Supports seeking for FLAC stream using binary search.

Added FlacBinarySearchSeeker, which supports seeking in a FLAC stream by searching for individual frames within the file using binary search.

Github: #1808.

-------------
Created by MOE: https://github.com/google/moe
MOE_MIGRATED_REVID=196587198

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

@@ -0,0 +1,72 @@
+/*
+ * 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.test.InstrumentationTestCase;
+import com.google.android.exoplayer2.extractor.SeekMap;
+import com.google.android.exoplayer2.testutil.FakeExtractorInput;
+import com.google.android.exoplayer2.testutil.TestUtil;
+import java.io.IOException;
+
+/** Unit test for {@link FlacBinarySearchSeeker}. */
+public final class FlacBinarySearchSeekerTest extends InstrumentationTestCase {
+
+  private static final String NOSEEKTABLE_FLAC = "bear_no_seek.flac";
+  private static final int DURATION_US = 2_741_000;
+
+  @Override
+  protected void setUp() throws Exception {
+    super.setUp();
+    if (!FlacLibrary.isAvailable()) {
+      fail("Flac library not available.");
+    }
+  }
+
+  public void testGetSeekMap_returnsSeekMapWithCorrectDuration()
+      throws IOException, FlacDecoderException, InterruptedException {
+    byte[] data = TestUtil.getByteArray(getInstrumentation().getContext(), NOSEEKTABLE_FLAC);
+
+    FakeExtractorInput input = new FakeExtractorInput.Builder().setData(data).build();
+    FlacDecoderJni decoderJni = new FlacDecoderJni();
+    decoderJni.setData(input);
+
+    FlacBinarySearchSeeker seeker =
+        new FlacBinarySearchSeeker(
+            decoderJni.decodeMetadata(), /* firstFramePosition= */ 0, data.length, decoderJni);
+
+    SeekMap seekMap = seeker.getSeekMap();
+    assertThat(seekMap).isNotNull();
+    assertThat(seekMap.getDurationUs()).isEqualTo(DURATION_US);
+    assertThat(seekMap.isSeekable()).isTrue();
+  }
+
+  public void testSetSeekTargetUs_returnsSeekPending()
+      throws IOException, FlacDecoderException, InterruptedException {
+    byte[] data = TestUtil.getByteArray(getInstrumentation().getContext(), NOSEEKTABLE_FLAC);
+
+    FakeExtractorInput input = new FakeExtractorInput.Builder().setData(data).build();
+    FlacDecoderJni decoderJni = new FlacDecoderJni();
+    decoderJni.setData(input);
+    FlacBinarySearchSeeker seeker =
+        new FlacBinarySearchSeeker(
+            decoderJni.decodeMetadata(), /* firstFramePosition= */ 0, data.length, decoderJni);
+
+    seeker.setSeekTargetUs(/* timeUs= */ 1000);
+    assertThat(seeker.hasPendingSeek()).isTrue();
+  }
+}

extensions/flac/src/main/java/com/google/android/exoplayer2/ext/flac/FlacBinarySearchSeeker.java

