/**
   * Capture a part of the desktop screen using <tt>java.awt.Robot</tt>.
   *
   * @param x x position to start capture
   * @param y y position to start capture
   * @param width capture width
   * @param height capture height
   * @return <tt>BufferedImage</tt> of a part of the desktop screen or null if Robot problem
   */
  public BufferedImage captureScreen(int x, int y, int width, int height) {
    BufferedImage img = null;
    Rectangle rect = null;

    if (robot == null) {
      /* Robot has not been created so abort */
      return null;
    }

    if (logger.isInfoEnabled()) logger.info("Begin capture: " + System.nanoTime());
    rect = new Rectangle(x, y, width, height);
    img = robot.createScreenCapture(rect);
    if (logger.isInfoEnabled()) logger.info("End capture: " + System.nanoTime());

    return img;
  }
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  /**
   * Blocks and reads into a <tt>Buffer</tt> from this <tt>PullBufferStream</tt>.
   *
   * @param buffer the <tt>Buffer</tt> this <tt>PullBufferStream</tt> is to read into
   * @throws IOException if an I/O error occurs while this <tt>PullBufferStream</tt> reads into the
   *     specified <tt>Buffer</tt>
   * @see AbstractVideoPullBufferStream#doRead(Buffer)
   */
  @Override
  protected void doRead(Buffer buffer) throws IOException {
    /*
     * Determine the Format in which we're expected to output. We cannot
     * rely on the Format always being specified in the Buffer because it is
     * not its responsibility, the DataSource of this ImageStream knows the
     * output Format.
     */
    Format format = buffer.getFormat();

    if (format == null) {
      format = getFormat();
      if (format != null) buffer.setFormat(format);
    }

    if (format instanceof AVFrameFormat) {
      Object o = buffer.getData();
      AVFrame frame;

      if (o instanceof AVFrame) frame = (AVFrame) o;
      else {
        frame = new AVFrame();
        buffer.setData(frame);
      }

      AVFrameFormat avFrameFormat = (AVFrameFormat) format;
      Dimension size = avFrameFormat.getSize();
      ByteBuffer data = readScreenNative(size);

      if (data != null) {
        if (frame.avpicture_fill(data, avFrameFormat) < 0) {
          data.free();
          throw new IOException("avpicture_fill");
        }
      } else {
        /*
         * This can happen when we disconnect a monitor from computer
         * before or during grabbing.
         */
        throw new IOException("Failed to grab screen.");
      }
    } else {
      byte[] bytes = (byte[]) buffer.getData();
      Dimension size = ((VideoFormat) format).getSize();

      bytes = readScreen(bytes, size);

      buffer.setData(bytes);
      buffer.setOffset(0);
      buffer.setLength(bytes.length);
    }

    buffer.setHeader(null);
    buffer.setTimeStamp(System.nanoTime());
    buffer.setSequenceNumber(seqNo);
    buffer.setFlags(Buffer.FLAG_SYSTEM_TIME | Buffer.FLAG_LIVE_DATA);
    seqNo++;
  }