content: /*
   * Copyright 2022 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.source.rtsp.reader;
  
  import static com.google.android.exoplayer2.source.rtsp.reader.RtpReaderUtils.toSampleTimeUs;
  import static com.google.android.exoplayer2.util.Assertions.checkNotNull;
  import static com.google.android.exoplayer2.util.Assertions.checkState;
  import static com.google.android.exoplayer2.util.Assertions.checkStateNotNull;
  
  import com.google.android.exoplayer2.C;
  import com.google.android.exoplayer2.extractor.ExtractorOutput;
  import com.google.android.exoplayer2.extractor.TrackOutput;
  import com.google.android.exoplayer2.source.rtsp.RtpPacket;
  import com.google.android.exoplayer2.source.rtsp.RtpPayloadFormat;
  import com.google.android.exoplayer2.util.Log;
  import com.google.android.exoplayer2.util.ParsableByteArray;
  import com.google.android.exoplayer2.util.Util;
  import org.checkerframework.checker.nullness.qual.MonotonicNonNull;
  
  /**
   * Parses a H263 byte stream carried on RTP packets, and extracts H263 frames as defined in RFC4629.
   */
  /* package */ final class RtpH263Reader implements RtpPayloadReader {
    private static final String TAG = "RtpH263Reader";
  
    private static final int MEDIA_CLOCK_FREQUENCY = 90_000;
  
    /** I-frame VOP unit type. */
    private static final int I_VOP = 0;
  
    /** Picture start code, P=1, V=0, PLEN=0. Refer to RFC4629 Section 6.1. */
    private static final int PICTURE_START_CODE = 128;
  
    private final RtpPayloadFormat payloadFormat;
  
    private @MonotonicNonNull TrackOutput trackOutput;
  
    /**
     * First received RTP timestamp. All RTP timestamps are dimension-less, the time base is defined
     * by {@link #MEDIA_CLOCK_FREQUENCY}.
     */
    private long firstReceivedTimestamp;
  
    /** The combined size of a sample that is fragmented into multiple RTP packets. */
    private int fragmentedSampleSizeBytes;
  
    private int previousSequenceNumber;
  
    private int width;
    private int height;
    private boolean isKeyFrame;
    private boolean isOutputFormatSet;
    private long startTimeOffsetUs;
    private long fragmentedSampleTimeUs;
    /**
     * Whether the first packet of a H263 frame is received, it mark the start of a H263 partition. A
     * H263 frame can be split into multiple RTP packets.
     */
    private boolean gotFirstPacketOfH263Frame;
  
    /** Creates an instance. */
    public RtpH263Reader(RtpPayloadFormat payloadFormat) {
      this.payloadFormat = payloadFormat;
      firstReceivedTimestamp = C.TIME_UNSET;
      previousSequenceNumber = C.INDEX_UNSET;
    }
  
    @Override
    public void createTracks(ExtractorOutput extractorOutput, int trackId) {
      trackOutput = extractorOutput.track(trackId, C.TRACK_TYPE_VIDEO);
      trackOutput.format(payloadFormat.format);
    }
  
    @Override
    public void onReceivingFirstPacket(long timestamp, int sequenceNumber) {
      checkState(firstReceivedTimestamp == C.TIME_UNSET);
      firstReceivedTimestamp = timestamp;
    }
  
    @Override
    public void consume(
        ParsableByteArray data, long timestamp, int sequenceNumber, boolean rtpMarker) {
      checkStateNotNull(trackOutput);
  
      // H263 Header Payload Header, RFC4629 Section 5.1.
      //    0                   1
      //    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5
      //    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      //    |   RR    |P|V|   PLEN    |PEBIT|
      //    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      int currentPosition = data.getPosition();
      int header = data.readUnsignedShort();
      boolean pBitIsSet = (header & 0x400) > 0;
  
      // Check if optional V (Video Redundancy Coding), PLEN or PEBIT is present, RFC4629 Section 5.1.
      if ((header & 0x200) != 0 || (header & 0x1F8) != 0 || (header & 0x7) != 0) {
        Log.w(
            TAG,
            "Dropping packet: video reduncancy coding is not supported, packet header VRC, or PLEN or"
                + " PEBIT is non-zero");
        return;
      }
  
      if (pBitIsSet) {
        if (gotFirstPacketOfH263Frame && fragmentedSampleSizeBytes > 0) {
          // Received new H263 fragment, output data of previous fragment to decoder.
          outputSampleMetadataForFragmentedPackets();
        }
        gotFirstPacketOfH263Frame = true;
  
