如何使用处理和UDP接收Tello无人机的视频流

Question

我正在尝试使用SDK documentation中所述的“处理”来接收Tello无人机的视频流：

要通过UDP接收视频流，我尝试使用a script by The Coding Train：

import java.awt.image.*; 
import javax.imageio.*;
import java.net.*;
import java.io.*;


// Port we are receiving.
int port = 11111; 
DatagramSocket ds; 
// A byte array to read into (max size of 65536, could be smaller)
byte[] buffer = new byte[65536]; 

PImage video;

void setup() {
  size(400,300);
  try {
    ds = new DatagramSocket(port);
  } catch (SocketException e) {
    e.printStackTrace();
  } 
  video = createImage(320,240,RGB);
}

 void draw() {
  // checkForImage() is blocking, stay tuned for threaded example!
  checkForImage();

  // Draw the image
  background(0);
  imageMode(CENTER);
  image(video,width/2,height/2);
}

void checkForImage() {
  DatagramPacket p = new DatagramPacket(buffer, buffer.length); 
  try {
    ds.receive(p);
  } catch (IOException e) {
    e.printStackTrace();
  } 
  byte[] data = p.getData();

  println("Received datagram with " + data.length + " bytes." );

  // Read incoming data into a ByteArrayInputStream
  ByteArrayInputStream bais = new ByteArrayInputStream( data );

  // We need to unpack JPG and put it in the PImage video
  video.loadPixels();
  try {
    // Make a BufferedImage out of the incoming bytes
    BufferedImage img = ImageIO.read(bais);
    // Put the pixels into the video PImage
    img.getRGB(0, 0, video.width, video.height, video.pixels, 0, video.width);
  } catch (Exception e) {
    e.printStackTrace();
  }
  // Update the PImage pixels
  video.updatePixels();
}

我在脚本中唯一更改的是变量port，正如SDK文档（见上文）所指定的那样，它应该为11111。

运行脚本时（成功将command和streamon发送到无人机后），我收到消息Received datagram with 65536 bytes.和空指针异常。我发现，显示了Null Pointer Exception，因为下面的代码行返回null：

BufferedImage img = ImageIO.read(bais);

所以最后，我的问题是，为什么这一行代码或更具体地说ImageIO.read(bais)返回null。但是，如果将脚本与Video Sender script of the Coding Train结合使用，则脚本可以正常工作。那么，这是什么问题？