我在python中使用opencv库。我打开了一个现有的视频文件，并编写了一个小脚本，允许我在视频的任何地方画一个矩形。问题是：我想在视频的第一帧上画一个矩形，然后把它留在那里为我标记一个感兴趣的区域。在

我正在使用cv2.imshow(winname, frame)显示我的视频。因为它每秒以非常高的帧速率运行/显示视频(我不想改变它，因为我的视频很长)，当我开始绘制矩形时，已经显示了许多帧。在

因为我认为这可能有帮助，下面是我目前为止的代码：

进口cv2#mouse callback function#

def draw_rectangle(event, x, y, flags, param):

global pt1, pt2, topLeft_clicked, bottomRight_clicked

#mouse click

if event == cv2.EVENT_LBUTTONDOWN:

#reset

if topLeft_clicked and bottomRight_clicked:

topLeft_clicked = False

bottomRight_clicked = False

pt1 = (0,0)

pt2 = (0,0)

#get coordinates of top left corner

if not topLeft_clicked:

pt1 = (x,y)

topLeft_clicked = True

#get coordinates of bottom right corner

elif not bottomRight_clicked:

pt2 = (x,y)

bottomRight_clicked = True

#start actual program

#initially we haven't drawn anything

pt1 = (0,0)

pt2 = (0,0)

topLeft_clicked = False

bottomRight_clicked = False

#capture video

cap = cv2.VideoCapture('Path to video')

cv2.namedWindow(winname='myName')

cv2.setMouseCallback('myName', draw_rectangle)

firstFrame = True

while True:

ret, frame = cap.read()

gray_frame = cv2.cvtColor(frame, cv2.COLOR_BGR2GRAY)

while ret and firstFrame:

cv2.imshow('myName', gray_frame)

if topLeft_clicked:

cv2.circle(gray_frame, center=pt1, radius=5, color=(255,0,0), thickness=-1)

if topLeft_clicked and bottomRight_clicked:

cv2.rectangle(gray_frame, pt1, pt2, (255,0,0), 2)

firstFrame = False

cv2.imshow('Estimate_Velocity', gray_frame)

if cv2.waitKey(1) &0xFF == ord('q'):

break

cap.release()

cv2.destroyAllWindows()