在Python中从VideoCapture opencv获取特定帧 [英] Getting specific frames from VideoCapture opencv in python

问题描述

我有以下代码，该代码通过在python的opencv中使用VideoCapture库连续从视频中获取所有帧:

I have the following code, which continuously fetches all the frames from a video by using VideoCapture library in opencv in python:

import cv2

def frame_capture:
        cap = cv2.VideoCapture("video.mp4")
        while not cap.isOpened():
                cap = cv2.VideoCapture("video.mp4")
                cv2.waitKey(1000)
                print "Wait for the header"

        pos_frame = cap.get(cv2.cv.CV_CAP_PROP_POS_FRAMES)
        while True:
                flag, frame = cap.read()
                if flag:
                        # The frame is ready and already captured
                        cv2.imshow('video', frame)
                        pos_frame = cap.get(cv2.cv.CV_CAP_PROP_POS_FRAMES)
                        print str(pos_frame)+" frames"
                else:
                        # The next frame is not ready, so we try to read it again
                        cap.set(cv2.cv.CV_CAP_PROP_POS_FRAMES, pos_frame-1)
                        print "frame is not ready"
                        # It is better to wait for a while for the next frame to be ready
                        cv2.waitKey(1000)

                if cv2.waitKey(10) == 27:
                        break
                if cap.get(cv2.cv.CV_CAP_PROP_POS_FRAMES) == cap.get(cv2.cv.CV_CAP_PROP_FRAME_COUNT):
                        # If the number of captured frames is equal to the total number of frames,
                        # we stop
                        break

但是我想在视频的特定时间戳中获取特定的帧.

But I want to grab a specific frame in a specific timestamp in the video.

我该如何实现?

推荐答案

您可以使用VideoCapture的set()函数.

You can use set() function of VideoCapture.

您可以计算总帧数:

cap = cv2.VideoCapture("video.mp4")
total_frames = cap.get(7)

此处7是prop-Id.您可以在 http://docs.opencv.org/2.4/中找到更多信息modules/highgui/doc/reading_and_writing_images_and_video.html

Here 7 is the prop-Id. You can find more here http://docs.opencv.org/2.4/modules/highgui/doc/reading_and_writing_images_and_video.html

之后您可以设置帧号，假设我要提取第100帧

After that you can set the frame number, suppose i want to extract 100th frame

cap.set(1, 100)
ret, frame = cap.read()
cv2.imwrite("path_where_to_save_image", frame)

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