@@ -0,0 +1,340 @@
+/*
+ * 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 android.support.annotation.Nullable;
+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.extractor.SeekPoint;
+import com.google.android.exoplayer2.util.Assertions;
+import com.google.android.exoplayer2.util.FlacStreamInfo;
+import com.google.android.exoplayer2.util.Util;
+import java.io.IOException;
+import java.nio.ByteBuffer;
+
+/**
+ * A {@link SeekMap} implementation for FLAC stream using binary search.
+ *
+ * <p>This seeker performs seeking by using binary search within the stream, until it finds the
+ * frame that contains the target sample.
+ */
+/* package */ final class FlacBinarySearchSeeker {
+
+  /**
+   * When seeking within the source, if the offset is smaller than or equal to this value, the seek
+   * operation will be performed using a skip operation. Otherwise, the source will be reloaded at
+   * the new seek position.
+   */
+  private static final long MAX_SKIP_BYTES = 256 * 1024;
+
+  private final FlacStreamInfo streamInfo;
+  private final FlacBinarySearchSeekMap seekMap;
+  private final FlacDecoderJni decoderJni;
+
+  private final long firstFramePosition;
+  private final long inputLength;
+  private final long approxBytesPerFrame;
+
+  private @Nullable SeekOperationParams pendingSeekOperationParams;
+
+  public FlacBinarySearchSeeker(
+      FlacStreamInfo streamInfo,
+      long firstFramePosition,
+      long inputLength,
+      FlacDecoderJni decoderJni) {
+    this.streamInfo = Assertions.checkNotNull(streamInfo);
+    this.decoderJni = Assertions.checkNotNull(decoderJni);
+    this.firstFramePosition = firstFramePosition;
+    this.inputLength = inputLength;
+    this.approxBytesPerFrame = streamInfo.getApproxBytesPerFrame();
+
+    pendingSeekOperationParams = null;
+    seekMap =
+        new FlacBinarySearchSeekMap(
+            streamInfo,
+            firstFramePosition,
+            inputLength,
+            streamInfo.durationUs(),
+            approxBytesPerFrame);
+  }
+
+  /** Returns the seek map for the wrapped FLAC stream. */
+  public SeekMap getSeekMap() {
+    return seekMap;
+  }
+
+  /** Sets the target time in microseconds within the stream to seek to. */
+  public void setSeekTargetUs(long timeUs) {
+    if (pendingSeekOperationParams != null && pendingSeekOperationParams.seekTimeUs == timeUs) {
+      return;
+    }
+
+    pendingSeekOperationParams =
+        new SeekOperationParams(
+            timeUs,
+            streamInfo.getSampleIndex(timeUs),
+            /* floorSample= */ 0,
+            /* ceilingSample= */ streamInfo.totalSamples,
+            /* floorPosition= */ firstFramePosition,
+            /* ceilingPosition= */ inputLength,
+            approxBytesPerFrame);
+  }
+
+  /** Returns whether the last operation set by {@link #setSeekTargetUs(long)} is still pending. */
+  public boolean hasPendingSeek() {
+    return pendingSeekOperationParams != null;
+  }
+
+  /**
+   * Continues to handle the pending seek operation. Returns one of the {@code RESULT_} values from
+   * {@link Extractor}.
+   *
+   * @param input The {@link ExtractorInput} from which data should be read.
+   * @param seekPositionHolder If {@link Extractor#RESULT_SEEK} is returned, this holder is updated
+   *     to hold the position of the required seek.
+   * @param outputBuffer If {@link Extractor#RESULT_CONTINUE} is returned, this byte buffer maybe
+   *     updated to hold the extracted frame that contains the target sample. The caller needs to
+   *     check the byte buffer limit to see if an extracted frame is available.
+   * @return One of the {@code RESULT_} values defined in {@link Extractor}.
+   * @throws IOException If an error occurred reading from the input.
+   * @throws InterruptedException If the thread was interrupted.
+   */
+  public int handlePendingSeek(
+      ExtractorInput input, PositionHolder seekPositionHolder, ByteBuffer outputBuffer)
+      throws InterruptedException, IOException {
+    outputBuffer.position(0);
+    outputBuffer.limit(0);
+    while (true) {
+      long floorPosition = pendingSeekOperationParams.floorPosition;
+      long ceilingPosition = pendingSeekOperationParams.ceilingPosition;
+      long searchPosition = pendingSeekOperationParams.nextSearchPosition;
+
+      // streamInfo may not contain minFrameSize, in which case this value will be 0.
+      int minFrameSize = Math.max(1, streamInfo.minFrameSize);
+      if (floorPosition + minFrameSize >= ceilingPosition) {
+        // The seeking range is too small for more than 1 frame, so we can just continue from
+        // the floor position.
+        pendingSeekOperationParams = null;
+        decoderJni.reset(floorPosition);
+        return seekToPosition(input, floorPosition, seekPositionHolder);
+      }
+
+      if (!skipInputUntilPosition(input, searchPosition)) {
+        return seekToPosition(input, searchPosition, seekPositionHolder);
+      }
+
+      decoderJni.reset(searchPosition);
+      try {
+        decoderJni.decodeSampleWithBacktrackPosition(
+            outputBuffer, /* retryPosition= */ searchPosition);
+      } catch (FlacDecoderJni.FlacFrameDecodeException e) {
+        // For some reasons, the extractor can't find a frame mid-stream.
+        // Stop the seeking and let it re-try playing at the last search position.
+        pendingSeekOperationParams = null;
+        throw new IOException("Cannot read frame at position " + searchPosition, e);
+      }
+      if (outputBuffer.limit() == 0) {
+        return Extractor.RESULT_END_OF_INPUT;
+      }
+
+      long lastFrameSampleIndex = decoderJni.getLastFrameFirstSampleIndex();
+      long nextFrameSampleIndex = decoderJni.getNextFrameFirstSampleIndex();
+      long nextFrameSamplePosition = decoderJni.getDecodePosition();
+
+      boolean targetSampleInLastFrame =
+          lastFrameSampleIndex <= pendingSeekOperationParams.targetSample
+              && nextFrameSampleIndex > pendingSeekOperationParams.targetSample;
+
+      if (targetSampleInLastFrame) {
+        pendingSeekOperationParams = null;
+        return Extractor.RESULT_CONTINUE;
+      }
+
+      if (nextFrameSampleIndex <= pendingSeekOperationParams.targetSample) {
+        pendingSeekOperationParams.updateSeekFloor(nextFrameSampleIndex, nextFrameSamplePosition);
+      } else {
