/**
   * Copies the content of the most recently received packet into <tt>data</tt>.
   *
   * @param buffer an optional <tt>Buffer</tt> instance associated with the specified <tt>data</tt>,
   *     <tt>offset</tt> and <tt>length</tt> and provided to the method in case the implementation
   *     would like to provide additional <tt>Buffer</tt> properties such as <tt>flags</tt>
   * @param data the <tt>byte[]</tt> that we'd like to copy the content of the packet to.
   * @param offset the position where we are supposed to start writing in <tt>data</tt>.
   * @param length the number of <tt>byte</tt>s available for writing in <tt>data</tt>.
   * @return the number of bytes read
   * @throws IOException if <tt>length</tt> is less than the size of the packet.
   */
  protected int read(Buffer buffer, byte[] data, int offset, int length) throws IOException {
    if (data == null) throw new NullPointerException("data");

    if (ioError) return -1;

    RawPacket pkt;

    synchronized (pktSyncRoot) {
      pkt = this.pkt;
      this.pkt = null;
    }

    int pktLength;

    if (pkt == null) {
      pktLength = 0;
    } else {
      // By default, pkt will be returned to the pool after it was read.
      boolean poolPkt = true;

      try {
        pktLength = pkt.getLength();
        if (length < pktLength) {
          /*
           * If pkt is still the latest RawPacket made available to
           * reading, reinstate it for the next invocation of read;
           * otherwise, return it to the pool.
           */
          poolPkt = false;
          throw new IOException("Input buffer not big enough for " + pktLength);
        } else {
          byte[] pktBuffer = pkt.getBuffer();

          if (pktBuffer == null) {
            throw new NullPointerException(
                "pkt.buffer null, pkt.length " + pktLength + ", pkt.offset " + pkt.getOffset());
          } else {
            System.arraycopy(pkt.getBuffer(), pkt.getOffset(), data, offset, pktLength);
            if (buffer != null) buffer.setFlags(pkt.getFlags());
          }
        }
      } finally {
        if (!poolPkt) {
          synchronized (pktSyncRoot) {
            if (this.pkt == null) this.pkt = pkt;
            else poolPkt = true;
          }
        }
        if (poolPkt) {
          // Return pkt to the pool because it was successfully read.
          poolRawPacket(pkt);
        }
      }
    }

    return pktLength;
  }
Esempio n. 2
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      public int write(byte[] buffer, int offset, int length, boolean transform) {
        RawPacket pkt = rawPacketArray[0];
        if (pkt == null) pkt = new RawPacket();
        rawPacketArray[0] = pkt;

        byte[] pktBuf = pkt.getBuffer();
        if (pktBuf == null || pktBuf.length < length) {
          pktBuf = new byte[length];
          pkt.setBuffer(pktBuf);
        }
        System.arraycopy(buffer, offset, pktBuf, 0, length);
        pkt.setOffset(0);
        pkt.setLength(length);

        if (transform) {
          PacketTransformer packetTransformer =
              isControlStream ? rtcpPacketTransformer : rtpPacketTransformer;

          if (packetTransformer != null)
            rawPacketArray = packetTransformer.reverseTransform(rawPacketArray);
        }

        SourceTransferHandler transferHandler;
        PushSourceStream pushSourceStream;

        try {
          if (isControlStream) {
            transferHandler = controlTransferHandler;
            pushSourceStream = getControlInputStream();
          } else {
            transferHandler = dataTransferHandler;
            pushSourceStream = getDataInputStream();
          }
        } catch (IOException ioe) {
          throw new UndeclaredThrowableException(ioe);
        }

        for (int i = 0; i < rawPacketArray.length; i++) {
          RawPacket packet = rawPacketArray[i];

