openCV video saving in python

I had the same problem and then I tried this:

frame = cv2.flip(frame,180) 

instead of

frame= cv2.flip(frame,0) 

and it’s working.

Nuru answer actually works, only thing is remove this line frame = cv2.flip(frame,0) under if ret==True: loop which will output the video file without flipping

I also faced same problem but it worked when I used ‘MJPG’ instead of ‘XVID’

I used

fourcc = cv2.VideoWriter_fourcc(*'MJPG')

instead of

fourcc = cv2.VideoWriter_fourcc(*'XVID')

As an example :

fourcc = cv2.VideoWriter_fourcc(*'MJPG')
out_corner = cv2.VideoWriter('img_corner_1.avi',fourcc, 20.0, (640, 480))

At that place, have to define X,Y as width and height

But, when you create an image (a blank image for instance) you have to define Y,X as height and width :

    img_corner = np.zeros((480, 640, 3), np.uint8)

jveitchmichaelis at https://github.com/ContinuumIO/anaconda-issues/issues/223 provided a thorough answer. Here I copied his answer:

The documentation in OpenCV says (hidden away) that you can only write
to avi using OpenCV3. Whether that’s true or not I’ve not been able to
determine, but I’ve been unable to write to anything else.

However, OpenCV is mainly a computer vision library, not a video stream, codec and write one. Therefore, the developers tried to keep
this part as simple as possible. Due to this OpenCV for video
containers supports only the avi extension, its first version.

From: http://docs.opencv.org/3.1.0/d7/d9e/tutorial_video_write.html

My setup: I built OpenCV 3 from source using MSVC 2015, including
ffmpeg. I’ve also downloaded and installed XVID and openh264 from
Cisco, which I added to my PATH. I’m running Anaconda Python 3. I also
downloaded a recent build of ffmpeg and added the bin folder to my
path, though that shouldn’t make a difference as its baked into
OpenCV.

I’m running in Win 10 64-bit.

This code seems to work fine on my computer. It will generate a video
containing random static:

writer = cv2.VideoWriter("output.avi",
cv2.VideoWriter_fourcc(*"MJPG"), 30,(640,480))

for frame in range(1000):
    writer.write(np.random.randint(0, 255, (480,640,3)).astype('uint8'))

writer.release()

Some things I’ve learned through trial and error:

• Only use ‘.avi’, it’s just a container, the codec is the important thing.

• Be careful with specifying frame sizes. In the constructor you need to pass the frame size as (column, row) e.g. 640×480. However the
  array you pass in, is indexed as (row, column). See in the above
  example how it’s switched?

• If your input image has a different size to the VideoWriter, it will fail (often silently)

• Only pass in 8 bit images, manually cast your arrays if you have to (.astype(‘uint8’))
• In fact, never mind, just always cast. Even if you load in images using cv2.imread, you need to cast to uint8…
• MJPG will fail if you don’t pass in a 3 channel, 8-bit image. I get an assertion failure for this at least.
• XVID also requires a 3 channel image but fails silently if you don’t do this.
• H264 seems to be fine with a single channel image
• If you need raw output, say from a machine vision camera, you can use ‘DIB ‘. ‘RAW ‘ or an empty codec sometimes works. Oddly if I use
  DIB, I get an ffmpeg error, but the video is saved fine. If I use RAW,
  there isn’t an error, but Windows Video player won’t open it. All are
  fine in VLC.

In the end I think the key point is that OpenCV is not designed to be
a video capture library – it doesn’t even support sound. VideoWriter
is useful, but 99% of the time you’re better off saving all your
images into a folder and using ffmpeg to turn them into a useful
video.

In my case, I found that size of Writer have to matched with the frame size both from camera or files. So that I read the frame size first and apply to writer setting as below.

(grabbed, frame) = camera.read()
fshape = frame.shape
fheight = fshape[0]
fwidth = fshape[1]
print fwidth , fheight
fourcc = cv2.VideoWriter_fourcc(*'XVID')
out = cv2.VideoWriter('output.avi',fourcc, 20.0, (fwidth,fheight))

As @ปรีดา ตั้งนภากร said: the sizes of Writer have to match with the frame from the camera or files.

