如何實時模擬視頻並能夠提取其幀？

Question

我正在制作一個識別視頻中人物的程序。 使用 OpenCV 您可以提取視頻的幀，如下所示（我正在使用 c++）：

cv::VideoCapture vidCap(path/video.mp4);
cv::Mat frame;
while (!endVideo){
     successRead = vidCap.read(frame);
     if (!successRead){
         endVideo = true;
     }
/* work */
}

這對於視頻來說很好，但在未來，我將使用相機。 因此，我想用這個視頻“path/video.mp4”來模擬它，就好像它是一個相機一樣，也就是說，我希望它實時運行，並且我的程序要捕捉實時運行的視頻幀（即使它丟失了一些幀）。

偽代碼將是（我不關心庫）：

video.load(path/video.mp4) //load video
video.run()                //run video
while (!endVideo){
  video.getFrame(frame);  //get frame, even if it's the 10 frame
/* work */
}

Answer 1

一種方法可能是啟動一個單獨的線程，以正常速度讀取視頻文件並將每一幀填充到一個全局變量中。 然后，主線程在准備好時就抓取該幀。

因此，如果我們使用僅顯示時間和幀計數器的視頻，我們可以在假相機更新幀時到處抓取幀：

#!/usr/bin/env python3

import cv2
import sys
import time
import logging
import numpy as np
import threading, queue

logging.basicConfig(level=logging.DEBUG, format='%(levelname)s %(message)s')

# This is shared between main and the FakeCamera
currentFrame = None

def FakeCamera(Q, filename):
    """Reads the video file at its natural rate, storing the frame in a global called 'currentFrame'"""
    logging.debug(f'[FakeCamera] Generating video stream from {filename}')

    # Open video
    video = cv2.VideoCapture(filename)
    if (video.isOpened()== False):
       logging.critical(f'[FakeCamera] Unable to open video {filename}')
       Q.put('ERROR')
       return

    # Get height, width and framerate so we know how often to read a frame
    h   = int(video.get(cv2.CAP_PROP_FRAME_HEIGHT))
    w   = int(video.get(cv2.CAP_PROP_FRAME_WIDTH))
    fps = video.get(cv2.CAP_PROP_FPS)
    logging.debug(f'[FakeCamera] h={h}, w={w}, fps={fps}')

    # Initialise currentFrame
    global currentFrame
    currentFrame = np.zeros((h,w,3), dtype=np.uint8)

    # Signal main that we are ready
    Q.put('OK')

    while True:
        ret,frame = video.read()
        if ret == False:
            break
        # Store video frame where main can access it
        currentFrame[:] = frame[:]
        # Try and read at appropriate rate
        time.sleep(1.0/fps)

    logging.debug('[FakeCamera] Ending')
    Q.put('DONE')

if __name__ == '__main__':

    #  Create a queue for synchronising and communicating with our fake camera
    Q = queue.Queue()

    # Create a fake camera thread that reads the video in "real-time"
    fc = threading.Thread(target=FakeCamera, args=(Q,'video.mov'))
    fc.start()

    # Wait for fake camera to intialise
    logging.debug(f'[main] Waiting for camera to power up and initialise')
    msg = Q.get()
    if msg != 'OK':
        sys.exit()

    # Main processing loop should go here - we'll just grab a couple frames at different times
    cv2.imshow('Video',currentFrame)
    res = cv2.waitKey(2000)

    cv2.imshow('Video',currentFrame)
    res = cv2.waitKey(5000)

    cv2.imshow('Video',currentFrame)
    res = cv2.waitKey(2000)

    # Wait for buddy to finish
    fc.join()

樣品 Output

DEBUG [FakeCamera] Generating video stream from video.mov
DEBUG [main] Waiting for camera to power up and initialise
DEBUG [FakeCamera] h=240, w=320, fps=25.0
DEBUG [FakeCamera] Ending

關鍵詞：Python，圖像處理，OpenCV，多線程，多線程，多線程，多線程，視頻，假相機。