+        pendingSeekOperationParams.updateSeekCeiling(lastFrameSampleIndex, searchPosition);
+      }
+    }
+  }
+
+  private boolean skipInputUntilPosition(ExtractorInput input, long position)
+      throws IOException, InterruptedException {
+    long bytesToSkip = position - input.getPosition();
+    if (bytesToSkip >= 0 && bytesToSkip <= MAX_SKIP_BYTES) {
+      input.skipFully((int) bytesToSkip);
+      return true;
+    }
+    return false;
+  }
+
+  private int seekToPosition(
+      ExtractorInput input, long position, PositionHolder seekPositionHolder) {
+    if (position == input.getPosition()) {
+      return Extractor.RESULT_CONTINUE;
+    } else {
+      seekPositionHolder.position = position;
+      return Extractor.RESULT_SEEK;
+    }
+  }
+
+  /**
+   * Contains parameters for a pending seek operation by {@link FlacBinarySearchSeeker}.
+   *
+   * <p>This class holds parameters for a binary-search for the {@code targetSample} in the range
+   * [floorPosition, ceilingPosition).
+   */
+  private static final class SeekOperationParams {
+    private final long seekTimeUs;
+    private final long targetSample;
+    private final long approxBytesPerFrame;
+    private long floorSample;
+    private long ceilingSample;
+    private long floorPosition;
+    private long ceilingPosition;
+    private long nextSearchPosition;
+
+    private SeekOperationParams(
+        long seekTimeUs,
+        long targetSample,
+        long floorSample,
+        long ceilingSample,
+        long floorPosition,
+        long ceilingPosition,
+        long approxBytesPerFrame) {
+      this.seekTimeUs = seekTimeUs;
+      this.floorSample = floorSample;
+      this.ceilingSample = ceilingSample;
+      this.floorPosition = floorPosition;
+      this.ceilingPosition = ceilingPosition;
+      this.targetSample = targetSample;
+      this.approxBytesPerFrame = approxBytesPerFrame;
+      updateNextSearchPosition();
+    }
+
+    /** Updates the floor constraints (inclusive) of the seek operation. */
+    private void updateSeekFloor(long floorSample, long floorPosition) {
+      this.floorSample = floorSample;
+      this.floorPosition = floorPosition;
+      updateNextSearchPosition();
+    }
+
+    /** Updates the ceiling constraints (exclusive) of the seek operation. */
+    private void updateSeekCeiling(long ceilingSample, long ceilingPosition) {
+      this.ceilingSample = ceilingSample;
+      this.ceilingPosition = ceilingPosition;
+      updateNextSearchPosition();
+    }
+
+    private void updateNextSearchPosition() {
+      this.nextSearchPosition =
+          getNextSearchPosition(
+              targetSample,
+              floorSample,
+              ceilingSample,
+              floorPosition,
+              ceilingPosition,
+              approxBytesPerFrame);
+    }
+
+    /**
+     * Returns the next position in FLAC stream to search for target sample, given [floorPosition,
+     * ceilingPosition).
+     */
+    private static long getNextSearchPosition(
+        long targetSample,
+        long floorSample,
+        long ceilingSample,
+        long floorPosition,
+        long ceilingPosition,
+        long approxBytesPerFrame) {
+      if (floorPosition + 1 >= ceilingPosition || floorSample + 1 >= ceilingSample) {
+        return floorPosition;
+      }
+      long samplesToSkip = targetSample - floorSample;
+      long estimatedBytesPerSample =
+          Math.max(1, (ceilingPosition - floorPosition) / (ceilingSample - floorSample));
+      // In the stream, the samples are accessed in a group of frame. Given a stream position, the
+      // seeker will be able to find the first frame following that position.
+      // Hence, if our target sample is in the middle of a frame, and our estimate position is
+      // correct, or very near the actual sample position, the seeker will keep accessing the next
+      // frame, rather than the frame that contains the target sample.
+      // Moreover, it's better to under-estimate rather than over-estimate, because the extractor
+      // input can skip forward easily, but cannot rewind easily (it may require a new connection
+      // to be made).
+      // Therefore, we should reduce the estimated position by some amount, so it will converge to
+      // the correct frame earlier.
+      long bytesToSkip = samplesToSkip * estimatedBytesPerSample;
+      long confidenceInterval = bytesToSkip / 20;
+
+      long estimatedFramePosition = floorPosition + bytesToSkip - (approxBytesPerFrame - 1);
+      long estimatedPosition = estimatedFramePosition - confidenceInterval;
+
+      return Util.constrainValue(estimatedPosition, floorPosition, ceilingPosition - 1);
+    }
+  }
+
+  /**
+   * A {@link SeekMap} implementation that returns the estimated byte location from {@link
+   * SeekOperationParams#getNextSearchPosition(long, long, long, long, long, long)} for each {@link
+   * #getSeekPoints(long)} query.
+   */
+  private static final class FlacBinarySearchSeekMap implements SeekMap {
+    private final FlacStreamInfo streamInfo;
+    private final long firstFramePosition;
+    private final long inputLength;
+    private final long approxBytesPerFrame;
+    private final long durationUs;
+
+    private FlacBinarySearchSeekMap(
+        FlacStreamInfo streamInfo,
+        long firstFramePosition,
+        long inputLength,
+        long durationUs,
+        long approxBytesPerFrame) {
+      this.streamInfo = streamInfo;
+      this.firstFramePosition = firstFramePosition;
+      this.inputLength = inputLength;
+      this.approxBytesPerFrame = approxBytesPerFrame;
+      this.durationUs = durationUs;
+    }
+
+    @Override
+    public boolean isSeekable() {
+      return true;
+    }
+
+    @Override
+    public SeekPoints getSeekPoints(long timeUs) {
+      long nextSearchPosition =
+          SeekOperationParams.getNextSearchPosition(
+              streamInfo.getSampleIndex(timeUs),
+              /* floorSample= */ 0,
+              /* ceilingSample= */ streamInfo.totalSamples,
+              /* floorPosition= */ firstFramePosition,
+              /* ceilingPosition= */ inputLength,
+              approxBytesPerFrame);
+      return new SeekPoints(new SeekPoint(timeUs, nextSearchPosition));
+    }
+
+    @Override
+    public long getDurationUs() {
+      return durationUs;
+    }
+  }
+}