          // keep the first element for reuse
          if (i != 0) rawPacketArray[i] = null;

          if (packet != null) {
            if (isControlStream) pendingControlPacket = packet;
            else pendingDataPacket = packet;

            if (transferHandler != null) {
              transferHandler.transferData(pushSourceStream);
            }
          }
        }

        return length;
      }
  /**
   * Encapsulates {@code pkt} in the RTX format, using {@code rtxSsrc} as its SSRC, and transmits it
   * to {@link #channel} by injecting it in the {@code MediaStream}.
   *
   * @param pkt the packet to transmit.
   * @param rtxSsrc the SSRC for the RTX stream.
   * @return {@code true} if the packet was successfully retransmitted, {@code false} otherwise.
   */
  private boolean encapsulateInRtxAndTransmit(RawPacket pkt, long rtxSsrc) {
    byte[] buf = pkt.getBuffer();
    int len = pkt.getLength();
    int off = pkt.getOffset();
    byte[] newBuf = buf;
    if (buf.length < len + 2) {
      // FIXME The byte array newly allocated and assigned to newBuf must
      // be made known to pkt eventually.
      newBuf = new byte[len + 2];
    }

    int osn = pkt.getSequenceNumber();
    int headerLength = pkt.getHeaderLength();
    int payloadLength = len - headerLength;
    System.arraycopy(buf, off, newBuf, 0, headerLength);
    // FIXME If newBuf is actually buf, then we will override the first two
    // bytes of the payload bellow.
    newBuf[headerLength] = (byte) ((osn >> 8) & 0xff);
    newBuf[headerLength + 1] = (byte) (osn & 0xff);
    System.arraycopy(buf, off + headerLength, newBuf, headerLength + 2, payloadLength);
    // FIXME We tried to extend the payload of pkt by two bytes above but
    // we never told pkt that its length has increased by these two bytes.

    MediaStream mediaStream = channel.getStream();
    if (mediaStream != null) {
      pkt.setSSRC((int) rtxSsrc);
      // Only call getNextRtxSequenceNumber() when we're sure we're going
      // to transmit a packet, because it consumes a sequence number.
      pkt.setSequenceNumber(getNextRtxSequenceNumber(rtxSsrc));
      try {
        mediaStream.injectPacket(pkt, /* data */ true, /* after */ null);
      } catch (TransmissionFailedException tfe) {
        logger.warn("Failed to transmit an RTX packet.");
        return false;
      }
    }

    return true;
  }
  /**
   * Encapsulates {@code pkt} in the RTX format, using {@code rtxSsrc} as its SSRC, and transmits it
   * to {@link #channel} by injecting it in the {@code MediaStream}.
   *
   * @param pkt the packet to transmit.
   * @param rtxSsrc the SSRC for the RTX stream.
   * @param after the {@code TransformEngine} in the chain of {@code TransformEngine}s of the
   *     associated {@code MediaStream} after which the injection of {@code pkt} is to begin
   * @return {@code true} if the packet was successfully retransmitted, {@code false} otherwise.
   */
  private boolean encapsulateInRtxAndTransmit(RawPacket pkt, long rtxSsrc, TransformEngine after) {
    byte[] buf = pkt.getBuffer();
    int len = pkt.getLength();
    int off = pkt.getOffset();

    byte[] newBuf = new byte[len + 2];
    RawPacket rtxPkt = new RawPacket(newBuf, 0, len + 2);

    int osn = pkt.getSequenceNumber();
    int headerLength = pkt.getHeaderLength();
    int payloadLength = pkt.getPayloadLength();

    // Copy the header.
    System.arraycopy(buf, off, newBuf, 0, headerLength);

    // Set the OSN field.
    newBuf[headerLength] = (byte) ((osn >> 8) & 0xff);
    newBuf[headerLength + 1] = (byte) (osn & 0xff);

    // Copy the payload.
    System.arraycopy(buf, off + headerLength, newBuf, headerLength + 2, payloadLength);

