c= cv2.waitKey(30) & 0xff if c==27: capture.release() break

这段代码是一个按键监听的功能实现。它使用了`cv2.waitKey()`函数来等待用户输入按键，并将返回值与0xff进行与运算。如果用户按下的是ESC键（ASCII码为27），则会释放视频捕获对象（`capture.release()`）并跳出循环（`break`），从而终止程序执行。这样可以实现在按下ESC键时停止视频播放或退出程序的功能。

相关问题

cv2.videocapture

cv2.VideoCapture is a function in the OpenCV library that is used for capturing video from a camera or a video file. It creates a video capture object that can be used to read frames from the video source. The function takes a parameter that specifies the index of the camera or the path of the video file to be opened.

Syntax:

cv2.VideoCapture(index or filename)

Example:

import cv2

# Open the default camera
cap = cv2.VideoCapture(0)

# Check if camera opened successfully
if not cap.isOpened():
    print("Error opening video stream or file")

# Read until video is completed
while cap.isOpened():
    # Capture frame-by-frame
    ret, frame = cap.read()

    if ret:
        # Display the resulting frame
        cv2.imshow('Frame', frame)

        # Press Q on keyboard to exit
        if cv2.waitKey(25) & 0xFF == ord('q'):
            break
    else:
        break

# Release the video capture object and close all windows
cap.release()
cv2.destroyAllWindows()

In this example, the function is used to open the default camera (index 0) and read frames from it. The frames are displayed using the cv2.imshow() function and the loop is exited when the user presses the 'q' key on the keyboard. Finally, the video capture object is released using the cap.release() function and all windows are closed using cv2.destroyAllWindows().

cv2.VideoCapture

cv2.VideoCapture是OpenCV中用于捕获视频的函数。它可以从摄像头、视频文件或网络视频流中获取帧。可以使用该函数来读取视频文件中的帧并进行处理，例如分析视频中的运动、检测和跟踪对象等。

使用cv2.VideoCapture函数时，需要传入一个参数，该参数可以是摄像头设备的编号，也可以是视频文件的路径。例如，如果要从电脑上连接的摄像头获取视频，则可以使用以下代码：

import cv2

cap = cv2.VideoCapture(0)

while(True):
    # Capture frame-by-frame
    ret, frame = cap.read()

    # Display the resulting frame
    cv2.imshow('frame',frame)
    if cv2.waitKey(1) & 0xFF == ord('q'):
        break

# When everything done, release the capture
cap.release()
cv2.destroyAllWindows()

在上面的代码中，我们使用了cv2.VideoCapture(0)来获取摄像头设备的编号为0的摄像头。然后在while循环中，使用cap.read()函数获取每一帧视频，并在窗口中显示出来。在按下“q”键后，释放摄像头并关闭所有窗口。