extensions/flac/src/main/java/com/google/android/exoplayer2/ext/flac/FlacDecoder.java

@@ -92,18 +92,14 @@ import java.util.List;
     }
     decoderJni.setData(inputBuffer.data);
     ByteBuffer outputData = outputBuffer.init(inputBuffer.timeUs, maxOutputBufferSize);
-    int result;
     try {
-      result = decoderJni.decodeSample(outputData);
+      decoderJni.decodeSample(outputData);
+    } catch (FlacDecoderJni.FlacFrameDecodeException e) {
+      return new FlacDecoderException("Frame decoding failed", e);
     } catch (IOException | InterruptedException e) {
       // Never happens.
       throw new IllegalStateException(e);
     }
-    if (result < 0) {
-      return new FlacDecoderException("Frame decoding failed");
-    }
-    outputData.position(0);
-    outputData.limit(result);
     return null;
   }
 

extensions/flac/src/main/java/com/google/android/exoplayer2/ext/flac/FlacDecoderJni.java

@@ -26,6 +26,17 @@ import java.nio.ByteBuffer;
  */
 /* package */ final class FlacDecoderJni {
 
+  /** Exception to be thrown if {@link #decodeSample(ByteBuffer)} fails to decode a frame. */
+  public static final class FlacFrameDecodeException extends Exception {
+
+    public final int errorCode;
+
+    public FlacFrameDecodeException(String message, int errorCode) {
+      super(message);
+      this.errorCode = errorCode;
+    }
+  }
+
   private static final int TEMP_BUFFER_SIZE = 8192; // The same buffer size which libflac has
 
   private final long nativeDecoderContext;
@@ -116,14 +127,50 @@ import java.nio.ByteBuffer;
     return byteCount;
   }
 
