content: /*
   * 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.extractor.ts;
  
  import com.google.android.exoplayer2.C;
  import com.google.android.exoplayer2.util.ParsableByteArray;
  
  /** Utilities method for extracting MPEG-TS streams. */
  public final class TsUtil {
  
    /**
     * Returns whether a TS packet starts at {@code searchPosition} according to the MPEG-TS
     * synchronization recommendations.
     *
     * <p>ISO/IEC 13818-1:2015 Annex G recommends that 5 sync bytes emulating the start of 5
     * consecutive TS packets should never occur as part of the TS packets' contents. So, this method
     * returns true when {@code data} contains a sync byte at {@code searchPosition}, and said sync
     * byte is also one of five consecutive sync bytes separated from each other by the size of a TS
     * packet.
     *
     * @param data The array holding the data to search in.
     * @param start The first valid position in {@code data} from which a sync byte can be read.
     * @param limit The first invalid position in {@code data}, after which no data should be read.
     * @param searchPosition The position to check for a TS packet start.
     * @return Whether a TS packet starts at {@code searchPosition}.
     */
    public static boolean isStartOfTsPacket(byte[] data, int start, int limit, int searchPosition) {
      int consecutiveSyncByteCount = 0;
      for (int i = -4; i <= 4; i++) {
        int currentPosition = searchPosition + i * TsExtractor.TS_PACKET_SIZE;
        if (currentPosition < start
            || currentPosition >= limit
            || data[currentPosition] != TsExtractor.TS_SYNC_BYTE) {
          consecutiveSyncByteCount = 0;
        } else if (++consecutiveSyncByteCount == 5) {
          return true;
        }
      }
      return false;
    }
  
    /**
     * Returns the position of the first TS_SYNC_BYTE within the range [startPosition, limitPosition)
     * from the provided data array, or returns limitPosition if sync byte could not be found.
     */
    public static int findSyncBytePosition(byte[] data, int startPosition, int limitPosition) {
      int position = startPosition;
      while (position < limitPosition && data[position] != TsExtractor.TS_SYNC_BYTE) {
        position++;
      }
      return position;
    }
  
    /**
     * Returns the PCR value read from a given TS packet.
     *
     * @param packetBuffer The buffer that holds the packet.
     * @param startOfPacket The starting position of the packet in the buffer.
     * @param pcrPid The PID for valid packets that contain PCR values.
     * @return The PCR value read from the packet, if its PID is equal to {@code pcrPid} and it
     *     contains a valid PCR value. Returns {@link C#TIME_UNSET} otherwise.
     */
    public static long readPcrFromPacket(
        ParsableByteArray packetBuffer, int startOfPacket, int pcrPid) {
      packetBuffer.setPosition(startOfPacket);
      if (packetBuffer.bytesLeft() < 5) {
        // Header = 4 bytes, adaptationFieldLength = 1 byte.
        return C.TIME_UNSET;
      }
      // Note: See ISO/IEC 13818-1, section 2.4.3.2 for details of the header format.
      int tsPacketHeader = packetBuffer.readInt();
      if ((tsPacketHeader & 0x800000) != 0) {
        // transport_error_indicator != 0 means there are uncorrectable errors in this packet.
        return C.TIME_UNSET;
      }
      int pid = (tsPacketHeader & 0x1FFF00) >> 8;
      if (pid != pcrPid) {
        return C.TIME_UNSET;
      }
      boolean adaptationFieldExists = (tsPacketHeader & 0x20) != 0;
      if (!adaptationFieldExists) {
        return C.TIME_UNSET;
      }
  
      int adaptationFieldLength = packetBuffer.readUnsignedByte();
      if (adaptationFieldLength >= 7 && packetBuffer.bytesLeft() >= 7) {
        int flags = packetBuffer.readUnsignedByte();
        boolean pcrFlagSet = (flags & 0x10) == 0x10;
        if (pcrFlagSet) {
          byte[] pcrBytes = new byte[6];
          packetBuffer.readBytes(pcrBytes, /* offset= */ 0, pcrBytes.length);
          return readPcrValueFromPcrBytes(pcrBytes);
        }
      }
      return C.TIME_UNSET;
    }
  
    /**
     * Returns the value of PCR base - first 33 bits in big endian order from the PCR bytes.
     *
     * <p>We ignore PCR Ext, because it's too small to have any significance.
     */
    private static long readPcrValueFromPcrBytes(byte[] pcrBytes) {
      return (pcrBytes[0] & 0xFFL) << 25
          | (pcrBytes[1] & 0xFFL) << 17
          | (pcrBytes[2] & 0xFFL) << 9
          | (pcrBytes[3] & 0xFFL) << 1
          | (pcrBytes[4] & 0xFFL) >> 7;
    }
  
    private TsUtil() {
      // Prevent instantiation.
    }
  }
  