# 打开摄像头并灰度化显示
import cv2 as cv 
# 0表示摄像头的编号
capture = cv.VideoCapture(0)

while(True):
  # 获取一帧
  # 第1个参数ret(return value缩写)是一个布尔值，表示当前这一帧是否获取正确
  ret, frame = capture.read()
  # 将这帧转换为灰度图
  gray = cv.cvtColor(frame, cv.COLOR_BGR2GRAY)

  cv.imshow('frame', gray)
  if cv.waitKey(1) == ord('q'):
    break

# 获取捕获的分辨率
# propId可以直接写数字，也可以用OpenCV的符号表示
width, height = capture.get(3), capture.get(4)
print(width, height)

# 以原分辨率的一倍来捕获
capture.set(cv.CAP_PROP_FRAME_WIDTH, width * 2)
capture.set(cv.CAP_PROP_FRAME_HEIGHT, height * 2)

# opencv播放本地视频
import cv2 as cv

capture = cv.VideoCapture('E:/1.mp4')

while(capture.isOpened()):
  ret, frame = capture.read()
  gray = cv.cvtColor(frame, cv.COLOR_BGR2GRAY)

  cv.imshow('frame', gray)
  if cv.waitKey(30) == ord('q'):
    break

import cv2 as cv

capture = cv.VideoCapture(0)

# 定义编码方式并创建VideoWriter对象
fourcc = cv.VideoWriter_fourcc(*'MJPG')
outfile = cv.VideoWriter('output.avi', fourcc, 25., (640, 480))

while(capture.isOpened()):
  ret, frame = capture.read()

  if ret:
    outfile.write(frame) # 写入文件
    cv.imshow('frame', frame)
    if cv.waitKey(1) == ord('q'):
      break
  else:
    break