content: /*
   * 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.exoplayer2.extractor.mp3;
  
  import com.google.android.exoplayer2.C;
  import com.google.android.exoplayer2.extractor.MpegAudioHeader;
  import com.google.android.exoplayer2.extractor.SeekPoint;
  import com.google.android.exoplayer2.util.Util;
  
  /**
   * MP3 seeker that doesn't rely on metadata and seeks assuming the source has a constant bitrate.
   */
  /* package */ final class ConstantBitrateSeeker implements Mp3Extractor.Seeker {
  
    private static final int BITS_PER_BYTE = 8;
  
    private final long firstFramePosition;
    private final int frameSize;
    private final long dataSize;
    private final int bitrate;
    private final long durationUs;
  
    /**
     * @param inputLength The length of the stream in bytes, or {@link C#LENGTH_UNSET} if unknown.
     * @param firstFramePosition The position of the first frame in the stream.
     * @param mpegAudioHeader The MPEG audio header associated with the first frame.
     */
    public ConstantBitrateSeeker(long inputLength, long firstFramePosition,
        MpegAudioHeader mpegAudioHeader) {
      this.firstFramePosition = firstFramePosition;
      this.frameSize = mpegAudioHeader.frameSize;
      this.bitrate = mpegAudioHeader.bitrate;
      if (inputLength == C.LENGTH_UNSET) {
        dataSize = C.LENGTH_UNSET;
        durationUs = C.TIME_UNSET;
      } else {
        dataSize = inputLength - firstFramePosition;
        durationUs = getTimeUs(inputLength);
      }
    }
  
    @Override
    public boolean isSeekable() {
      return dataSize != C.LENGTH_UNSET;
    }
  
    @Override
    public SeekPoints getSeekPoints(long timeUs) {
      if (dataSize == C.LENGTH_UNSET) {
        return new SeekPoints(new SeekPoint(0, firstFramePosition));
      }
      long positionOffset = (timeUs * bitrate) / (C.MICROS_PER_SECOND * BITS_PER_BYTE);
      // Constrain to nearest preceding frame offset.
      positionOffset = (positionOffset / frameSize) * frameSize;
      positionOffset = Util.constrainValue(positionOffset, 0, dataSize - frameSize);
      long seekPosition = firstFramePosition + positionOffset;
      long seekTimeUs = getTimeUs(seekPosition);
      SeekPoint seekPoint = new SeekPoint(seekTimeUs, seekPosition);
      if (seekTimeUs >= timeUs || positionOffset == dataSize - frameSize) {
        return new SeekPoints(seekPoint);
      } else {
        long secondSeekPosition = seekPosition + frameSize;
        long secondSeekTimeUs = getTimeUs(secondSeekPosition);
        SeekPoint secondSeekPoint = new SeekPoint(secondSeekTimeUs, secondSeekPosition);
        return new SeekPoints(seekPoint, secondSeekPoint);
      }
    }
  
    @Override
    public long getTimeUs(long position) {
      return (Math.max(0, position - firstFramePosition) * C.MICROS_PER_SECOND * BITS_PER_BYTE)
          / bitrate;
    }
  
    @Override
    public long getDurationUs() {
      return durationUs;
    }
  
  }
  