You can use such code to check if your camera is (640, 480) or not:

print(int(cap.get(3)), int(cap.get(4)))

For myself, I found my camera is (1280, 720) and replaced (640, 480) with (1280, 720). Then it can save videos.

Please make sure to set correct width and height. You can set it like bellow

cv2.VideoWriter('output.avi', fourcc, 20.0, (int(cap.get(3)), int(cap.get(4))))

This is an answer was only tested in MacOS but it will probably also work in Linux and Windows.

import numpy as np
import cv2

cap = cv2.VideoCapture(0)

# Get the Default resolutions
frame_width = int(cap.get(3))
frame_height = int(cap.get(4))

# Define the codec and filename.
out = cv2.VideoWriter('output.avi',cv2.VideoWriter_fourcc('M','J','P','G'), 10, (frame_width,frame_height))

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

        # write the  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()

You need to get the exact size of the capture like this:

import cv2

cap = cv2.VideoCapture(0)
width = int(cap.get(cv2.CAP_PROP_FRAME_WIDTH) + 0.5)
height = int(cap.get(cv2.CAP_PROP_FRAME_HEIGHT) + 0.5)
size = (width, height)
fourcc = cv2.VideoWriter_fourcc(*'XVID')
out = cv2.VideoWriter('your_video.avi', fourcc, 20.0, size)

while(True):
    _, frame = cap.read()
    cv2.imshow('Recording...', frame)
    out.write(frame)
    if cv2.waitKey(1) & 0xFF == ord('q'):
        break

cap.release()
out.release()
cv2.destroyAllWindows()

I wasn’t having codec issues or dimension issues as the answers above. Instead, my issue was because my output frames were in greyscale.

I had to create a VideoWriter with the parameter isColor=False

out = cv2.VideoWriter(output_path,
                      cv2.VideoWriter_fourcc(*'mp4v'),
                      30,
                      (INPUT_VIDEO_WIDTH,INPUT_VIDEO_HEIGHT),
                      isColor=False
                      )

In the API Docs, it wrongly says that the flag is currently supported on Windows only. I have tested on Ubuntu 20.04, with opencv-python==4.2.0.34, and it finally writes out to file correctly.

import cv2

cap = cv2.VideoCapture(0)

fourcc = cv2.VideoWriter_fourcc('X','V','I','D')
frame_width = int(cap.get(3))
frame_height = int(cap.get(4))

out = cv2.VideoWriter('output.mp4', fourcc, 20,(frame_width,frame_height),True )
print(int(cap.get(3)))
print(int(cap.get(4)))
while(cap.isOpened()):
    ret,frame = cap.read()
    if ret == True:
        print(frame.shape)
        out.write(frame)
        cv2.imshow('Frame', frame)
        if cv2.waitKey(1) & 0xFF == ord('q'):
            break
    else:
        break
cap.release()
out.release()`enter code here`

cv2.destroyAllWindows()

This works fine but the problem of having video size relatively very small means nothing is captured. So make sure the height and width of a video and the image that you are going to recorded is same. If you are using some manipulation after capturing a video than you must confirm the size (before and after).
Hope it will save some1’s hour

This answer covers what’s what in terms of variables and importantly, output size shall be same for input frame and video size.

import cv2

save_name = "output.mp4"
fps = 10
width = 600
height = 480
output_size = (width, height)
out = cv2.VideoWriter(save_name,cv2.VideoWriter_fourcc('M','J','P','G'), fps , output_size )

cap = cv2.VideoCapture(0) # 0 for webcam or you can put in videopath
while(True):
    _, frame = cap.read()
    cv2.imshow('Video Frame', frame)
    out.write(cv2.resize(frame, output_size ))
    if cv2.waitKey(1) & 0xFF == ord('q'):
        break
cap.release()
out.release()
cv2.destroyAllWindows()

I wanted to write a grayscale image and nothing worked for me, I had to add a 0 to VideoWriter

out = cv2.VideoWriter(outfilename, fourcc, fps, (width, height), 0)