+  /** Decodes and consumes the StreamInfo section from the FLAC stream. */
   public FlacStreamInfo decodeMetadata() throws IOException, InterruptedException {
     return flacDecodeMetadata(nativeDecoderContext);
   }
 
-  public int decodeSample(ByteBuffer output) throws IOException, InterruptedException {
-    return output.isDirect()
-        ? flacDecodeToBuffer(nativeDecoderContext, output)
-        : flacDecodeToArray(nativeDecoderContext, output.array());
+  /**
+   * Decodes and consumes the next frame from the FLAC stream into the given byte buffer. If any IO
+   * error occurs, resets the stream and input to the given {@code retryPosition}.
+   *
+   * @param output The byte buffer to hold the decoded frame.
+   * @param retryPosition If any error happens, the input will be rewound to {@code retryPosition}.
+   */
+  public void decodeSampleWithBacktrackPosition(ByteBuffer output, long retryPosition)
+      throws InterruptedException, IOException, FlacFrameDecodeException {
+    try {
+      decodeSample(output);
+    } catch (IOException e) {
+      if (retryPosition >= 0) {
+        reset(retryPosition);
+        if (extractorInput != null) {
+          extractorInput.setRetryPosition(retryPosition, e);
+        }
+      }
+      throw e;
+    }
+  }
+
+  /** Decodes and consumes the next sample from the FLAC stream into the given byte buffer. */
+  public void decodeSample(ByteBuffer output)
+      throws IOException, InterruptedException, FlacFrameDecodeException {
+    output.clear();
+    int frameSize =
+        output.isDirect()
+            ? flacDecodeToBuffer(nativeDecoderContext, output)
+            : flacDecodeToArray(nativeDecoderContext, output.array());
+    if (frameSize < 0) {
+      if (!isDecoderAtEndOfInput()) {
+        throw new FlacFrameDecodeException("Cannot decode FLAC frame", frameSize);
+      }
+      // The decoder has read to EOI. Return a 0-size frame to indicate the EOI.
+      output.limit(0);
+    } else {
+      output.limit(frameSize);
+    }
   }
 
   /**
@@ -133,8 +180,19 @@ import java.nio.ByteBuffer;
     return flacGetDecodePosition(nativeDecoderContext);
   }
 
-  public long getLastSampleTimestamp() {
-    return flacGetLastTimestamp(nativeDecoderContext);
+  /** Returns the timestamp for the first sample in the last decoded frame. */
+  public long getLastFrameTimestamp() {
+    return flacGetLastFrameTimestamp(nativeDecoderContext);
+  }
+
+  /** Returns the first sample index of the last extracted frame. */
+  public long getLastFrameFirstSampleIndex() {
+    return flacGetLastFrameFirstSampleIndex(nativeDecoderContext);
+  }
+
+  /** Returns the first sample index of the frame to be extracted next. */
+  public long getNextFrameFirstSampleIndex() {
+    return flacGetNextFrameFirstSampleIndex(nativeDecoderContext);
   }
 
   /**
@@ -153,6 +211,11 @@ import java.nio.ByteBuffer;
     return flacGetStateString(nativeDecoderContext);
   }
 
+  /** Returns whether the decoder has read to the end of the input. */
+  public boolean isDecoderAtEndOfInput() {
+    return flacIsDecoderAtEndOfStream(nativeDecoderContext);
+  }
+
   public void flush() {
     flacFlush(nativeDecoderContext);
   }
@@ -181,18 +244,34 @@ import java.nio.ByteBuffer;
   }
 
   private native long flacInit();
+
   private native FlacStreamInfo flacDecodeMetadata(long context)
       throws IOException, InterruptedException;
+
   private native int flacDecodeToBuffer(long context, ByteBuffer outputBuffer)
       throws IOException, InterruptedException;
+
   private native int flacDecodeToArray(long context, byte[] outputArray)
       throws IOException, InterruptedException;
+
   private native long flacGetDecodePosition(long context);
-  private native long flacGetLastTimestamp(long context);
+
+  private native long flacGetLastFrameTimestamp(long context);
+
+  private native long flacGetLastFrameFirstSampleIndex(long context);
+
+  private native long flacGetNextFrameFirstSampleIndex(long context);
+
   private native long flacGetSeekPosition(long context, long timeUs);
+
   private native String flacGetStateString(long context);
+
+  private native boolean flacIsDecoderAtEndOfStream(long context);
+
   private native void flacFlush(long context);
+
   private native void flacReset(long context, long newPosition);
+
   private native void flacRelease(long context);
 
