用python写一个能获取USB设备视频流的小工具

在Python中，我们可以利用`pyudev`库来检测USB设备，并结合一些图像处理库如`opencv-python`来获取视频流。以下是一个简单的示例，展示如何编写一个小工具来扫描USB摄像头并打开其视频流：

import cv2
import pyudev

def find_usb_cameras():
    context = pyudev.Context()
    monitor = pyudev.Monitor.from_netlink(context)
    monitor.filter_by('video4linux2')
    
    for device in iter(monitor.poll, None):
        if device.action == 'add':
            try:
                vid_pid = (device.device_info['ID_VID'], device.device_info['ID_PID'])
                camera_device = '/dev/video{}'.format(device.device_node.split('/')[-1])
                
                # 尝试打开摄像头
                cap = cv2.VideoCapture(camera_device)
                if cap.isOpened():
                    print("Found USB Camera with ID: {}, Device Path: {}".format(vid_pid, camera_device))
                    yield cap
            except Exception as e:
                print("Error accessing {} - {}".format(device.device_node, str(e)))

# 使用这个函数打开第一个找到的USB摄像头
for cap in find_usb_cameras():
    while True:
        ret, frame = cap.read()  # 获取一帧
        if not ret:
            break
        cv2.imshow('USB Camera Stream', frame)  # 显示帧
        key = cv2.waitKey(1)
        if key & 0xFF == ord('q'):  # 按 q 键退出
            break
    cap.release()
    cv2.destroyAllWindows()