Add support for rechunking fixed-sample-size data.

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Created by MOE: https://github.com/google/moe
MOE_MIGRATED_REVID=121565738

library/src/main/java/com/google/android/exoplayer/extractor/mp4/FixedSampleSizeRechunker.java

+/*
+ * Copyright (C) 2016 The Android Open Source Project
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package com.google.android.exoplayer.extractor.mp4;
+
+import com.google.android.exoplayer.C;
+import com.google.android.exoplayer.util.Util;
+
+/**
+ * Rechunks fixed sample size media in which every sample is a key frame (e.g. uncompressed audio).
+ */
+/* package */ final class FixedSampleSizeRechunker {
+
+  /**
+   * The result of a rechunking operation.
+   */
+  public static final class Results {
+
+    public final long[] offsets;
+    public final int[] sizes;
+    public final int maximumSize;
+    public final long[] timestamps;
+    public final int[] flags;
+
+    private Results(long[] offsets, int[] sizes, int maximumSize, long[] timestamps, int[] flags) {
+      this.offsets = offsets;
+      this.sizes = sizes;
+      this.maximumSize = maximumSize;
+      this.timestamps = timestamps;
+      this.flags = flags;
+    }
+
+  }
+
+  /**
+   * Maximum number of bytes for each buffer in rechunked output.
+   */
+  private static final int MAX_SAMPLE_SIZE = 8 * 1024;
+
+  /**
+   * Rechunk the given fixed sample size input to produce a new sequence of samples.
+   *
+   * @param fixedSampleSize Size in bytes of each sample.
+   * @param chunkOffsets Chunk offsets in the MP4 stream to rechunk.
+   * @param chunkSampleCounts Sample counts for each of the MP4 stream's chunks.
+   * @param timestampDeltaInTimeUnits Timestamp delta between each sample in time units.
+   */
+  public static Results rechunk(int fixedSampleSize, long[] chunkOffsets, int[] chunkSampleCounts,
+      long timestampDeltaInTimeUnits) {
+    int maxSampleCount = MAX_SAMPLE_SIZE / fixedSampleSize;
+
+    // Count the number of new, rechunked buffers.
+    int rechunkedSampleCount = 0;
+    for (int chunkSampleCount : chunkSampleCounts) {
+      rechunkedSampleCount += Util.ceilDivide(chunkSampleCount, maxSampleCount);
+    }
+
+    long[] offsets = new long[rechunkedSampleCount];
+    int[] sizes = new int[rechunkedSampleCount];
+    int maximumSize = 0;
+    long[] timestamps = new long[rechunkedSampleCount];
+    int[] flags = new int[rechunkedSampleCount];
+
+    int originalSampleIndex = 0;
+    int newSampleIndex = 0;
+    for (int chunkIndex = 0; chunkIndex < chunkSampleCounts.length; chunkIndex++) {
+      int chunkSamplesRemaining = chunkSampleCounts[chunkIndex];
+      long sampleOffset = chunkOffsets[chunkIndex];
+
+      while (chunkSamplesRemaining > 0) {
+        int bufferSampleCount = Math.min(maxSampleCount, chunkSamplesRemaining);
+
+        offsets[newSampleIndex] = sampleOffset;
+        sizes[newSampleIndex] = fixedSampleSize * bufferSampleCount;
+        maximumSize = Math.max(maximumSize, sizes[newSampleIndex]);
+        timestamps[newSampleIndex] = (timestampDeltaInTimeUnits * originalSampleIndex);
+        flags[newSampleIndex] = C.BUFFER_FLAG_KEY_FRAME;
+
+        sampleOffset += sizes[newSampleIndex];
+        originalSampleIndex += bufferSampleCount;
+
+        chunkSamplesRemaining -= bufferSampleCount;
+        newSampleIndex++;
+      }
+    }
+
+    return new Results(offsets, sizes, maximumSize, timestamps, flags);
+  }
+
+}