1 files changed, 136 insertions, 0 deletions
diff --git a/mobile/android/exoplayer2/src/main/java/org/mozilla/thirdparty/com/google/android/exoplayer2/extractor/mp3/VbriSeeker.java b/mobile/android/exoplayer2/src/main/java/org/mozilla/thirdparty/com/google/android/exoplayer2/extractor/mp3/VbriSeeker.java
new file mode 100644
index 0000000000..8bb142f496
--- /dev/null
+++ b/mobile/android/exoplayer2/src/main/java/org/mozilla/thirdparty/com/google/android/exoplayer2/extractor/mp3/VbriSeeker.java
@@ -0,0 +1,136 @@
+/*
+ * 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 org.mozilla.thirdparty.com.google.android.exoplayer2.extractor.mp3;
+
+import androidx.annotation.Nullable;
+import org.mozilla.thirdparty.com.google.android.exoplayer2.C;
+import org.mozilla.thirdparty.com.google.android.exoplayer2.extractor.MpegAudioHeader;
+import org.mozilla.thirdparty.com.google.android.exoplayer2.extractor.SeekPoint;
+import org.mozilla.thirdparty.com.google.android.exoplayer2.util.Log;
+import org.mozilla.thirdparty.com.google.android.exoplayer2.util.ParsableByteArray;
+import org.mozilla.thirdparty.com.google.android.exoplayer2.util.Util;
+
+/** MP3 seeker that uses metadata from a VBRI header. */
+/* package */ final class VbriSeeker implements Seeker {
+
+  private static final String TAG = "VbriSeeker";
+
+  /**
+   * Returns a {@link VbriSeeker} for seeking in the stream, if required information is present.
+   * Returns {@code null} if not. On returning, {@code frame}'s position is not specified so the
+   * caller should reset it.
+   *
+   * @param inputLength The length of the stream in bytes, or {@link C#LENGTH_UNSET} if unknown.
+   * @param position The position of the start of this frame in the stream.
+   * @param mpegAudioHeader The MPEG audio header associated with the frame.
+   * @param frame The data in this audio frame, with its position set to immediately after the
+   *     'VBRI' tag.
+   * @return A {@link VbriSeeker} for seeking in the stream, or {@code null} if the required
+   *     information is not present.
+   */
+  public static @Nullable VbriSeeker create(
+      long inputLength, long position, MpegAudioHeader mpegAudioHeader, ParsableByteArray frame) {
+    frame.skipBytes(10);
+    int numFrames = frame.readInt();
+    if (numFrames <= 0) {
+      return null;
+    }
+    int sampleRate = mpegAudioHeader.sampleRate;
+    long durationUs = Util.scaleLargeTimestamp(numFrames,
+        C.MICROS_PER_SECOND * (sampleRate >= 32000 ? 1152 : 576), sampleRate);
+    int entryCount = frame.readUnsignedShort();
+    int scale = frame.readUnsignedShort();
+    int entrySize = frame.readUnsignedShort();
+    frame.skipBytes(2);
+
+    long minPosition = position + mpegAudioHeader.frameSize;
+    // Read table of contents entries.
+    long[] timesUs = new long[entryCount];
+    long[] positions = new long[entryCount];
+    for (int index = 0; index < entryCount; index++) {
+      timesUs[index] = (index * durationUs) / entryCount;
+      // Ensure positions do not fall within the frame containing the VBRI header. This constraint
+      // will normally only apply to the first entry in the table.
+      positions[index] = Math.max(position, minPosition);
+      int segmentSize;
+      switch (entrySize) {
+        case 1:
+          segmentSize = frame.readUnsignedByte();
+          break;
+        case 2:
+          segmentSize = frame.readUnsignedShort();
+          break;
+        case 3:
+          segmentSize = frame.readUnsignedInt24();
+          break;
+        case 4:
+          segmentSize = frame.readUnsignedIntToInt();
+          break;
+        default:
+          return null;
+      }
+      position += segmentSize * scale;
+    }
+    if (inputLength != C.LENGTH_UNSET && inputLength != position) {
+      Log.w(TAG, "VBRI data size mismatch: " + inputLength + ", " + position);
+    }
+    return new VbriSeeker(timesUs, positions, durationUs, /* dataEndPosition= */ position);
+  }
+
+  private final long[] timesUs;
+  private final long[] positions;
+  private final long durationUs;
+  private final long dataEndPosition;
+
+  private VbriSeeker(long[] timesUs, long[] positions, long durationUs, long dataEndPosition) {
+    this.timesUs = timesUs;
+    this.positions = positions;
+    this.durationUs = durationUs;
+    this.dataEndPosition = dataEndPosition;
+  }
+
+  @Override
+  public boolean isSeekable() {
+    return true;
+  }
+
+  @Override
+  public SeekPoints getSeekPoints(long timeUs) {
+    int tableIndex = Util.binarySearchFloor(timesUs, timeUs, true, true);
+    SeekPoint seekPoint = new SeekPoint(timesUs[tableIndex], positions[tableIndex]);
+    if (seekPoint.timeUs >= timeUs || tableIndex == timesUs.length - 1) {
+      return new SeekPoints(seekPoint);
+    } else {
+      SeekPoint nextSeekPoint = new SeekPoint(timesUs[tableIndex + 1], positions[tableIndex + 1]);
+      return new SeekPoints(seekPoint, nextSeekPoint);
+    }
+  }
+
+  @Override
+  public long getTimeUs(long position) {
+    return timesUs[Util.binarySearchFloor(positions, position, true, true)];
+  }
+
+  @Override
+  public long getDurationUs() {
+    return durationUs;
+  }
+
+  @Override
+  public long getDataEndPosition() {
+    return dataEndPosition;
+  }
+}