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
