python opencv在网络摄像头视频中使用putText显示时间倒计时

Question

目标：

我想在网络摄像头获得的每一帧上放置文本，以便文本“3”、“2”、“1”可以分别显示一秒钟。从而描绘了一个倒数计时器。倒计时后，应将帧写入文件，即保存到磁盘。只要视频流尚未关闭，这应该是可重复的。

每一帧都是在一个while循环中获得的，由于硬件配置的原因，相机可能有一个未知的帧速率，或者更糟的是，相机每秒检索的帧数在相机运行过程中可能会发生变化。

time.sleep() 无法使用，因为它会冻结 while 循环并中断正在窗口中显示的视频流。

主 while 循环中的另一个 while 循环是不可接受的，因为它大大降低了处理器的速度，并且每秒处理的帧数更少，从而使视频流非常不稳定。

我的尝试：

import cv2
import sys
import time

# Initialize variables
camSource = -1
running = True
saveCount = 0
nSecond = 1
totalSec = 3.0
keyPressTime = 0.0
startTime = 0.0
timeElapsed = 0.0
startCounter = False
endCounter = False

# Start the camera
camObj = cv2.VideoCapture(camSource)
if not camObj.isOpened():
    sys.exit('Camera did not provide frame.')

frameWidth = int(camObj.get(cv2.cv.CV_CAP_PROP_FRAME_WIDTH))
frameHeight = int(camObj.get(cv2.cv.CV_CAP_PROP_FRAME_HEIGHT))

# Start video stream
while running:
    readOK, frame = camObj.read()

    # Display counter on screen before saving a frame
    if startCounter:
        if nSecond <= totalSec: 
            # draw the Nth second on each frame 
            # till one second passes  
            cv2.putText(img = frame, 
                        text = str(nSecond),
                        org = (int(frameWidth/2 - 20),int(frameHeight/2)), 
                        fontFace = cv2.FONT_HERSHEY_DUPLEX, 
                        fontScale = 3, 
                        color = (255,0,0),
                        thickness = 2, 
                        lineType = cv2.CV_AA)

            timeElapsed += (time.time() - startTime)
            print 'timeElapsed:{}'.format(timeElapsed)

            if timeElapsed >= 1:
                nSecond += 1
                print 'nthSec:{}'.format(nSecond)
                timeElapsed = 0
                startTime = time.time()

        else:
            # Save the frame
            cv2.imwrite('img' + str(saveCount) + '.jpg', frame)  
            print 'saveTime: {}'.format(time.time() - keyPressTime)

            saveCount += 1
            startCounter = False
            nSecond = 1

    # Get user input
    keyPressed = cv2.waitKey(3)
    if keyPressed == ord('s'):
        startCounter = True
        startTime = time.time()
        keyPressTime = time.time()
        print 'startTime: {}'.format(startTime)
        print 'keyPressTime: {}'.format(keyPressTime)

    elif keyPressed == ord('q'):
        # Quit the while loop
        running = False
        cv2.destroyAllWindows()

    # Show video stream in a window    
    cv2.imshow('video', frame)

camObj.release()

问题：

我可以看到我的方法几乎可以工作，但time.time() 返回的 cpu 滴答声与现实世界的秒数不同。每个数字的文本一秒钟都没有显示，并且文件保存得太快（在 1.5 秒内而不是 3 秒内）。

我会接受：

如果您可以展示如何正确计时以及如何显示“3”、“2”、“1”而不是我当前显示“1”、“2”、“3”的方法

Answer 1

在挣扎了两天并阅读了datetime 模块后，我得到了我需要的东西。但是，如果它更 Pythonic，我可以接受除我之外的答案。

import cv2
import sys
from datetime import datetime

# Initialize variables
camSource = -1
running = True
saveCount = 0
nSecond = 0
totalSec = 3
strSec = '321'
keyPressTime = 0.0
startTime = 0.0
timeElapsed = 0.0
startCounter = False
endCounter = False

# Start the camera
camObj = cv2.VideoCapture(camSource)
if not camObj.isOpened():
    sys.exit('Camera did not provide frame.')

frameWidth = int(camObj.get(cv2.cv.CV_CAP_PROP_FRAME_WIDTH))
frameHeight = int(camObj.get(cv2.cv.CV_CAP_PROP_FRAME_HEIGHT))

# Start video stream
while running:
    readOK, frame = camObj.read()

    # Display counter on screen before saving a frame
    if startCounter:
        if nSecond < totalSec: 
            # draw the Nth second on each frame 
            # till one second passes  
            cv2.putText(img = frame, 
                        text = strSec[nSecond],
                        org = (int(frameWidth/2 - 20),int(frameHeight/2)), 
                        fontFace = cv2.FONT_HERSHEY_DUPLEX, 
                        fontScale = 6, 
                        color = (255,255,255),
                        thickness = 5, 
                        lineType = cv2.CV_AA)

            timeElapsed = (datetime.now() - startTime).total_seconds()
#            print 'timeElapsed: {}'.format(timeElapsed)

            if timeElapsed >= 1:
                nSecond += 1
#                print 'nthSec:{}'.format(nSecond)
                timeElapsed = 0
                startTime = datetime.now()

        else:
            cv2.imwrite('img' + str(saveCount) + '.jpg', frame)  
#            print 'saveTime: {}'.format(datetime.now() - keyPressTime)

            saveCount += 1
            startCounter = False
            nSecond = 1

    # Get user input
    keyPressed = cv2.waitKey(3)
    if keyPressed == ord('s'):
        startCounter = True
        startTime = datetime.now()
        keyPressTime = datetime.now()
#        print 'startTime: {}'.format(startTime)
#        print 'keyPressTime: {}'.format(keyPressTime)

    elif keyPressed == ord('q'):
        # Quit the while loop
        running = False
        cv2.destroyAllWindows()

    # Show video stream in a window    
    cv2.imshow('video', frame)

camObj.release()

Answer 2

这是我自己实现的一个版本，在 10 秒视频输出之前 5 秒倒数计时器的无缝显示！在 cmets 有任何问题请告诉我！

    def draw_text(frame, text, x, y, color=(255,0,255), thickness=4, size=3):
            if x is not None and y is not None:
                cv2.putText(
                    frame, text, (int(x), int(y)), cv2.FONT_HERSHEY_SIMPLEX, size, color, thickness)

    import numpy as np
    import cv2
    import time
    #timeout = time.time() + 11   # 10 seconds from now
    cap = cv2.VideoCapture(0)
    init_time = time.time()
    test_timeout = init_time+6
    final_timeout = init_time+17
    counter_timeout_text = init_time+1
    counter_timeout = init_time+1
    counter = 5
    while(cap.isOpened()):
        ret, frame = cap.read()
        if ret==True:
            center_x = int(frame.shape[0]/2)
            center_y = int(frame.shape[0]/2)
            if (time.time() > counter_timeout_text and time.time() < test_timeout):
                draw_text(frame, str(counter), center_x, center_y)
                counter_timeout_text+=0.03333
            if (time.time() > counter_timeout and time.time() < test_timeout):
                counter-=1
                counter_timeout+=1
            cv2.imshow('frame', frame)
            if (cv2.waitKey(1) & 0xFF == ord('q')) or (time.time() > final_timeout):
                break
        else:
            break
    # Release everything if job is finished
    cap.release()
    cv2.destroyAllWindows()