python - Opencv2 : Python: cv2. VideoWriter

Question

为什么下面的代码没有保存视频？另外，网络摄像头的帧速率是否必须与 VideoWriter 帧大小完全匹配？

import numpy as np
import cv2
import time

def videoaufzeichnung(video_wdth, video_hight, video_fps, seconds):
    cap = cv2.VideoCapture(6)
    cap.set(3, video_wdth) # wdth
    cap.set(4, video_hight) #hight 
    cap.set(5, video_fps) #hight 
    
    # Define the codec and create VideoWriter object
    fps = cap.get(5)
    fourcc = cv2.VideoWriter_fourcc(*'XVID')
    out = cv2.VideoWriter('output.avi', fourcc, video_fps, (video_wdth, video_hight))
    #out = cv2.VideoWriter('output.avi', fourcc, 20.0, (640, 480))
    
    start = time.time()
    zeitdauer = 0
    while(zeitdauer < seconds):
        end = time.time()
        zeitdauer = end - start
        ret, frame = cap.read()
        if ret == True:
            frame = cv2.flip(frame, 180)
            # write the flipped frame
            out.write(frame)
    
            cv2.imshow('frame', frame)
            if cv2.waitKey(1) & 0xFF == ord('q'):
                break
        else:
            break
    
    # Release everything if job is finished
    cap.release()
    out.release()
    cv2.destroyAllWindows()

videoaufzeichnung.videoaufzeichnung(1024, 720, 10, 30)

Answer 1

我怀疑您正在使用 libv4l 版本的 OpenCV 进行视频 I/O。 OpenCV 的 libv4l API 中存在一个错误，该错误会阻止 VideoCapture::set 方法更改视频分辨率。查看链接 1 , 2和 3 .如果您执行以下操作:

...
frame = cv2.flip(frame,180)
print(frame.shape[:2] # check to see frame size
out.write(frame)
...

您会注意到帧大小没有被修改以匹配函数参数中提供的分辨率。克服此限制的一种方法是手动调整框架大小以匹配分辨率参数。

...
frame = cv2.flip(frame,180)
frame = cv2.resize(frame,(video_wdth,video_hight)) # manually resize frame
print(frame.shape[:2] # check to see frame size
out.write(frame)
...