    MediaStream mediaStream = channel.getStream();
    if (mediaStream != null) {
      rtxPkt.setSSRC((int) rtxSsrc);
      rtxPkt.setPayloadType(rtxPayloadType);
      // Only call getNextRtxSequenceNumber() when we're sure we're going
      // to transmit a packet, because it consumes a sequence number.
      rtxPkt.setSequenceNumber(getNextRtxSequenceNumber(rtxSsrc));
      try {
        mediaStream.injectPacket(rtxPkt, /* data */ true, after);
      } catch (TransmissionFailedException tfe) {
        logger.warn("Failed to transmit an RTX packet.");
        return false;
      }
    }

    return true;
  }
  /**
   * Adds a <tt>DatagramPacketFilter</tt> which allows dropping <tt>DatagramPacket</tt>s before they
   * are converted into <tt>RawPacket</tt>s.
   *
   * @param datagramPacketFilter the <tt>DatagramPacketFilter</tt> which allows dropping
   *     <tt>DatagramPacket</tt>s before they are converted into <tt>RawPacket</tt>s
   */
  public synchronized void addDatagramPacketFilter(DatagramPacketFilter datagramPacketFilter) {
    if (datagramPacketFilter == null) throw new NullPointerException("datagramPacketFilter");

    if (datagramPacketFilters == null) {
      datagramPacketFilters = new DatagramPacketFilter[] {datagramPacketFilter};
    } else {
      final int length = datagramPacketFilters.length;

      for (int i = 0; i < length; i++)
        if (datagramPacketFilter.equals(datagramPacketFilters[i])) return;

      DatagramPacketFilter[] newDatagramPacketFilters = new DatagramPacketFilter[length + 1];

      System.arraycopy(datagramPacketFilters, 0, newDatagramPacketFilters, 0, length);
      newDatagramPacketFilters[length] = datagramPacketFilter;
      datagramPacketFilters = newDatagramPacketFilters;
    }
  }
Esempio n. 6
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      @Override
      public int read(byte[] buffer, int offset, int length) throws IOException {

        RawPacket pendingPacket;
        if (isControlStream) {
          pendingPacket = pendingControlPacket;
        } else {
          pendingPacket = pendingDataPacket;
        }
        int bytesToRead = 0;
        byte[] pendingPacketBuffer = pendingPacket.getBuffer();
        if (pendingPacketBuffer != null) {
          int pendingPacketLength = pendingPacket.getLength();
          bytesToRead = length > pendingPacketLength ? pendingPacketLength : length;
          System.arraycopy(
              pendingPacketBuffer, pendingPacket.getOffset(), buffer, offset, bytesToRead);
        }
        return bytesToRead;
      }
  /**
   * Removes the RTX encapsulation from a packet.
   *
   * @param pkt the packet to remove the RTX encapsulation from.
   * @return the original media packet represented by {@code pkt}, or null if we couldn't
   *     reconstruct the original packet.
   */
  private RawPacket deRtx(RawPacket pkt) {
    boolean success = false;

    if (pkt.getPayloadLength() - pkt.getPaddingSize() < 2) {
      // We need at least 2 bytes to read the OSN field.
      if (logger.isDebugEnabled()) {
        logger.debug("Dropping an incoming RTX packet with padding only: " + pkt);
      }
      return null;
    }

    long mediaSsrc = getPrimarySsrc(pkt);
    if (mediaSsrc != -1) {
      if (rtxAssociatedPayloadType != -1) {
        int osn = pkt.getOriginalSequenceNumber();
        // Remove the RTX header by moving the RTP header two bytes
        // right.
        byte[] buf = pkt.getBuffer();
        int off = pkt.getOffset();
        System.arraycopy(buf, off, buf, off + 2, pkt.getHeaderLength());

        pkt.setOffset(off + 2);
        pkt.setLength(pkt.getLength() - 2);

        pkt.setSSRC((int) mediaSsrc);
        pkt.setSequenceNumber(osn);
        pkt.setPayloadType(rtxAssociatedPayloadType);
        success = true;
      } else {
        logger.warn(
            "RTX packet received, but no APT is defined. Packet "
                + "SSRC "
                + pkt.getSSRCAsLong()
                + ", associated media"
                + " SSRC "
                + mediaSsrc);
      }
    }