 }

extensions/flac/src/main/java/com/google/android/exoplayer2/ext/flac/FlacExtractor.java

@@ -179,24 +179,20 @@ public final class FlacExtractor implements Extractor {
       outputByteBuffer = ByteBuffer.wrap(outputBuffer.data);
     }
 
-    outputBuffer.reset();
     long lastDecodePosition = decoderJni.getDecodePosition();
-    int size;
     try {
-      size = decoderJni.decodeSample(outputByteBuffer);
-    } catch (IOException e) {
-      if (lastDecodePosition >= 0) {
-        decoderJni.reset(lastDecodePosition);
-        input.setRetryPosition(lastDecodePosition, e);
-      }
-      throw e;
+      decoderJni.decodeSampleWithBacktrackPosition(outputByteBuffer, lastDecodePosition);
+    } catch (FlacDecoderJni.FlacFrameDecodeException e) {
+      throw new IOException("Cannot read frame at position " + lastDecodePosition, e);
     }
-    if (size <= 0) {
+    int outputSize = outputByteBuffer.limit();
+    if (outputSize == 0) {
       return RESULT_END_OF_INPUT;
     }
-    trackOutput.sampleData(outputBuffer, size);
-    trackOutput.sampleMetadata(decoderJni.getLastSampleTimestamp(), C.BUFFER_FLAG_KEY_FRAME, size,
-        0, null);
+    outputBuffer.setPosition(0);
+    trackOutput.sampleData(outputBuffer, outputSize);
+    trackOutput.sampleMetadata(
+        decoderJni.getLastFrameTimestamp(), C.BUFFER_FLAG_KEY_FRAME, outputSize, 0, null);
 
     return decoderJni.isEndOfData() ? RESULT_END_OF_INPUT : RESULT_CONTINUE;
   }

extensions/flac/src/main/jni/flac_jni.cc

@@ -133,9 +133,19 @@ DECODER_FUNC(jlong, flacGetDecodePosition, jlong jContext) {
   return context->parser->getDecodePosition();
 }
 
-DECODER_FUNC(jlong, flacGetLastTimestamp, jlong jContext) {
+DECODER_FUNC(jlong, flacGetLastFrameTimestamp, jlong jContext) {
   Context *context = reinterpret_cast<Context *>(jContext);
-  return context->parser->getLastTimestamp();
+  return context->parser->getLastFrameTimestamp();
+}
+
+DECODER_FUNC(jlong, flacGetLastFrameFirstSampleIndex, jlong jContext) {
+  Context *context = reinterpret_cast<Context *>(jContext);
+  return context->parser->getLastFrameFirstSampleIndex();
+}
+
+DECODER_FUNC(jlong, flacGetNextFrameFirstSampleIndex, jlong jContext) {
+  Context *context = reinterpret_cast<Context *>(jContext);
+  return context->parser->getNextFrameFirstSampleIndex();
 }
 
 DECODER_FUNC(jlong, flacGetSeekPosition, jlong jContext, jlong timeUs) {
@@ -149,6 +159,11 @@ DECODER_FUNC(jstring, flacGetStateString, jlong jContext) {
   return env->NewStringUTF(str);
 }
 
+DECODER_FUNC(jboolean, flacIsDecoderAtEndOfStream, jlong jContext) {
+  Context *context = reinterpret_cast<Context *>(jContext);
+  return context->parser->isDecoderAtEndOfStream();
+}
+
 DECODER_FUNC(void, flacFlush, jlong jContext) {
   Context *context = reinterpret_cast<Context *>(jContext);
   context->parser->flush();

extensions/flac/src/main/jni/include/flac_parser.h

@@ -44,10 +44,18 @@ class FLACParser {
     return mStreamInfo;
   }
 
-  int64_t getLastTimestamp() const {
+  int64_t getLastFrameTimestamp() const {
     return (1000000LL * mWriteHeader.number.sample_number) / getSampleRate();
   }
 
