python cv2获取视频第一帧，并转码

安装Python库 sudo pip install opencv-python 或者sudo pip install opencv-python -i https://pypi.douban.com/simple/

 1 #get first frame
 2 import os
 3 import cv2
 4 import base64
 5 mp4_loc='./a.mp4'
 6 first_frame_loc='./first_frame.jpg'
 7 videoCapture = cv2.VideoCapture(mp4_loc)
 8 success, frame = videoCapture.read()
 9 if(success):
10     cv2.imwrite(first_frame_loc,frame)
11 os.remove(mp4_loc)  #delete mp4 file
12 with open(first_frame_loc, 'rb') as f:
13     first_frame_pic_64=base64.b64encode(f.read())

1、videoCapture = cv2.VideoCapture(mp4_loc)

VideoCapture()中参数是mp4_loc，表示打开视频，参数是0则表示打开笔记本的内置摄像头，如cap = cv2.VideoCapture(0)

2、success, frame = videoCapture .read()

videoCapture .read()按帧读取视频，success, frame是获cap.read()方法的两个返回值。其中success是布尔值，如果读取帧是正确的则返回True，如果文件读取到结尾，它的返回值就为False。frame就是每一帧的图像，是个三维矩阵。

参考：https://blog.csdn.net/Zhou_yongzhe/java/article/details/80310537