VideoWriter 输出损坏的视频文件

Question

这是我保存 web_cam 流的代码。它正在工作，但输出视频文件的问题。

import numpy as np
import cv2

cap = cv2.VideoCapture(0)

# Define the codec and create VideoWriter object
#fourcc = cv2.cv.CV_FOURCC(*'DIVX')
#out = cv2.VideoWriter('output.avi',fourcc, 20.0, (640,480))
out = cv2.VideoWriter('output.avi', -1, 20.0, (640,480))

while(cap.isOpened()):
    ret, frame = cap.read()
    if ret==True:
        frame = cv2.flip(frame,0)

        # 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()

Answer 1

下面是一些将帧保存到视频文件中的简单代码。我建议创建另一个线程来获取帧，因为它cv2.VideoCapture.read()是阻塞的。这可能会很昂贵并且会导致延迟，因为主线程必须等待直到获得帧。通过将此操作放入一个单独的线程中，该线程仅专注于在主线程中抓取帧并处理/保存帧，由于 I/O 延迟减少，它显着提高了性能。您还可以尝试其他编解码器，但使用 MJPG 应该是安全的，因为它内置于 OpenCV 中。

from threading import Thread
import cv2

class WebcamVideoWriter(object):
    def __init__(self, src=0):
        # Create a VideoCapture object
        self.capture = cv2.VideoCapture(src)

        # Default resolutions of the frame are obtained (system dependent)
        self.frame_width = int(self.capture.get(3))
        self.frame_height = int(self.capture.get(4))

        # Set up codec and output video settings
        self.codec = cv2.VideoWriter_fourcc('M','J','P','G')
        self.output_video = cv2.VideoWriter('output.avi', self.codec, 30, (self.frame_width, self.frame_height))

        # Start the thread to read frames from the video stream
        self.thread = Thread(target=self.update, args=())
        self.thread.daemon = True
        self.thread.start()

    def update(self):
        # Read the next frame from the stream in a different thread
        while True:
            if self.capture.isOpened():
                (self.status, self.frame) = self.capture.read()

    def show_frame(self):
        # Display frames in main program
        if self.status:
            cv2.imshow('frame', self.frame)

        # Press Q on keyboard to stop recording
        key = cv2.waitKey(1)
        if key == ord('q'):
            self.capture.release()
            self.output_video.release()
            cv2.destroyAllWindows()
            exit(1)

    def save_frame(self):
        # Save obtained frame into video output file
        self.output_video.write(self.frame)

if __name__ == '__main__':
    webcam_videowriter = WebcamVideoWriter()
    while True:
        try:
            webcam_videowriter.show_frame()
            webcam_videowriter.save_frame()
        except AttributeError:
            pass

Answer 2

由于帧速率和帧分辨率错误，输出文件已损坏。使用此代码：

out = cv2.VideoWriter('output.avi', -1, 20.0, (640,480))

我们将 fps/每秒帧速率设置为 20。这是不正确的。另外，框架的宽度和高度也是错误的。我通过从捕获的 web_cam 配置文件中获取 fps、宽度、高度来解决。

cap = cv2.VideoCapture(0)  #web-cam capture

fps = cap.get(cv2.CAP_PROP_FPS)
width  = cap.get(cv2.CAP_PROP_FRAME_WIDTH)   # float
height = cap.get(cv2.CAP_PROP_FRAME_HEIGHT)  # float
out = cv2.VideoWriter('output.avi', -1,fps, (int(width), int(height)))