VideoWriter outputs corrupted video file

Question

This is my code to save web_cam streaming. It is working but the problem with output video file.

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

Here's some simple code to save frames into a video file. I recommend creating another thread for obtaining the frames since cv2.VideoCapture.read() is blocking. This can be expensive and cause latency as the main thread has to wait until it has obtained a frame. By putting this operation into a separate thread that just focuses on grabbing frames and processing/saving the frames in the main thread, it dramatically improves performance due to I/O latency reduction. You also can experiment with other codecs but using MJPG should be safe since its built into OpenCV.

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

The output file is corrupted because of the wrong frame rate and frame resolution. Using this code :

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

We set the fps/frame rate per second 20. Which was not correct. Also, the frame width and height was wrong. I solved by getting fps, width, height from the captured web_cam profile.

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)))

Answer 3

I added codec parameter to function cv2.videowriter.

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))
fps = cap.get(cv2.CAP_PROP_FPS)
width = cap.get(cv2.CAP_PROP_FRAME_WIDTH)   # float
height = cap.get(cv2.CAP_PROP_FRAME_HEIGHT)
codec = cv2.VideoWriter_fourcc('M', 'J', 'P', 'G')
out = cv2.VideoWriter('output.avi',codec,fps, (int(width),\
                                                    int (height)))

#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()

I hope you may see what is different in my code and your code. Mine works now. Using MJPG codec for .avi extention the indention is a bit messed,please do forgive cause I am very first time user. The video file is no longer corrupt. I got the info from: Link