OpenCV videowrite doesn't write video

Question

I used the following page from OpenCV 3.0.0 tutorial: Tutorial in docs

When I tried to use the example that saves videos, it doesn't work.

It displays the content from the webcam, and also creates a file called output.avi, but when I checked the size of ouput.avi, it was zero bytes.

I also tried using different codecs, like YUY2.

I use Python 2.7.8 and OpenCV 3.0.0 and Windows 8.1

Fiscal

If anyone has a similar issue and is writing black and white image, you need to specify that the image is not in colour: out = cv2.VideoWriter('output.avi',fourcc, 20.0,(int(cap.get(3)),int(cap.get(4))), False) – Orelie

Answer 1

I had the same problem and I solved it by specifying the video output resolution to exactly the same as input:

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

Of course make sure you got ffmpeg installed and working.

Alonsoalonzo

Even if the input is from converted PIL image, make sure the size is the same! – Adjutant

Answer 2

I was struggling with this problem for a few hours then I realized that I had typed the image's shape wrong.

It is (width, height), ie:

(image.shape[1], image.shape[0])

and not

(image.shape[0], image.shape[1])

This is how my working code looks like finally... (I am on a Windows machine):

video_path = FILENAME + '.avi'
size = images[0].shape[1], images[0].shape[0] ## <<<--- NOTICE THIS
video = cv2.VideoWriter(video_path,cv2.VideoWriter_fourcc(*'DIVX'), 60, size)  

for img in images:  
    video.write(img)

cv2.destroyAllWindows()
video.close()

Transversal

Thank you so much. For me the problem is, that just DIVX as fourcc works. – Flameout

Thanks for this. I wish OpenCV raised an exception when it got a frame that didn't match the dims. That would have saved me a lot of time. – Milford

Answer 3

Replacing:

fourcc = cv2.VideoWriter_fourcc(*'XVID')

With:

fourcc = cv2.VideoWriter_fourcc('M','J','P','G')

Worked for me...

More generally:

Look up the fourcc code of the video compression format you're after here, and whatever the code is - for instance 'FMP4' for FFMpeg - plug it in in the following manner:

cv2.VideoWriter_fourcc('F','M','P','4')

Vietnam

Actually, (*'XVID') is the same as ('X', 'V', 'I', 'D') Take a look at docs.python.org/dev/tutorial/… – Ethelstan

Yes, cv2.VideoWriter_fourcc('M','J','P','G') is work. I use opencv 4. – Brew

Link is broken. – Pompom

Answer 4

Make sure you are using the correct fourcc 4-byte code. The example on the tutorial has:

fourcc = cv2.VideoWriter_fourcc(*'XVID')
out = cv2.VideoWriter('output.avi',fourcc, 20.0, (640,480))

This XVID code may only work for linux. The documentation above the example states (in the tutorial): "In Windows: DIVX (More to be tested and added)." So if you haven't, try replacing the fourcc line above with:

fourcc = cv2.VideoWriter_fourcc(*'DIVX')

I use cv2.VideoWriter on linux quite often and it always works. So if the above doesn't work you can always try it on a linux vm.

Linotype

Unfortunately, I cannot get it to work. DIVX doesn't work for me. Thanks for helping. – Fiscal

CV2 makes use of ffmpeg. It could be that cv2 is not finding the application. – Linotype

I looked through my code and found that I have this line: fourcc = cv2.cv.CV_FOURCC('X', 'V', 'I', 'D'). This is for a Linux vm but you could make appropriate changes and try it. I don't know where I originally found this code but it works for me. – Linotype

It doesn't work on Linux, Debian Stretch stable. If yes for you, then you are a lucky man. For me it has created the output file once properly, once with 0 bytes length and 500-times no file was created (no error reported; command timing as if all works excellent) :((( – Compressive

@Compressive I just tested it on ubuntu 16.04 with opencv3 installed and it is working for me. I tested with color image frames so as posted above I don't specify the isColor flag, however you may want to verify that you have this correctly set to True/False, as needed. This won't give an exception if you have it set incorrectly, you just get an "un-playable" video. If this doesn't help it may be that you need to install ffmpeg or alternative on your machine. – Linotype

Answer 5

In my case, I thought the codec was an obstacle but it wasn't. Instead, adjusting the dimensions being consumed by videoWriter() did the trick:

(ok, frame) = cv2.VideoCapture(videoPath).read()

 fourcc = cv2.VideoWriter_fourcc(*'XVID')
 out = cv2.VideoWriter(output, fourcc, 10.0, (1280, 720))

(1280,720) was used because frame.shape from my video outputs (1280, 720, 3). It made avi to mp4 and vice versa possible. Didn't have to worry about reconciling the codec.

Macklin

Answer 6

Check the resolution of your images! I was trying with odd-shaped images (1284x709) and ended up with unreadable videos of 1k in size. After resizing my image to the closest 'common' resolution: image = cv2.resize(image, (1280,720)), it worked just fine.

