Supports seeking for FLAC files without a SEEKTABLE.

Currently, ExoPlayer only supports seeking for FLAC files with a SEEKTABLE.
This CL adds support seeking for cases when the FLAC files do not have a
SEEKTABLE by searching for individual frames within the file using binary
search.

Github: #1088.

-------------
Created by MOE: https://github.com/google/moe
MOE_MIGRATED_REVID=196816398

RELEASENOTES.md

@@ -11,8 +11,11 @@
     ([#2843](https://github.com/google/ExoPlayer/issues/2843)).
 * Fix crash when switching surface on Moto E(4)
   ([#4134](https://github.com/google/ExoPlayer/issues/4134)).
-* Audio: Fix extraction of PCM in MP4/MOV
-  ([#4228](https://github.com/google/ExoPlayer/issues/4228)).
+* Audio:
+  * Fix extraction of PCM in MP4/MOV
+    ([#4228](https://github.com/google/ExoPlayer/issues/4228)).
+  * FLAC: Supports seeking for FLAC files without SEEKTABLE
+    ([#1808](https://github.com/google/ExoPlayer/issues/1808)).
 * HLS:
   * Fix playback of livestreams with EXT-X-PROGRAM-DATE-TIME tags
     ([#4239](https://github.com/google/ExoPlayer/issues/4239)).

extensions/flac/src/androidTest/java/com/google/android/exoplayer2/ext/flac/FlacExtractorSeekTest.java

