目录
1.2.4——cap.get(propId) cap.set(propIDd，value)
1.2——视频处理
1.2.1——捕获视频 cv.VideoCapture
语法：cv.VideoCapture(device)
参数：device可以是设备索引（device index） 也可以是视频文件名称/地址 （the name of a video file）
import numpy as np
import cv2 as cv
cap = cv.VideoCapture(0)
if not cap.isOpened():
print("Cannot open camera")
exit()
while True:
# Capture frame-by-frame
ret, frame = cap.read()
# if frame is read correctly ret is True
if not ret:
print("Can't receive frame (stream end?). Exiting ...")
break
# Our operations on the frame come here
gray = cv.cvtColor(frame, cv.COLOR_BGR2GRAY)
# Display the resulting frame
cv.imshow('frame', gray)
if cv.waitKey(1) == ord('q'):
break
# When everything done, release the capture
cap.release()
cv.destroyAllWindows()1.2.2——cap.read()
ret，frame=cap.read()
-
cap.read()返回一个布尔值，这里用ret接收，如果为True,则说明每一帧图像都被正常读取
-
frame用于接收得到的每一帧图片
1.2.3——cap.isOpened()
if not cap.isOpened():
print("Cannot open camera")
exit()用于判断cap是否正常初始化，返回布尔值，正常则返回True
1.2.4——cap.get(propId) cap.set(propIDd，value)
-
可以使用函数 cap.get(propId) 来获得视频的一些参数信息。这里 propId 可以是 0 到 18 之间的任何整数。每一个数代表视频的一个属性,其中的一些值可以使用 cap.set(propId,value) 来修改,value 就是 你想要设置成的新值
-
可以使用 cap.get(3) 和 cap.get(4) 来查看每一帧的宽和高。 默认情况下得到的值是 640X480。但是可以使用 cap.set(3,320) 和 cap.set(4,240) 来把宽和高改成 320X240
-
propId有以下值：（以下值可以以数字代替，按顺序从0开始）
| CV_CAP_PROP_POS_MSEC | Current position of the video file in milliseconds(视频文件当前文件) |
|---|---|
| CV_CAP_PROP_POS_FRAMES | 0-based index of the frame to be decoded/captured next |
| CV_CAP_PROP_POS_AVI_RATIO | Relative position of the video file: 0 - start of the film, 1 - end of the film. |
| CV_CAP_PROP_FRAME_WIDTH | Width of the frames in the video stream |
| CV_CAP_PROP_FRAME_HEIGHT | Height of the frames in the video stream |
| CV_CAP_PROP_FPS | Frame rate |
| CV_CAP_PROP_FOURCC | 4-character code of codec |
| CV_CAP_PROP_FRAME_COUNT | Number of frames in the video file |
| CV_CAP_PROP_FORMAT | Format of the Mat objects returned by retrieve() |
| CV_CAP_PROP_MODE | Backend-specific value indicating the current capture mode |
| CV_CAP_PROP_BRIGHTNESS | Brightness of the image (only for cameras) |
| CV_CAP_PROP_CONTRAST | Contrast of the image (only for cameras) |
| CV_CAP_PROP_SATURATION | Saturation of the image (only for cameras) |
| CV_CAP_PROP_HUE | Hue of the image (only for cameras) |
| CV_CAP_PROP_GAIN | Gain of the image (only for cameras). |
| CV_CAP_PROP_EXPOSURE | Exposure (only for cameras) |
| CV_CAP_PROP_CONVERT_RGB | Boolean flags indicating whether images should be converted to RGB. |
| CV_CAP_PROP_WHITE_BALANCE | Currently unsupported |
| CV_CAP_PROP_RECTIFICATION | Rectification flag for stereo cameras (note: only supported by DC1394 v 2.x backend cur- rently) |
1.2.5——播放视频文件
import numpy as np
import cv2 as cv
cap = cv.VideoCapture('vtest.avi')
while cap.isOpened():
ret, frame = cap.read()
# if frame is read correctly ret is True
if not ret:
print("Can't receive frame (stream end?). Exiting ...")
break
gray = cv.cvtColor(frame, cv.COLOR_BGR2GRAY)
cv.imshow('frame', gray)
if cv.waitKey(1) == ord('q'):
break
cap.release()
cv.destroyAllWindows()-
将frame接收到的每一帧图片，一帧帧播放出来（imshow）
1.2.6——保存视频文件
语法：VideoWriter（output_filename，FourCC，fps，size）
参数：
-
output_filename：文件路径
-
FourCC：编码
-
fps：帧率 （每秒的帧数）
-
size：视频窗口画幅 (width，height)
编码设置：用cv.VideoWriter_fourcc()设置编码，常用编码格式有以下几种：
| FourCC | 视频文件后缀 |
|---|---|
| cv2.VideoWriter_fourcc('M', 'P', '4', 'V') | .mp4 |
| cv2.VideoWriter_fourcc('X', 'V', 'I', 'D') | .avi |