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.text.webvtt;
  
  import androidx.annotation.Nullable;
  import com.google.android.exoplayer2.text.Cue;
  import com.google.android.exoplayer2.text.SimpleSubtitleDecoder;
  import com.google.android.exoplayer2.text.Subtitle;
  import com.google.android.exoplayer2.text.SubtitleDecoderException;
  import com.google.android.exoplayer2.util.ParsableByteArray;
  import com.google.android.exoplayer2.util.Util;
  import java.util.ArrayList;
  import java.util.Collections;
  import java.util.List;
  
  /** A {@link SimpleSubtitleDecoder} for Webvtt embedded in a Mp4 container file. */
  @SuppressWarnings("ConstantField")
  public final class Mp4WebvttDecoder extends SimpleSubtitleDecoder {
  
    private static final int BOX_HEADER_SIZE = 8;
  
    @SuppressWarnings("ConstantCaseForConstants")
    private static final int TYPE_payl = 0x7061796c;
  
    @SuppressWarnings("ConstantCaseForConstants")
    private static final int TYPE_sttg = 0x73747467;
  
    @SuppressWarnings("ConstantCaseForConstants")
    private static final int TYPE_vttc = 0x76747463;
  
    private final ParsableByteArray sampleData;
  
    public Mp4WebvttDecoder() {
      super("Mp4WebvttDecoder");
      sampleData = new ParsableByteArray();
    }
  
    @Override
    protected Subtitle decode(byte[] data, int length, boolean reset)
        throws SubtitleDecoderException {
      // Webvtt in Mp4 samples have boxes inside of them, so we have to do a traditional box parsing:
      // first 4 bytes size and then 4 bytes type.
      sampleData.reset(data, length);
      List<Cue> resultingCueList = new ArrayList<>();
      while (sampleData.bytesLeft() > 0) {
        if (sampleData.bytesLeft() < BOX_HEADER_SIZE) {
          throw new SubtitleDecoderException("Incomplete Mp4Webvtt Top Level box header found.");
        }
        int boxSize = sampleData.readInt();
        int boxType = sampleData.readInt();
        if (boxType == TYPE_vttc) {
          resultingCueList.add(parseVttCueBox(sampleData, boxSize - BOX_HEADER_SIZE));
        } else {
          // Peers of the VTTCueBox are still not supported and are skipped.
          sampleData.skipBytes(boxSize - BOX_HEADER_SIZE);
        }
      }
      return new Mp4WebvttSubtitle(resultingCueList);
    }
  
    private static Cue parseVttCueBox(ParsableByteArray sampleData, int remainingCueBoxBytes)
        throws SubtitleDecoderException {
      @Nullable Cue.Builder cueBuilder = null;
      @Nullable CharSequence cueText = null;
      while (remainingCueBoxBytes > 0) {
        if (remainingCueBoxBytes < BOX_HEADER_SIZE) {
          throw new SubtitleDecoderException("Incomplete vtt cue box header found.");
        }
        int boxSize = sampleData.readInt();
        int boxType = sampleData.readInt();
        remainingCueBoxBytes -= BOX_HEADER_SIZE;
        int payloadLength = boxSize - BOX_HEADER_SIZE;
        String boxPayload =
            Util.fromUtf8Bytes(sampleData.getData(), sampleData.getPosition(), payloadLength);
        sampleData.skipBytes(payloadLength);
        remainingCueBoxBytes -= payloadLength;
        if (boxType == TYPE_sttg) {
          cueBuilder = WebvttCueParser.parseCueSettingsList(boxPayload);
        } else if (boxType == TYPE_payl) {
          cueText =
              WebvttCueParser.parseCueText(
                  /* id= */ null, boxPayload.trim(), /* styles= */ Collections.emptyList());
        } else {
          // Other VTTCueBox children are still not supported and are ignored.
        }
      }
      if (cueText == null) {
        cueText = "";
      }
      return cueBuilder != null
          ? cueBuilder.setText(cueText).build()
          : WebvttCueParser.newCueForText(cueText);
    }
  }
  