I’m Kind of late, But VidGear Python Library’s WriteGear API automates the process of pipelining OpenCV frames into FFmpeg on any platform in real-time with Hardware Encoders support and at the same time provides same opencv-python syntax. Here’s a basic python example:

# import libraries
from vidgear.gears import WriteGear
import cv2

output_params = {"-vcodec":"libx264", "-crf": 0, "-preset": "fast"} #define (Codec,CRF,preset) FFmpeg tweak parameters for writer

stream = cv2.VideoCapture(0) #Open live webcam video stream on first index(i.e. 0) device

writer = WriteGear(output_filename = 'Output.mp4', compression_mode = True, logging = True, **output_params) #Define writer with output filename 'Output.mp4' 

# infinite loop
while True:
    
    (grabbed, frame) = stream.read()
    # read frames

    # check if frame empty
    if not is grabbed:
        #if True break the infinite loop
        break
    

    # {do something with frame here}
    gray = cv2.cvtColor(frame, cv2.COLOR_BGR2GRAY)

    # write a modified frame to writer
    writer.write(gray) 
       
    # Show output window
    cv2.imshow("Output Frame", frame)

    key = cv2.waitKey(1) & 0xFF
    # check for 'q' key-press
    if key == ord("q"):
        #if 'q' key-pressed break out
        break

cv2.destroyAllWindows()
# close output window

stream.release()
# safely close video stream
writer.close()
# safely close writer

Source:https://abhitronix.github.io/vidgear/latest/gears/writegear/compression/usage/#using-compression-mode-with-opencv

You can check out VidGear Docs for more advanced applications and features.

The other answers work for saving a single video feed. But if you have more then one video source, say numerous IP camera feeds, RTSP streams, or webcams, you may want to record them all at once. Here’s a method for saving multiple video feeds simultaneously using multithreading. The idea is to have two threads for each video source: 1) dedicated to only reading frames from the stream and 2) dedicated for processing frames (showing and saving).

Since cv2.VideoCapture.read() is a blocking operation, we must separate reading frames from saving frames. We can read frames in its own independent thread to improve performance by reducing latency due to I/O operations. By dedicating frame capture to its own thread, there will always be a frame ready to be processed instead of having to wait for the I/O operation to complete and return a fresh frame. The second thread is dedicated to processing and saving frames to the output file. We can encapsulate all of this into a single object, where it can be scaled regardless of the number of simultaneous video streams. Be sure to change the video src parameter to your own video source. Here’s an example of simultaneously recording three video streams.

from threading import Thread
import cv2
import time

class VideoWriterWidget(object):
    def __init__(self, video_file_name, src=0):
        # Create a VideoCapture object
        self.frame_name = str(src)
        self.video_file = video_file_name
        self.video_file_name = video_file_name + '.avi'
        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(self.video_file_name, 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()
        
        # Start another thread to show/save frames
        self.start_recording()
        print('initialized {}'.format(self.video_file))

    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(self.frame_name, 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)
    
    def start_recording(self):
        # Create another thread to show/save frames
        def start_recording_thread():
            while True:
                try:
                    self.show_frame()
                    self.save_frame()
                except AttributeError:
                    pass
        self.recording_thread = Thread(target=start_recording_thread, args=())
        self.recording_thread.daemon = True
        self.recording_thread.start()

if __name__ == '__main__':
    src1 = 'Your link1'
    video_writer_widget1 = VideoWriterWidget('Camera 1', src1)
    src2 = 'Your link2'
    video_writer_widget2 = VideoWriterWidget('Camera 2', src2)
    src3 = 'Your link3'
    video_writer_widget3 = VideoWriterWidget('Camera 3', src3)
        
    # Since each video player is in its own thread, we need to keep the main thread alive.
    # Keep spinning using time.sleep() so the background threads keep running
    # Threads are set to daemon=True so they will automatically die 
    # when the main thread dies
    while True:
        time.sleep(5)

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You have to specify the width and the height of the video according to the size of the image feed. Otherwise, it will create a file size of around 5.5KB.

result = cv2.VideoWriter(name,cv2.VideoWriter_fourcc(*'MJPG'), 10, (**960, 540**))