               for (int index = 0; index < length; ++index) {
+                       write(buffer[offset + index]);
+               }
+       }
+
+       //
+       // SUBCLASS METHODS
+       //
+
+       /**
+        * Processes the given sample.
+        *
+        * @param samples
+        *              The channel values for a single sample
+        * @return The processed sample’s channel values
+        */
+       protected abstract int[] processSamples(int[] samples);
+
+}