/**
   * Tries to find an SSRC paired with {@code ssrc} in an FID group in one of the channels from
   * {@link #channel}'s {@code Content}. Returns -1 on failure.
   *
   * @param pkt the {@code RawPacket} that holds the RTP packet for which to find a paired SSRC.
   * @return An SSRC paired with {@code ssrc} in an FID group, or -1.
   */
  private long getRtxSsrc(RawPacket pkt) {
    StreamRTPManager receiveRTPManager =
        channel.getStream().getRTPTranslator().findStreamRTPManagerByReceiveSSRC(pkt.getSSRC());

    MediaStreamTrackReceiver receiver = null;
    if (receiveRTPManager != null) {
      MediaStream receiveStream = receiveRTPManager.getMediaStream();
      if (receiveStream != null) {
        receiver = receiveStream.getMediaStreamTrackReceiver();
      }
    }

    if (receiver == null) {
      return -1;
    }

    RTPEncoding encoding = receiver.resolveRTPEncoding(pkt);
    if (encoding == null) {
      logger.warn(
          "encoding_not_found"
              + ",stream_hash="
              + channel.getStream().hashCode()
              + " ssrc="
              + pkt.getSSRCAsLong());
      return -1;
    }

    return encoding.getRTXSSRC();
  }
  /**
   * Returns the SSRC paired with <tt>ssrc</tt> in an FID source-group, if any. If none is found,
   * returns -1.
   *
   * @return the SSRC paired with <tt>ssrc</tt> in an FID source-group, if any. If none is found,
   *     returns -1.
   */
  private long getPrimarySsrc(RawPacket pkt) {
    MediaStreamTrackReceiver receiver = channel.getStream().getMediaStreamTrackReceiver();

    if (receiver == null) {
      if (logger.isDebugEnabled()) {
        logger.debug("Dropping an incoming RTX packet from an unknown source.");
      }
      return -1;
    }

    RTPEncoding encoding = receiver.resolveRTPEncoding(pkt);
    if (encoding == null) {
      if (logger.isDebugEnabled()) {
        logger.debug("Dropping an incoming RTX packet from an unknown source.");
      }
      return -1;
    }

    return encoding.getPrimarySSRC();
  }