    // If we failed to handle the RTX packet, drop it.
    return success ? pkt : null;
  }
  /**
   * Creates a {@code RawPacket} which represents the original packet encapsulated in {@code pkt}
   * using the RTX format.
   *
   * @param pkt the packet from which to extract a media packet.
   * @return the extracted media packet.
   */
  private RawPacket createMediaPacket(RawPacket pkt) {
    RawPacket mediaPacket = null;
    long rtxSsrc = pkt.getSSRC() & 0xffffffffL;

    // We need to know the SSRC paired with rtxSsrc *as seen by the
    // receiver (i.e. this.channel)*. However, we only store SSRCs
    // that endpoints *send* with.
    // We therefore assume that SSRC re-writing has not introduced any
    // new SSRCs and therefor the FID mappings known to the senders
    // also apply to receivers.
    RtpChannel sourceChannel = channel.getContent().findChannelByFidSsrc(rtxSsrc);
    if (sourceChannel != null) {
      long mediaSsrc = sourceChannel.getFidPairedSsrc(rtxSsrc);
      if (mediaSsrc != -1) {
        byte apt = sourceChannel.getRtxAssociatedPayloadType();
        if (apt != -1) {
          mediaPacket = new RawPacket(pkt.getBuffer().clone(), pkt.getOffset(), pkt.getLength());

          // Remove the RTX header by moving the RTP header two bytes
          // right.
          byte[] buf = mediaPacket.getBuffer();
          int off = mediaPacket.getOffset();
          System.arraycopy(buf, off, buf, off + 2, mediaPacket.getHeaderLength());

          mediaPacket.setOffset(off + 2);
          mediaPacket.setLength(pkt.getLength() - 2);

          mediaPacket.setSSRC((int) mediaSsrc);
          mediaPacket.setSequenceNumber(pkt.getOriginalSequenceNumber());
          mediaPacket.setPayloadType(apt);
        }
      }
    }

    return mediaPacket;
  }
  /**
   * Makes <tt>RTCPRRPacket</tt>s using information in FMJ.
   *
   * @param time
   * @return A <tt>Collection</tt> of <tt>RTCPRRPacket</tt>s to inject to the <tt>MediaStream</tt>.
   */
  private Collection<RTCPRRPacket> makeRTCPRRPackets(long time) {
    RTCPReportBlock[] reportBlocks = makeRTCPReportBlocks(time);
    if (reportBlocks == null || reportBlocks.length == 0) {
      return null;
    }

    Collection<RTCPRRPacket> rrPackets = new ArrayList<RTCPRRPacket>();

    // We use the stream's local source ID (SSRC) as the SSRC of packet
    // sender.
    long streamSSRC = getLocalSSRC();

    // Since a maximum of 31 reception report blocks will fit in an SR
    // or RR packet, additional RR packets SHOULD be stacked after the
    // initial SR or RR packet as needed to contain the reception
    // reports for all sources heard during the interval since the last
    // report.
    if (reportBlocks.length > MAX_RTCP_REPORT_BLOCKS) {
      for (int offset = 0; offset < reportBlocks.length; offset += MAX_RTCP_REPORT_BLOCKS) {
        RTCPReportBlock[] blocks =
            (reportBlocks.length - offset < MAX_RTCP_REPORT_BLOCKS)
                ? new RTCPReportBlock[reportBlocks.length - offset]
                : MAX_RTCP_REPORT_BLOCKS_ARRAY;

        System.arraycopy(reportBlocks, offset, blocks, 0, blocks.length);