Derange

Also, check for an error message. I had on my jupyter notebook: OpenCV: FFMPEG: tag 0x5634504d/'MP4V' is not supported with codec id 13 and format 'mp4 / MP4 (MPEG-4 Part 14)' OpenCV: FFMPEG: fallback to use tag 0x7634706d/'mp4v', and by using the exact 4 letters as suggested (mp4v), respecting the case, the message disappeared. – Derange

Answer 7

I suspect there are a lot of reasons video writing fails silently, and in my case, my frame was a composite of a 3 channel image and a 4 channel image (transparent overlay). Converting the end result to BGR format as follows allowed the video to save successfully.

width = 1280
height = 720
FPS = 30
fourcc = VideoWriter_fourcc(*'avc1')
video = VideoWriter('output.mp4', fourcc, float(FPS), (width, height))
for img in images:
  frame = cv2.cvtColor(img, cv2.COLOR_BGRA2BGR)
  video.write(frame)
video.release()

Monogenesis

Answer 8

It should be a problem with the codec you're using.

Have you tried:

cv.CV_FOURCC('i', 'Y', 'U', 'V')

This one worked for me.

Gallenz

Answer 9

On windows 7 and using Python 2.7 and OpenCV 2.4.8, I experienced the fact that if the file NAME is "output.mpg" would not write.

I solved it by changing to "output.avi".

Gorge

Answer 10

I have the exact same issue. I am using OpenCV in C++, but I believe you can still pass -1 instead of choosing the codec so you can have a drop down menu of the available codecs even in python. From there I tried all different codecs and just like Leonard Zhou, the IYUV codec was the one that worked for me. Also note that it was the only one that worked even though I could use XVID just fine on another machine with the same code and same codec installer.

EDIT: What I suggested worked as a patch, the main issue was solved on my end by adding the opencv_ffmpeg dll in the executable's folder.

Lucerne

Answer 11

I changed the Video writer size to my screen resolution size and it worked.

here is the solution.

out = cv2.VideoWriter("output.avi", fourcc, 5.0, (1920, 1080))

Ugaritic

Answer 12

It worked for me after I assigned the actual frame size and not what I thought the size was:

ret, frame = cap.read()
height, width, channels = frame.shape
codec = cv2.VideoWriter_fourcc(*"DIVX")
out=cv2.VideoWriter('new.avi',codec ,20.0,(width, height))

And put out.write(frame) inside the while loop before cv2.imshow("Frame", frame).

Rosenwald

On my system, only 'DIVX' works whereas the encoding on the opencv documentation examples, 'M', 'J', 'P', 'G', just silently writes no file. I wish there was a way to verify the codec so that my code is more safely portable. – Haunted

Answer 13

After trying hours to find the error, I finally found it. So here are some things to keep in mind. (For Linux users particularly)

1. Use this codec ("MJPG").

   cv2.VideoWriter_fourcc(*'MJPG')
   

2. Do not forget to write the Boolean value as final argument (True for RGB and False for GrayScale) in

   cv2.VideoWriter(path, fourcc, float(frameRate), frameSize, True)
   

3. The argument, frameSize required by cv2.VideoWriter is a tuple of form (width, height) and not (height, width) which is the shape of image array if you open the image using cv2.read or Image.open. So don't forget to invert it.

Flin

Answer 14

To state the obvious, make sure you're giving not only a correct path, but also a video name. i.e. path/'video.avi' and not just path/. It will fail silently otherwise.

Slone

Answer 15

In my case I am resizing the image, but saving video with original size instead of new size.

Benevento

Answer 16

The above methods work only for RGB frames/images. Incase you are trying to write a grayscale image, pass a parameter 0 to the VideoWriter():

fourcc = cv2.VideoWriter_fourcc(*"MJPG")
out = cv2.VideoWriter('output.avi', fourcc, 30, size, 0)

Outhaul

Answer 17

I had same issue that the video file was being created without any errors but it won't run and had a size of few KBs. Here's how I resolved it;

1. Make sure you have passed FPS argument in float value.
2. The output resolution needs to be same as of input video resolution.

Unifoliolate

Answer 18

In my case, the folder did not exists. It fails silently .

os.makedirs(os.path.dirname(self.video_output_path_temp), exist_ok=True)
out = cv2.VideoWriter(self.video_output_path_temp, fourcc, frame_rate, (screen_width, screen_height))

Brigand

Answer 19

Install ffmpeg using

conda install -c conda-forge ffmpeg

Piselli

Answer 20

I had a similar problem on macOS Sonoma (14.1) and OpenCV 4.9 (in Python), but in my case the writer was not outputting because the directory (file path) I had specified did not exist.

I assumed that VideoWriter would create the directory, but found out that I needed to create the directory first before VideoWriter would write to it.

Cholecalciferol

Answer 21

I tried by creating its exe using pyinstaller Recorder.py it worked for me.

Remember before using pyinstaller you have to pip install pyinstaller.

Snip