How to get the duration of video using cv2

问题

I can only get the number of frames CAP_PROP_FRAME_COUNT using CV2.

However, I cannot find the parameter to get the duration of the video using cv2.

How to do that?

Thank you very much.

回答1:

cv2 is not designed to explore video metadata, so VideoCapture doesn't have API to retrieve it directly.

You can instead "measure" the length of the stream: seek to the end, then get the timestamp:

>>> v=cv2.VideoCapture('sample.avi')
>>> v.set(cv2.CAP_PROP_POS_AVI_RATIO,1)
True
>>> v.get(cv2.CAP_PROP_POS_MSEC)
213400.0

Checking shows that this sets the point after the last frame (not before it), so the timestamp is indeed the exact total length of the stream:

>>> v.get(cv2.CAP_PROP_POS_FRAMES)
5335.0
>>>> v.get(cv2.CAP_PROP_FRAME_COUNT)
5335.0

>>> v.set(cv2.CAP_PROP_POS_AVI_RATIO,0)
>>> v.get(cv2.CAP_PROP_POS_FRAMES)
0.0        # the 1st frame is frame 0, not 1, so "5335" means after the last frame

回答2:

In OpenCV 3, the solution is:

import cv2

cap = cv2.VideoCapture("./video.mp4")
fps = cap.get(cv2.CAP_PROP_FPS)      # OpenCV2 version 2 used "CV_CAP_PROP_FPS"
frame_count = int(cap.get(cv2.CAP_PROP_FRAME_COUNT))
duration = frame_count/fps

print('fps = ' + str(fps))
print('number of frames = ' + str(frame_count))
print('duration (S) = ' + str(duration))
minutes = int(duration/60)
seconds = duration%60
print('duration (M:S) = ' + str(minutes) + ':' + str(seconds))

cap.release()

回答3:

First calculate frame per second like this

fps = cap.get(cv2.cv.CV_CAP_PROP_FPS)

Then duration can be calculated as (number of frames) / (frames per second)

 duration = float(num_frames) / float(fps) # in seconds

回答4:

I noticed a weird phenomenon that many video DO NOT HAVE as much frames as the vid.get(cv2.CAP_PROP_FRAME_COUNT) gets.

I suppose that the video duration should be the divided value of TOTAL FRAMES by FPS, but it always mismatch. The video duration would be longer than we calculated. Considering what FFMPEG does, the original video might has some empty frames.

Hope this help.

来源：https://stackoverflow.com/questions/49048111/how-to-get-the-duration-of-video-using-cv2