        RTCPRRPacket rr = new RTCPRRPacket((int) streamSSRC, blocks);
        rrPackets.add(rr);
      }
    } else {
      RTCPRRPacket rr = new RTCPRRPacket((int) streamSSRC, reportBlocks);
      rrPackets.add(rr);
    }

    return rrPackets;
  }
Esempio n. 10
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  /** {@inheritDoc} */
  @Override
  protected int doProcess(Buffer inBuffer, Buffer outBuffer) {
    byte[] inData = (byte[]) inBuffer.getData();
    int inOffset = inBuffer.getOffset();

    if (!VP8PayloadDescriptor.isValid(inData, inOffset)) {
      logger.warn("Invalid RTP/VP8 packet discarded.");
      outBuffer.setDiscard(true);
      return BUFFER_PROCESSED_FAILED; // XXX: FAILED or OK?
    }

    long inSeq = inBuffer.getSequenceNumber();
    long inRtpTimestamp = inBuffer.getRtpTimeStamp();
    int inPictureId = VP8PayloadDescriptor.getPictureId(inData, inOffset);
    boolean inMarker = (inBuffer.getFlags() & Buffer.FLAG_RTP_MARKER) != 0;
    boolean inIsStartOfFrame = VP8PayloadDescriptor.isStartOfFrame(inData, inOffset);
    int inLength = inBuffer.getLength();
    int inPdSize = VP8PayloadDescriptor.getSize(inData, inOffset);
    int inPayloadLength = inLength - inPdSize;

    if (empty && lastSentSeq != -1 && seqNumComparator.compare(inSeq, lastSentSeq) != 1) {
      if (logger.isInfoEnabled()) logger.info("Discarding old packet (while empty) " + inSeq);
      outBuffer.setDiscard(true);
      return BUFFER_PROCESSED_OK;
    }

    if (!empty) {
      // if the incoming packet has a different PictureID or timestamp
      // than those of the current frame, then it belongs to a different
      // frame.
      if ((inPictureId != -1 && pictureId != -1 && inPictureId != pictureId)
          | (timestamp != -1 && inRtpTimestamp != -1 && inRtpTimestamp != timestamp)) {
        if (seqNumComparator.compare(inSeq, firstSeq) != 1) // inSeq <= firstSeq
        {
          // the packet belongs to a previous frame. discard it
          if (logger.isInfoEnabled()) logger.info("Discarding old packet " + inSeq);
          outBuffer.setDiscard(true);
          return BUFFER_PROCESSED_OK;
        } else // inSeq > firstSeq (and also presumably isSeq > lastSeq)
        {
          // the packet belongs to a subsequent frame (to the one
          // currently being held). Drop the current frame.

          if (logger.isInfoEnabled())
            logger.info(
                "Discarding saved packets on arrival of"
                    + " a packet for a subsequent frame: "
                    + inSeq);

          // TODO: this would be the place to complain about the
          // not-well-received PictureID by sending a RTCP SLI or NACK.
          reinit();
        }
      }
    }

    // a whole frame in a single packet. avoid the extra copy to
    // this.data and output it immediately.
    if (empty && inMarker && inIsStartOfFrame) {
      byte[] outData = validateByteArraySize(outBuffer, inPayloadLength, false);
      System.arraycopy(inData, inOffset + inPdSize, outData, 0, inPayloadLength);
      outBuffer.setOffset(0);
      outBuffer.setLength(inPayloadLength);
      outBuffer.setRtpTimeStamp(inBuffer.getRtpTimeStamp());

      if (TRACE) logger.trace("Out PictureID=" + inPictureId);

      lastSentSeq = inSeq;

      return BUFFER_PROCESSED_OK;
    }

    // add to this.data
    Container container = free.poll();
    if (container == null) container = new Container();
    if (container.buf == null || container.buf.length < inPayloadLength)
      container.buf = new byte[inPayloadLength];

    if (data.get(inSeq) != null) {
      if (logger.isInfoEnabled())
        logger.info("(Probable) duplicate packet detected, discarding " + inSeq);
      outBuffer.setDiscard(true);
      return BUFFER_PROCESSED_OK;
    }

    System.arraycopy(inData, inOffset + inPdSize, container.buf, 0, inPayloadLength);
    container.len = inPayloadLength;
    data.put(inSeq, container);

