Recently, due to the needs of the project, I often need to use OpenCV to read video. I often encounter a problem that an error will be reported after reading the video. Although it does not affect the code results, I really can’t stand being picky.

Error reporting procedures:

# -*-coding:utf-8-*-
"""
File Name: read_video.py
Program IDE: PyCharm
Create File By Author: Hong
"""
import cv2


def read_video(video_path: str):
    """
    OpenCV read video widget, solve the video read error problem
    :param video_path: input the path of the video file to be read
    :return: no return value
    """
    print('Video path:', video_path)
    cap = cv2.VideoCapture(video_path)
    while cap.isOpened():
        # get a frame
        ret, frame = cap.read()

        cv2.imshow("capture", frame)

        if cv2.waitKey(1) & 0xFF == ord('q'):
            break
    print('Read through the video!')
    cap.release()
    cv2.destroyAllWindows()


if __name__ == '__main__':
    path = r'D:\multi_insect_videos\multi_object00.mp4'
    read_video(path)

You can read the video normally, but the result will output an error

Traceback (most recent call last):
  File "E:/PyCharmDocument/create_ST_image/multi_insect_processing/crop_video_to_images.py", line 76, in <module>
    read_video(path)
  File "E:/PyCharmDocument/create_ST_image/multi_insect_processing/crop_video_to_images.py", line 65, in read_video
    cv2.imshow("capture", frame)
cv2.error: OpenCV(4.5.3) C:\Users\runneradmin\AppData\Local\Temp\pip-req-build-uzca7qz1\opencv\modules\imgproc\src\color.cpp:182: error: (-215:Assertion failed) !_src.empty() in function 'cv::cvtColor'

The reason is that after the video is finished, the imshow() function of OpenCV can’t read the frame and makes an error. Solution: add judgment before imshow(). Read-only when there are frames. Exit the loop directly when there are no frames.

Error-free code:

# -*-coding:utf-8-*-
"""
File Name: read_video.py
Program IDE: PyCharm
Create File By Author: Hong
"""
import cv2


def read_video(video_path: str):
    """
    OpenCV read video widget, solve the video read error problem
    :param video_path: input the path of the video file to be read
    :return: no return value
    """
    print('Video path:', video_path)
    cap = cv2.VideoCapture(video_path)
    while cap.isOpened():
        # get a frame
        ret, frame = cap.read()
        if not ret:
            break
        cv2.imshow("capture", frame)

        if cv2.waitKey(1) & 0xFF == ord('q'):
            break
    print('Read through the video!')
    cap.release()
    cv2.destroyAllWindows()


if __name__ == '__main__':
    path = r'D:\multi_insect_videos\multi_object00.mp4'
    read_video(path)

Program output results:

Video path: D:\multi_insect_videos\multi_object00.mp4
Read through the video!

Process finished with exit code 0