python - 从python中的VideoCapture opencv获取特定帧

Question

我有以下代码，它通过在 python 中使用 opencv 中的 VideoCapture 库从视频中连续获取所有帧:

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

但我想抓取视频中特定时间戳中的特定帧。

我怎样才能做到这一点？

Answer 1

您可以使用 VideoCapture 的 set() 函数。

您可以计算总帧数:

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

这里的 7 是 prop-Id。您可以在这里找到更多信息 http://docs.opencv.org/2.4/modules/highgui/doc/reading_and_writing_images_and_video.html

然后你可以设置帧数，假设我想提取第100帧

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