    // update fields
    frameLength += inPayloadLength;
    if (firstSeq == -1 || (seqNumComparator.compare(firstSeq, inSeq) == 1)) firstSeq = inSeq;
    if (lastSeq == -1 || (seqNumComparator.compare(inSeq, lastSeq) == 1)) lastSeq = inSeq;

    if (empty) {
      // the first received packet for the current frame was just added
      empty = false;
      timestamp = inRtpTimestamp;
      pictureId = inPictureId;
    }

    if (inMarker) haveEnd = true;
    if (inIsStartOfFrame) haveStart = true;

    // check if we have a full frame
    if (frameComplete()) {
      byte[] outData = validateByteArraySize(outBuffer, frameLength, false);
      int ptr = 0;
      Container b;
      for (Map.Entry<Long, Container> entry : data.entrySet()) {
        b = entry.getValue();
        System.arraycopy(b.buf, 0, outData, ptr, b.len);
        ptr += b.len;
      }

      outBuffer.setOffset(0);
      outBuffer.setLength(frameLength);
      outBuffer.setRtpTimeStamp(inBuffer.getRtpTimeStamp());

      if (TRACE) logger.trace("Out PictureID=" + inPictureId);
      lastSentSeq = lastSeq;

      // prepare for the next frame
      reinit();

      return BUFFER_PROCESSED_OK;
    } else {
      // frame not complete yet
      outBuffer.setDiscard(true);
      return OUTPUT_BUFFER_NOT_FILLED;
    }
  }
Esempio n. 11
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  /**
   * Initializes a new <tt>SRTPTransformer</tt> instance with a specific (negotiated)
   * <tt>SRTPProtectionProfile</tt> and the keying material specified by a specific
   * <tt>TlsContext</tt>.
   *
   * @param srtpProtectionProfile the (negotiated) <tt>SRTPProtectionProfile</tt> to initialize the
   *     new instance with
   * @param tlsContext the <tt>TlsContext</tt> which represents the keying material
   * @return a new <tt>SRTPTransformer</tt> instance initialized with <tt>srtpProtectionProfile</tt>
   *     and <tt>tlsContext</tt>
   */
  private SinglePacketTransformer initializeSRTPTransformer(
      int srtpProtectionProfile, TlsContext tlsContext) {
    boolean rtcp;

    switch (componentID) {
      case Component.RTCP:
        rtcp = true;
        break;
      case Component.RTP:
        rtcp = false;
        break;
      default:
        throw new IllegalStateException("componentID");
    }

    int cipher_key_length;
    int cipher_salt_length;
    int cipher;
    int auth_function;
    int auth_key_length;
    int RTCP_auth_tag_length, RTP_auth_tag_length;

    switch (srtpProtectionProfile) {
      case SRTPProtectionProfile.SRTP_AES128_CM_HMAC_SHA1_32:
        cipher_key_length = 128 / 8;
        cipher_salt_length = 112 / 8;
        cipher = SRTPPolicy.AESCM_ENCRYPTION;
        auth_function = SRTPPolicy.HMACSHA1_AUTHENTICATION;
        auth_key_length = 160 / 8;
        RTCP_auth_tag_length = 80 / 8;
        RTP_auth_tag_length = 32 / 8;
        break;
      case SRTPProtectionProfile.SRTP_AES128_CM_HMAC_SHA1_80:
        cipher_key_length = 128 / 8;
        cipher_salt_length = 112 / 8;
        cipher = SRTPPolicy.AESCM_ENCRYPTION;
        auth_function = SRTPPolicy.HMACSHA1_AUTHENTICATION;
        auth_key_length = 160 / 8;
        RTCP_auth_tag_length = RTP_auth_tag_length = 80 / 8;
        break;
      case SRTPProtectionProfile.SRTP_NULL_HMAC_SHA1_32:
        cipher_key_length = 0;
        cipher_salt_length = 0;
        cipher = SRTPPolicy.NULL_ENCRYPTION;
        auth_function = SRTPPolicy.HMACSHA1_AUTHENTICATION;
        auth_key_length = 160 / 8;
        RTCP_auth_tag_length = 80 / 8;
        RTP_auth_tag_length = 32 / 8;
        break;
      case SRTPProtectionProfile.SRTP_NULL_HMAC_SHA1_80:
        cipher_key_length = 0;
        cipher_salt_length = 0;
        cipher = SRTPPolicy.NULL_ENCRYPTION;
        auth_function = SRTPPolicy.HMACSHA1_AUTHENTICATION;
        auth_key_length = 160 / 8;
        RTCP_auth_tag_length = RTP_auth_tag_length = 80 / 8;
        break;
      default:
        throw new IllegalArgumentException("srtpProtectionProfile");
    }

