可以参考官方接口文档：官方接口手册

提高FPS处理性能，参考：https://www.pyimagesearch.com/2015/12/21/increasing-webcam-fps-with-python-and-opencv/
https://towardsdatascience.com/@datitran

读取视频

封装了一个类，和使用方法如下：

class WebcamVideoStream:
  def __init__(self, src, width, height):
      # initialize the video camera stream and read the first frame
      # from the stream
      self.stream = cv2.VideoCapture(src)
      self.stream.set(cv2.CAP_PROP_FRAME_WIDTH, width)
      self.stream.set(cv2.CAP_PROP_FRAME_HEIGHT, height)
      (self.grabbed, self.frame) = self.stream.read()

      # initialize the variable used to indicate if the thread should
      # be stopped
      self.stopped = False

  def start(self):
      # start the thread to read frames from the video stream
      Thread(target=self.update, args=()).start()
      return self

  def update(self):
      # keep looping infinitely until the thread is stopped
      while True:
          # if the thread indicator variable is set, stop the thread
          if self.stopped:
              return

          # otherwise, read the next frame from the stream
          (self.grabbed, self.frame) = self.stream.read()

  def read(self):
      # return the frame most recently read
      return self.frame

  def stop(self):
      # indicate that the thread should be stopped
      self.stopped = True
  
  # sources表示摄像头编号0,1,2...
  video_capture =   WebcamVideoStream(ConfigManager.get_sources(),
                                  ConfigManager.get_width(),
                                  ConfigManager.get_height()).start()
   while True:
      origin_frame = video_capture.read()
      
      # 显示帧
      cv2.imshow("video", origin_frame）
      if cv2.waitKey(1) & 0xFF == ord('q'):
          break

保存图像

# 第一个参数为文件名
cv2.imwrite('messigray.jpg', img)

默认imwrite会压缩图像，如果想保存高质量图像，需要加参数
[int( cv2.IMWRITE_JPEG_QUALITY), 100]，如：

cv2.imwrite('messigray.jpg', img, [int( cv2.IMWRITE_JPEG_QUALITY), 100])

转换图像

# BGR转为RGB
frame_rgb = cv2.cvtColor(frame, cv2.COLOR_BGR2RGB)
# BGR转为灰度图像
gray = cv2.cvtColor(frame, cv2.COLOR_BGR2GRAY)

获取某一个位置的b,g,r值

(b, g, r) = origin_frame[0, 0]
(b, g, r) = origin_frame[50, 100]

翻转图像

以下两行把图像翻转270度，4:3图像，翻转90度270度后可能会自动裁剪图片。所以，中心点我设的是(width/2, width/2)

M = cv2.getRotationMatrix2D((width/2, width/2), 270, 1)

while True:
  ret, frame1 = cap.read()
  
  frame = cv2.warpAffine(frame1, M, (width, width))

完整代码如下（翻转图像，并提取前景）,如果找不到imutils。pip install imutils：

import argparse
import cv2
import numpy as np
import imutils

# construct the argument parser and parse the arguments
ag = argparse.ArgumentParser()
ag.add_argument("-v", "--video", help="source of the video")
ag.add_argument("-a", "--min-area", type=int, default=500, help="minimum area size")
args = vars(ag.parse_args())

source = "0"
if args.get("video", None) is None:
  source = "0"
else:
  source = args["video"]

min_area = args["min_area"]

cap = cv2.VideoCapture(int(source))

fgbg = cv2. createBackgroundSubtractorMOG2()
kernel = cv2.getStructuringElement(cv2.MORPH_ELLIPSE,(3,3))

width = 800
height = 600
cap.set(3,width)
cap.set(4,width)

M = cv2.getRotationMatrix2D((width/2, width/2), 270, 1)

while True:
  ret, frame1 = cap.read()
  
  frame = cv2.warpAffine(frame1, M, (width, width))
  #frame = cv2.resize()

  fgmask = fgbg.apply(frame)

  (_,cnts, _) = cv2.findContours(fgmask.copy(), cv2.RETR_EXTERNAL, cv2.CHAIN_APPROX_SIMPLE)
  maxArea = 0

  for c in cnts:
      if cv2.contourArea(c) < 900:
          (x, y, w, h) = (0,0,0,0)
          continue
      else:
          m=c
          (x, y, w, h) = cv2.boundingRect(m)

  cv2.rectangle(frame, (x,y), (x+w, y+h), (0, 255, 0), 2)    

  cv2.imshow('original', frame)
  cv2.imshow('fg', fgmask)
  #cv2.imshow('normal', frame1)

  k = cv2.waitKey(30) & 0xff
  if k == 27:
      break

cap.release()
cv2.destroyAllWindows()

参考接口：

# read image
image = cv2.imread(source_path + "\\" + img)
      
# rotate image
rows,cols,_ = temp.shape
# rotate 45 degrees with 0.6 Scaling factor 
M1 = cv2.getRotationMatrix2D((cols/2, rows/2), 90, 1)
image_1 = cv2.warpAffine(image, M1, (cols, rows))
# rotate 90 degrees with 0.6 Scaling factor
M2 = cv2.getRotationMatrix2D((cols/2, rows/2), 180, 1)
image_2 = cv2.warpAffine(image, M2, (cols, rows))

保存视频

试了好几种编码格式，Centos7上*"MJPG"这个是可以的

# fourcc = cv2.VideoWriter_fourcc(*'XVID')
# fourcc = cv2.VideoWriter_fourcc(*'X264')
fourcc = cv2.VideoWriter_fourcc(*"MJPG")
# fourcc = cv2.VideoWriter_fourcc('M', 'P', '4', '2')

out_video_name = "/home/trade_info/" + self.__cur_trade_id + "/video" + str(id) + ".avi"
out = cv2.VideoWriter(out_video_name, fourcc, 6.0, (valid_width, height))

video_capture = WebcamVideoStream(src, width, height).start()
while True：
    ret, origin_frame = video_capture.read()
    out.write(frame)