如何在多线程类之外运行 OpenCV VideoCapture 的读取功能？答案

【问题标题】：How to run OpenCV VideoCapture's read function outside multithreading class?如何在多线程类之外运行 OpenCV VideoCapture 的读取功能？
【发布时间】：2020-11-09 15:11:42
【问题描述】：

我正在使用Nathancy's SO code 从磁盘并行读取两个静态视频，利用多线程。以下修改后的代码对我来说非常好：

from threading import Thread
import cv2, time


class VideoStreamWidget(object):
    def __init__(self, src=0):
        self.capture = cv2.VideoCapture(src)
        # Start the thread to read frames from the video stream
        self.thread = Thread(target=self.update, args=())
        self.thread.daemon = True
        self.thread.start()

    def update(self):
        # Read the next frame from the stream in a different thread
        while True:
            if self.capture.isOpened():
                (self.status, self.image) = self.capture.read()
                self.frame = cv2.resize(self.image, (640, 480))
            time.sleep(.01)

    def show_frame(self, win_name='frame_1'):
        # Display frames in main program
        cv2.imshow(win_name, self.frame)
        key = cv2.waitKey(1)
        if key == ord('q'):
            self.capture.release()
            cv2.destroyAllWindows()
            exit(1)

if __name__ == '__main__':
    video_stream_widget1 = VideoStreamWidget(src=r'C:\Users\ab\Documents\Video\ch6.asf')
    video_stream_widget2 = VideoStreamWidget(
        src=r'C:\Users\ab\Documents\Video\ch4.asf')
    while True:
        try:
            video_stream_widget1.show_frame('frame_1')
            video_stream_widget2.show_frame('frame_2')
        except AttributeError:
            pass

现在我正在尝试调整上面的代码，因为我想在类外部创建一个 while 循环，并从 capture.read() 函数中获取状态和图像，以供其他代码在循环中逐帧使用.但是，它甚至不适用于带有此（断言 fctx->async_lock failed at libavcodec/pthread_frame.c:155）错误的单个视频流。代码如下：

from threading import Thread
import cv2, time


class VideoStreamWidget(object):
    def __init__(self, src=0):
        self.capture = cv2.VideoCapture(src)
        # Start the thread to read frames from the video stream
        self.thread = Thread(target=self.update, args=())
        self.thread.daemon = True
        self.thread.start()

    def update(self):
        # Read the next frame from the stream in a different thread
        while True:
            if self.capture.isOpened():
                (self.status, self.image) = self.capture.read()
                self.frame = cv2.resize(self.image, (640, 480))
            # time.sleep(.01)

    # def show_frame(self, win_name='frame_1'):
    #     # Display frames in main program
    #     cv2.imshow(win_name, self.frame)
    #     key = cv2.waitKey(1)
    #     if key == ord('q'):
    #         self.capture.release()
    #         cv2.destroyAllWindows()
    #         exit(1)

if __name__ == '__main__':
    video_stream_widget1 = VideoStreamWidget(src=r'C:\Users\ab\Documents\Video\ch6.asf')
    # video_stream_widget2 = VideoStreamWidget(
    #     src=r'C:\Users\ab\Documents\Video\ch4.asf')
    # while True:
    #     try:
    #         video_stream_widget1.show_frame('frame_1')
    #         video_stream_widget2.show_frame('frame_2')
    #     except AttributeError:
    #         pass
    while True:
        vflag, image_np = video_stream_widget1.status, video_stream_widget1.frame
        print(image_np)

这是一个 setter getter 问题吗？你能帮忙指出我哪里出错了吗？

【问题讨论】：

标签： python-3.x multithreading opencv python-multithreading video-capture

【解决方案1】：

尝试了几种方法后，在init中添加self.status、self.image和self.frame解决了这个问题。由于是多线程的，我们需要在构造函数中显式初始化这些变量。

【讨论】：