        int payloadStartCode = data.peekUnsignedByte() & 0xFC;
        // Packets that begin with a Picture Start Code(100000). Refer RFC4629 Section 6.1.
        if (payloadStartCode < PICTURE_START_CODE) {
          Log.w(TAG, "Picture start Code (PSC) missing, dropping packet.");
          return;
        }
        // Setting first two bytes of the start code. Refer RFC4629 Section 6.1.1.
        data.getData()[currentPosition] = 0;
        data.getData()[currentPosition + 1] = 0;
        data.setPosition(currentPosition);
      } else if (gotFirstPacketOfH263Frame) {
        // Check that this packet is in the sequence of the previous packet.
        int expectedSequenceNumber = RtpPacket.getNextSequenceNumber(previousSequenceNumber);
        if (sequenceNumber < expectedSequenceNumber) {
          Log.w(
              TAG,
              Util.formatInvariant(
                  "Received RTP packet with unexpected sequence number. Expected: %d; received: %d."
                      + " Dropping packet.",
                  expectedSequenceNumber, sequenceNumber));
          return;
        }
      } else {
        Log.w(
            TAG,
            "First payload octet of the H263 packet is not the beginning of a new H263 partition,"
                + " Dropping current packet.");
        return;
      }
  
      if (fragmentedSampleSizeBytes == 0) {
        parseVopHeader(data, isOutputFormatSet);
        if (!isOutputFormatSet && isKeyFrame) {
          if (width != payloadFormat.format.width || height != payloadFormat.format.height) {
            trackOutput.format(
                payloadFormat.format.buildUpon().setWidth(width).setHeight(height).build());
          }
          isOutputFormatSet = true;
        }
      }
      int fragmentSize = data.bytesLeft();
      // Write the video sample.
      trackOutput.sampleData(data, fragmentSize);
      fragmentedSampleSizeBytes += fragmentSize;
      fragmentedSampleTimeUs =
          toSampleTimeUs(startTimeOffsetUs, timestamp, firstReceivedTimestamp, MEDIA_CLOCK_FREQUENCY);
  
      if (rtpMarker) {
        outputSampleMetadataForFragmentedPackets();
      }
      previousSequenceNumber = sequenceNumber;
    }
  
    @Override
    public void seek(long nextRtpTimestamp, long timeUs) {
      firstReceivedTimestamp = nextRtpTimestamp;
      fragmentedSampleSizeBytes = 0;
      startTimeOffsetUs = timeUs;
    }
  
    /**
     * Parses and set VOP Coding type and resolution. The {@linkplain ParsableByteArray#getPosition()
     * position} is preserved.
     */
    private void parseVopHeader(ParsableByteArray data, boolean gotResolution) {
      // Picture Segment Packets (RFC4629 Section 6.1).
      // Search for SHORT_VIDEO_START_MARKER (0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1 0 0 0 0 0).
      int currentPosition = data.getPosition();
  
      /*
       * Parse short video header.
       *
       * These values are taken from <a
       * href=https://cs.android.com/android/platform/superproject/+/master:frameworks/av/media/codecs/m4v_h263/dec/src/mp4def.h;l=115
       * >Android's software H263 decoder</a>.
       */
      long shortVideoHeader = data.readUnsignedInt();
      if (((shortVideoHeader >> 10) & 0x3F) == 0x20) {
        int header = data.peekUnsignedByte();
        int vopType = ((header >> 1) & 0x1);
        if (!gotResolution && vopType == I_VOP) {
          /*
           * Parse resolution from source format.
           *
           * These values are taken from <a
           * href=https://cs.android.com/android/platform/superproject/+/master:frameworks/av/media/codecs/m4v_h263/dec/src/vop.cpp;l=1126
           * >Android's software H263 decoder</a>.
           */
          int sourceFormat = ((header >> 2) & 0x07);
          if (sourceFormat == 1) {
            width = 128;
            height = 96;
          } else {
            width = 176 << (sourceFormat - 2);
            height = 144 << (sourceFormat - 2);
          }
        }
        data.setPosition(currentPosition);
        isKeyFrame = vopType == I_VOP;
        return;
      }
      data.setPosition(currentPosition);
      isKeyFrame = false;
    }
  
    /**
     * Outputs sample metadata of the received fragmented packets.
     *
     * <p>Call this method only after receiving an end of a H263 partition.
     */
    private void outputSampleMetadataForFragmentedPackets() {
      checkNotNull(trackOutput)
          .sampleMetadata(
              fragmentedSampleTimeUs,
              isKeyFrame ? C.BUFFER_FLAG_KEY_FRAME : 0,
              fragmentedSampleSizeBytes,
              /* offset= */ 0,
              /* cryptoData= */ null);
      fragmentedSampleSizeBytes = 0;
      fragmentedSampleTimeUs = C.TIME_UNSET;
      isKeyFrame = false;
      gotFirstPacketOfH263Frame = false;
    }
  }
  