    byte[] keyingMaterial =
        tlsContext.exportKeyingMaterial(
            ExporterLabel.dtls_srtp, null, 2 * (cipher_key_length + cipher_salt_length));
    byte[] client_write_SRTP_master_key = new byte[cipher_key_length];
    byte[] server_write_SRTP_master_key = new byte[cipher_key_length];
    byte[] client_write_SRTP_master_salt = new byte[cipher_salt_length];
    byte[] server_write_SRTP_master_salt = new byte[cipher_salt_length];
    byte[][] keyingMaterialValues = {
      client_write_SRTP_master_key,
      server_write_SRTP_master_key,
      client_write_SRTP_master_salt,
      server_write_SRTP_master_salt
    };

    for (int i = 0, keyingMaterialOffset = 0; i < keyingMaterialValues.length; i++) {
      byte[] keyingMaterialValue = keyingMaterialValues[i];

      System.arraycopy(
          keyingMaterial, keyingMaterialOffset, keyingMaterialValue, 0, keyingMaterialValue.length);
      keyingMaterialOffset += keyingMaterialValue.length;
    }

    SRTPPolicy srtcpPolicy =
        new SRTPPolicy(
            cipher,
            cipher_key_length,
            auth_function,
            auth_key_length,
            RTCP_auth_tag_length,
            cipher_salt_length);
    SRTPPolicy srtpPolicy =
        new SRTPPolicy(
            cipher,
            cipher_key_length,
            auth_function,
            auth_key_length,
            RTP_auth_tag_length,
            cipher_salt_length);
    SRTPContextFactory clientSRTPContextFactory =
        new SRTPContextFactory(
            /* sender */ tlsContext instanceof TlsClientContext,
            client_write_SRTP_master_key,
            client_write_SRTP_master_salt,
            srtpPolicy,
            srtcpPolicy);
    SRTPContextFactory serverSRTPContextFactory =
        new SRTPContextFactory(
            /* sender */ tlsContext instanceof TlsServerContext,
            server_write_SRTP_master_key,
            server_write_SRTP_master_salt,
            srtpPolicy,
            srtcpPolicy);
    SRTPContextFactory forwardSRTPContextFactory;
    SRTPContextFactory reverseSRTPContextFactory;

    if (tlsContext instanceof TlsClientContext) {
      forwardSRTPContextFactory = clientSRTPContextFactory;
      reverseSRTPContextFactory = serverSRTPContextFactory;
    } else if (tlsContext instanceof TlsServerContext) {
      forwardSRTPContextFactory = serverSRTPContextFactory;
      reverseSRTPContextFactory = clientSRTPContextFactory;
    } else {
      throw new IllegalArgumentException("tlsContext");
    }

    SinglePacketTransformer srtpTransformer;

    if (rtcp) {
      srtpTransformer = new SRTCPTransformer(forwardSRTPContextFactory, reverseSRTPContextFactory);
    } else {
      srtpTransformer = new SRTPTransformer(forwardSRTPContextFactory, reverseSRTPContextFactory);
    }
    return srtpTransformer;
  }