@@ -0,0 +1,281 @@
+/*
+ * Copyright (C) 2018 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.exoplayer2.ext.flac;
+
+import static com.google.common.truth.Truth.assertThat;
+
+import android.content.Context;
+import android.net.Uri;
+import android.support.annotation.Nullable;
+import android.test.InstrumentationTestCase;
+import com.google.android.exoplayer2.C;
+import com.google.android.exoplayer2.extractor.DefaultExtractorInput;
+import com.google.android.exoplayer2.extractor.Extractor;
+import com.google.android.exoplayer2.extractor.ExtractorInput;
+import com.google.android.exoplayer2.extractor.PositionHolder;
+import com.google.android.exoplayer2.extractor.SeekMap;
+import com.google.android.exoplayer2.testutil.FakeExtractorInput;
+import com.google.android.exoplayer2.testutil.FakeExtractorOutput;
+import com.google.android.exoplayer2.testutil.FakeTrackOutput;
+import com.google.android.exoplayer2.testutil.TestUtil;
+import com.google.android.exoplayer2.upstream.DataSpec;
+import com.google.android.exoplayer2.upstream.DefaultDataSource;
+import com.google.android.exoplayer2.upstream.DefaultDataSourceFactory;
+import com.google.android.exoplayer2.util.Util;
+import java.io.IOException;
+import java.util.List;
+import java.util.Random;
+
+/** Seeking tests for {@link FlacExtractor} when the FLAC stream does not have a SEEKTABLE. */
+public final class FlacExtractorSeekTest extends InstrumentationTestCase {
+
+  private static final String NO_SEEKTABLE_FLAC = "bear_no_seek.flac";
+  private static final int DURATION_US = 2_741_000;
+  private static final Uri FILE_URI = Uri.parse("file:///android_asset/" + NO_SEEKTABLE_FLAC);
+  private static final Random RANDOM = new Random(1234L);
+
+  private FakeExtractorOutput expectedOutput;
+  private FakeTrackOutput expectedTrackOutput;
+
+  private DefaultDataSource dataSource;
+  private PositionHolder positionHolder;
+  private long totalInputLength;
+
+  @Override
+  protected void setUp() throws Exception {
+    super.setUp();
+    if (!FlacLibrary.isAvailable()) {
+      fail("Flac library not available.");
+    }
+    expectedOutput = new FakeExtractorOutput();
+    extractAllSamplesFromFileToExpectedOutput(getInstrumentation().getContext(), NO_SEEKTABLE_FLAC);
+    expectedTrackOutput = expectedOutput.trackOutputs.get(0);
+
+    dataSource =
+        new DefaultDataSourceFactory(getInstrumentation().getContext(), "UserAgent")
+            .createDataSource();
+    totalInputLength = readInputLength();
+    positionHolder = new PositionHolder();
+  }
+
+  public void testFlacExtractorReads_nonSeekTableFile_returnSeekableSeekMap()
+      throws IOException, InterruptedException {
+    FlacExtractor extractor = new FlacExtractor();
+
+    SeekMap seekMap = extractSeekMap(extractor, new FakeExtractorOutput());
+
+    assertThat(seekMap).isNotNull();
+    assertThat(seekMap.getDurationUs()).isEqualTo(DURATION_US);
+    assertThat(seekMap.isSeekable()).isTrue();
+  }
+
+  public void testHandlePendingSeek_handlesSeekingToPositionInFile_extractsCorrectFrame()
+      throws IOException, InterruptedException {
+    FlacExtractor extractor = new FlacExtractor();
+
+    FakeExtractorOutput extractorOutput = new FakeExtractorOutput();
+    SeekMap seekMap = extractSeekMap(extractor, extractorOutput);
+    FakeTrackOutput trackOutput = extractorOutput.trackOutputs.get(0);
+
+    long targetSeekTimeUs = 987_000;
+    int extractedFrameIndex = seekToTimeUs(extractor, seekMap, targetSeekTimeUs, trackOutput);
+
+    assertThat(extractedFrameIndex).isNotEqualTo(-1);
+    assertFirstFrameAfterSeekContainTargetSeekTime(
+        trackOutput, targetSeekTimeUs, extractedFrameIndex);
+  }
+
+  public void testHandlePendingSeek_handlesSeekToEoF_extractsLastFrame()
+      throws IOException, InterruptedException {
+    FlacExtractor extractor = new FlacExtractor();
+
+    FakeExtractorOutput extractorOutput = new FakeExtractorOutput();
+    SeekMap seekMap = extractSeekMap(extractor, extractorOutput);
+    FakeTrackOutput trackOutput = extractorOutput.trackOutputs.get(0);
+
+    long targetSeekTimeUs = seekMap.getDurationUs();
+
+    int extractedFrameIndex = seekToTimeUs(extractor, seekMap, targetSeekTimeUs, trackOutput);
+
+    assertThat(extractedFrameIndex).isNotEqualTo(-1);
+    assertFirstFrameAfterSeekContainTargetSeekTime(
+        trackOutput, targetSeekTimeUs, extractedFrameIndex);
+  }
+
+  public void testHandlePendingSeek_handlesSeekingBackward_extractsCorrectFrame()
+      throws IOException, InterruptedException {
+    FlacExtractor extractor = new FlacExtractor();
+
+    FakeExtractorOutput extractorOutput = new FakeExtractorOutput();
+    SeekMap seekMap = extractSeekMap(extractor, extractorOutput);
+    FakeTrackOutput trackOutput = extractorOutput.trackOutputs.get(0);
+
+    long firstSeekTimeUs = 987_000;
+    seekToTimeUs(extractor, seekMap, firstSeekTimeUs, trackOutput);
+
+    long targetSeekTimeUs = 0;
+    int extractedFrameIndex = seekToTimeUs(extractor, seekMap, targetSeekTimeUs, trackOutput);
+
+    assertThat(extractedFrameIndex).isNotEqualTo(-1);
+    assertFirstFrameAfterSeekContainTargetSeekTime(
+        trackOutput, targetSeekTimeUs, extractedFrameIndex);
+  }
+
+  public void testHandlePendingSeek_handlesSeekingForward_extractsCorrectFrame()
+      throws IOException, InterruptedException {
+    FlacExtractor extractor = new FlacExtractor();
+
+    FakeExtractorOutput extractorOutput = new FakeExtractorOutput();
+    SeekMap seekMap = extractSeekMap(extractor, extractorOutput);
+    FakeTrackOutput trackOutput = extractorOutput.trackOutputs.get(0);
+
+    long firstSeekTimeUs = 987_000;
+    seekToTimeUs(extractor, seekMap, firstSeekTimeUs, trackOutput);
