在 python 中从 VideoCapture opencv 获取特定帧
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Getting specific frames from VideoCapture opencv in python
提问by yusuf
I have the following code, which continuously fetches all the frames from a video by using VideoCapture library in opencv in python:
我有以下代码，它通过在 python 中的 opencv 中使用 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
But I want to grab a specific frame in a specific timestamp in the video.
但我想在视频的特定时间戳中抓取特定帧。
How can I achieve this?
我怎样才能做到这一点？
采纳答案by abhishek
You can use set() function of VideoCapture.
您可以使用 VideoCapture 的 set() 函数。
You can calculate total frames:
您可以计算总帧数：
cap = cv2.VideoCapture("video.mp4")
total_frames = cap.get(7)
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
这里 7 是 prop-Id。你可以在这里找到更多http://docs.opencv.org/2.4/modules/highgui/doc/reading_and_writing_images_and_video.html
After that you can set the frame number, suppose i want to extract 100th frame
之后你可以设置帧数，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)
回答by Eric De Luna
this is my first post so please don't rip into me if I don't follow protocol completely. I just wanted to respond to June Wang just in case she didn't figure out how to set the number of frames to be extracted, or in case anyone else stumbles upon this thread with that question:
这是我的第一篇文章，所以如果我不完全遵守协议，请不要攻击我。我只是想回复 June Wang 以防万一她不知道如何设置要提取的帧数，或者以防其他人偶然发现这个问题的线程：
The solution is the good ol' for loop:
解决方案是好的 ol' for 循环：
vid = cv2.VideoCapture(video_path)
for i in range(start_frame, how_many_frames_you_want):
vid.set(1, i)
ret, still = vid.read()
cv2.imwrite(f'{video_path}_frame{i}.jpg', still)