+  int64_t getLastFrameFirstSampleIndex() const {
+    return mWriteHeader.number.sample_number;
+  }
+
+  int64_t getNextFrameFirstSampleIndex() const {
+    return mWriteHeader.number.sample_number + mWriteHeader.blocksize;
+  }
+
   bool decodeMetadata();
   size_t readBuffer(void *output, size_t output_size);
 
@@ -83,6 +91,11 @@ class FLACParser {
     return FLAC__stream_decoder_get_resolved_state_string(mDecoder);
   }
 
+  bool isDecoderAtEndOfStream() const {
+    return FLAC__stream_decoder_get_state(mDecoder) ==
+           FLAC__STREAM_DECODER_END_OF_STREAM;
+  }
+
  private:
   DataSource *mDataSource;
 

library/core/src/main/java/com/google/android/exoplayer2/util/FlacStreamInfo.java

@@ -15,6 +15,8 @@
  */
 package com.google.android.exoplayer2.util;
 
+import com.google.android.exoplayer2.C;
+
 /**
  * Holder for FLAC stream info.
  */
@@ -52,8 +54,29 @@ public final class FlacStreamInfo {
     // Remaining 16 bytes is md5 value
   }
 
-  public FlacStreamInfo(int minBlockSize, int maxBlockSize, int minFrameSize, int maxFrameSize,
-      int sampleRate, int channels, int bitsPerSample, long totalSamples) {
+  /**
+   * Constructs a FlacStreamInfo given the parameters.
+   *
+   * @param minBlockSize Minimum block size of the FLAC stream.
+   * @param maxBlockSize Maximum block size of the FLAC stream.
+   * @param minFrameSize Minimum frame size of the FLAC stream.
+   * @param maxFrameSize Maximum frame size of the FLAC stream.
+   * @param sampleRate Sample rate of the FLAC stream.
+   * @param channels Number of channels of the FLAC stream.
+   * @param bitsPerSample Number of bits per sample of the FLAC stream.
+   * @param totalSamples Total samples of the FLAC stream.
+   * @see <a href="https://xiph.org/flac/format.html#metadata_block_streaminfo">FLAC format
+   *     METADATA_BLOCK_STREAMINFO</a>
+   */
+  public FlacStreamInfo(
+      int minBlockSize,
+      int maxBlockSize,
+      int minFrameSize,
+      int maxFrameSize,
+      int sampleRate,
+      int channels,
+      int bitsPerSample,
+      long totalSamples) {
     this.minBlockSize = minBlockSize;
     this.maxBlockSize = maxBlockSize;
     this.minFrameSize = minFrameSize;
@@ -64,16 +87,43 @@ public final class FlacStreamInfo {
     this.totalSamples = totalSamples;
   }
 
+  /** Returns the maximum size for a decoded frame from the FLAC stream. */
   public int maxDecodedFrameSize() {
     return maxBlockSize * channels * (bitsPerSample / 8);
   }
 
+  /** Returns the bit-rate of the FLAC stream. */
   public int bitRate() {
     return bitsPerSample * sampleRate;
   }
 
+  /** Returns the duration of the FLAC stream in microseconds. */
   public long durationUs() {
     return (totalSamples * 1000000L) / sampleRate;
   }
 
+  /**
+   * Returns the sample index for the sample at given position.
+   *
+   * @param timeUs Time position in microseconds in the FLAC stream.
+   * @return The sample index for the sample at given position.
+   */
+  public long getSampleIndex(long timeUs) {
+    long sampleIndex = (timeUs * sampleRate) / C.MICROS_PER_SECOND;
+    return Util.constrainValue(sampleIndex, 0, totalSamples - 1);
+  }
+
+  /** Returns the approximate number of bytes per frame for the current FLAC stream. */
+  public long getApproxBytesPerFrame() {
+    long approxBytesPerFrame;
+    if (maxFrameSize > 0) {
+      approxBytesPerFrame = ((long) maxFrameSize + minFrameSize) / 2 + 1;
+    } else {
+      // Uses the stream's block-size if it's a known fixed block-size stream, otherwise uses the
+      // default value for FLAC block-size, which is 4096.
+      long blockSize = (minBlockSize == maxBlockSize && minBlockSize > 0) ? minBlockSize : 4096;
+      approxBytesPerFrame = (blockSize * channels * bitsPerSample) / 8 + 64;
+    }
+    return approxBytesPerFrame;
+  }
 }