+
+    long targetSeekTimeUs = 1_234_000;
+    int extractedFrameIndex = seekToTimeUs(extractor, seekMap, targetSeekTimeUs, trackOutput);
+
+    assertThat(extractedFrameIndex).isNotEqualTo(-1);
+    assertFirstFrameAfterSeekContainTargetSeekTime(
+        trackOutput, targetSeekTimeUs, extractedFrameIndex);
+  }
+
+  public void testHandlePendingSeek_handlesRandomSeeks_extractsCorrectFrame()
+      throws IOException, InterruptedException {
+    FlacExtractor extractor = new FlacExtractor();
+
+    FakeExtractorOutput extractorOutput = new FakeExtractorOutput();
+    SeekMap seekMap = extractSeekMap(extractor, extractorOutput);
+    FakeTrackOutput trackOutput = extractorOutput.trackOutputs.get(0);
+
+    long numSeek = 100;
+    for (long i = 0; i < numSeek; i++) {
+      long targetSeekTimeUs = RANDOM.nextInt(DURATION_US + 1);
+      int extractedFrameIndex = seekToTimeUs(extractor, seekMap, targetSeekTimeUs, trackOutput);
+
+      assertThat(extractedFrameIndex).isNotEqualTo(-1);
+      assertFirstFrameAfterSeekContainTargetSeekTime(
+          trackOutput, targetSeekTimeUs, extractedFrameIndex);
+    }
+  }
+
+  // Internal methods
+
+  private long readInputLength() throws IOException {
+    DataSpec dataSpec = new DataSpec(FILE_URI, 0, C.LENGTH_UNSET, null);
+    long totalInputLength = dataSource.open(dataSpec);
+    Util.closeQuietly(dataSource);
+    return totalInputLength;
+  }
+
+  /**
+   * Seeks to the given seek time and keeps reading from input until we can extract at least one
+   * frame from the seek position, or until end-of-input is reached.
+   *
+   * @return The index of the first extracted frame written to the given {@code trackOutput} after
+   *     the seek is completed, or -1 if the seek is completed without any extracted frame.
+   */
+  private int seekToTimeUs(
+      FlacExtractor flacExtractor, SeekMap seekMap, long seekTimeUs, FakeTrackOutput trackOutput)
+      throws IOException, InterruptedException {
+    int numSampleBeforeSeek = trackOutput.getSampleCount();
+    SeekMap.SeekPoints seekPoints = seekMap.getSeekPoints(seekTimeUs);
+
+    long initialSeekLoadPosition = seekPoints.first.position;
+    flacExtractor.seek(initialSeekLoadPosition, seekTimeUs);
+
+    positionHolder.position = C.POSITION_UNSET;
+    ExtractorInput extractorInput = getExtractorInputFromPosition(initialSeekLoadPosition);
+    int extractorReadResult = Extractor.RESULT_CONTINUE;
+    while (true) {
+      try {
+        // Keep reading until we can read at least one frame after seek
+        while (extractorReadResult == Extractor.RESULT_CONTINUE
+            && trackOutput.getSampleCount() == numSampleBeforeSeek) {
+          extractorReadResult = flacExtractor.read(extractorInput, positionHolder);
+        }
+      } finally {
+        Util.closeQuietly(dataSource);
+      }
+
+      if (extractorReadResult == Extractor.RESULT_SEEK) {
+        extractorInput = getExtractorInputFromPosition(positionHolder.position);
+        extractorReadResult = Extractor.RESULT_CONTINUE;
+      } else if (extractorReadResult == Extractor.RESULT_END_OF_INPUT) {
+        return -1;
+      } else if (trackOutput.getSampleCount() > numSampleBeforeSeek) {
+        // First index after seek = num sample before seek.
+        return numSampleBeforeSeek;
+      }
+    }
+  }
+
+  private @Nullable SeekMap extractSeekMap(FlacExtractor extractor, FakeExtractorOutput output)
+      throws IOException, InterruptedException {
+    try {
+      ExtractorInput input = getExtractorInputFromPosition(0);
+      extractor.init(output);
+      while (output.seekMap == null) {
+        extractor.read(input, positionHolder);
+      }
+    } finally {
+      Util.closeQuietly(dataSource);
+    }
+    return output.seekMap;
+  }
+
+  private void assertFirstFrameAfterSeekContainTargetSeekTime(
+      FakeTrackOutput trackOutput, long seekTimeUs, int firstFrameIndexAfterSeek) {
+    int expectedSampleIndex = findTargetFrameInExpectedOutput(seekTimeUs);
+    // Assert that after seeking, the first sample frame written to output contains the sample
+    // at seek time.
+    trackOutput.assertSample(
+        firstFrameIndexAfterSeek,
+        expectedTrackOutput.getSampleData(expectedSampleIndex),
+        expectedTrackOutput.getSampleTimeUs(expectedSampleIndex),
+        expectedTrackOutput.getSampleFlags(expectedSampleIndex),
+        expectedTrackOutput.getSampleCryptoData(expectedSampleIndex));
+  }
+
+  private int findTargetFrameInExpectedOutput(long seekTimeUs) {
+    List<Long> sampleTimes = expectedTrackOutput.getSampleTimesUs();
+    for (int i = 0; i < sampleTimes.size() - 1; i++) {
+      long currentSampleTime = sampleTimes.get(i);
+      long nextSampleTime = sampleTimes.get(i + 1);
+      if (currentSampleTime <= seekTimeUs && nextSampleTime > seekTimeUs) {
+        return i;
+      }
+    }
+    return sampleTimes.size() - 1;
+  }
+
+  private ExtractorInput getExtractorInputFromPosition(long position) throws IOException {
+    DataSpec dataSpec = new DataSpec(FILE_URI, position, totalInputLength, /* key= */ null);
+    dataSource.open(dataSpec);
+    return new DefaultExtractorInput(dataSource, position, totalInputLength);
+  }
+
+  private void extractAllSamplesFromFileToExpectedOutput(Context context, String fileName)
+      throws IOException, InterruptedException {
+    byte[] data = TestUtil.getByteArray(context, fileName);
+
+    FlacExtractor extractor = new FlacExtractor();
+    extractor.init(expectedOutput);
+    FakeExtractorInput input = new FakeExtractorInput.Builder().setData(data).build();
+
+    while (extractor.read(input, new PositionHolder()) != Extractor.RESULT_END_OF_INPUT) {}
+  }
+}