如何将多线程与 cv2.VideoCapture() 一起使用？

Question

我想显示两个或多个单独的视频，并使用 cv2 应用了轻微的图像处理。

如果我不使用 threading/multiprocessing 会浪费大量时间来显示使用 cv2.waitKey(timeThatCouldBeSpentFetchingAFrameForAnotherVideo) 的帧。

我尝试使用 threading，但它无法正常工作。我收到此警告：WARNING: nextEventMatchingMask should only be called from the Main Thread! This will throw an exception in the future.。这通常会导致崩溃。

所以，我决定尝试实现 multiprocessing，理论上它应该比 threading 处理更复杂的图像更快（对吗？？）。 I used this as an example. 但是，在这种情况下，我运行进入了另一个问题，这种方法只能让我获得视频的第一帧。另外，我尝试将 cv2.VideoCapture() 放在 Process 之外，但结果是：TypeError: cannot pickle 'cv2.VideoCapture' object.

这是我的代码：

class CamManager:
    def __init__(self):
        self.saving = Saving()
        self.cams = self.createCamObjList()
        self.buffers = [Buffer(cam.FPS*BUFFER_SIZE) for cam in self.cams]


    def createCamObjList(self):
        l = []
        for i, url in enumerate(STREAM_URLS):
            saved_data = self.saving.getDataFor(url)
            cam = BufferedCamera(url, i, saved_data)
            l.append(cam)
        return l


    def startStreamCapture(self):
        queue_for_cams = multiprocessing.Queue()
        processes = [multiprocessing.Process(
            target=cam.readloop, args=[queue_for_cams]).start() for cam in self.cams]
        while True:
            if not queue_for_cams.empty():
                from_queue = queue_for_cams.get()
                self.buffers[from_queue[0]].add(from_queue[1])



class BufferedCamera():
    def __init__(self, streamURL, cam_id, saved_data=None):
        self.streamURL = streamURL
        self.cam_id = cam_id

        # get current camera's framerate
        cam = cv2.VideoCapture(streamURL)
        self.FPS = cam.get(5)
        if self.FPS == 0:
            self.FPS = 24
        cam.release()
        print(f"Input res: {cam.get(3)}x{cam.get(4)} | FPS: {self.FPS}")

        # use that framerate to adjust the time between each iteration of mainloop
        self.period = int((1.0/self.FPS)*1000)


    def readloop(self, queue):
        while True:
            self.read(queue)

    
    def read(self, queue):
        cam = cv2.VideoCapture(self.streamURL)
        _, frame = cam.read()
        if frame is not None:
            queue.put((self.cam_id, frame))
        cv2.waitKey(self.period)

Answer 1

我通过在我的 Process 函数中和 readloop 之前创建 cv2.VideoCapture 对象来让 multiprocessing 工作：

def readloop(self, queue):
    cam = cv2.VideoCapture(self.streamURL)
    while True:
        self.read(queue, cam)

如何将多线程与 cv2.VideoCapture() 一起使用？

How to use multithreading with and cv2.VideoCapture()?

python

python-3.x

cv2