opencv 视频捕获和读取不会检索所有帧。 返回不正确的帧数

Question

I have a mp4 video which is 29 minutes long with 1536x2304 resolution. What I am trying do is to create a dataloader which ingest mp4 files and feeds to a CNN, but to do so I need to use opencv to retrieve the frames. When I use cap = cv.VideoCapture("mp4 file") and ret, frame = cap.read(), I only receive about 40 frames.

Since the Video is 29 min long, and it is 18fps, the number of frames I expect is around 31320 frames, but I only get 40. Really confused, any help is appreciated!

Answer 1

As you specified that you used the line ret, frame = cap.read() to count the number of frames, I would assume that you are using a while loop with a condition of when to break .

Have you considered that the while loop may have ended due to an issue unrelated to the number of frames in the VideoCapture object? Or you may have called the cap.read() method multiple times per increment to the variable you used to count the frames with.

The proper way to get the number of frames in a video using OpenCV would be:

import cv2 as cv

cap = cv.VideoCapture("file.mp4")
count = cap.get(cv2.CAP_PROP_FRAME_COUNT)

print(count)

(Note: If you get the output 0 , then the filename specified likely couldn't be found and would need to be corrected.)