openCV video saving in python

Question

I am trying to save the video but it s not working  I followed the instructions from the openCV documentation   import numpy as np import cv2  cap   cv2 VideoCapture 0   fourcc   cv2 VideoWriter fourcc   XVID   out   cv2 VideoWriter  output avi   fourcc  20 0   640 480    while cap isOpened         ret  frame   cap read       if ret  True          frame   cv2 flip frame 0            out write frame           cv2 imshow  frame  frame          if cv2 waitKey 1   amp  0xFF    ord  q                break     else          break cap release    out release    cv2 destroyAllWindows     What is wrong

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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

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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  640x480  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

User · Answer

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

User · Answer

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

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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   amp  0xFF    ord  q                break     else          break    Release everything if job is finished cap release   out release   cv2 destroyAllWindows

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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

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As                  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

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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

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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

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Try this  It s working for me  Windows 10   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   amp  0xFF    ord  q                break     else          break    Release everything if job is finished cap release   out release   cv2 destroyAllWindows

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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   amp  0xFF    ord  q            break  cap release   out release   cv2 destroyAllWindows

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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    quot output mp4 quot  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   amp  0xFF    ord  q            break cap release   out release   cv2 destroyAllWindows

User · Answer

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

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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   amp  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

[python] openCV video saving in python

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