saving a video with opencv python 3-CodePudding

I want to save a video after converting to gray scale. I don't know where exactly put the line out.write(gray_video). I use jupyter notebook with Python 3, and the Opencv library.

the code is:

import cv2
import numpy as np

video = cv2.VideoCapture("video1.mp4")

fourcc = cv2.VideoWriter_fourcc(*'XVID')
out = cv2.VideoWriter('out_gray_scale.mp4', fourcc, 10.0, (640,  480),0)

while (True):
   (ret, frame) = video.read()

   if not ret:
       print("Video Completed")
       break

   # Convert the frames into Grayscaleo
   gray_video = cv2.cvtColor(frame, cv2.COLOR_BGR2GRAY)

   #writing
   gray_frame = cv2.flip(gray_video, 0)
   out.write(gray_video)  #it suppose to save the gray video

   #Show the binary frames
   if ret == True:
      cv2.imshow("video grayscale",gray_video)
    
      #out.write(gray_video)
      # Press q to exit the video  
      if cv2.waitKey(25) & 0xFF == ord('q'):
           break
   else:
       break
video.release()
cv2.destroyAllWindows()

CodePudding user response：

The working video writer module of OpenCV depends on three main things:

the available/supported/installed codecs on the OS
getting the right codec and file extension combinations
the input video resolution should be same as output video resolution otherwise resize the frames before writing

If any of this is wrong openCV will probably write a very small video file which will not open in video player. The following code should work fine:

import cv2
import numpy as np

video = cv2.VideoCapture("inp.mp4")
video_width  = int(video.get(cv2.CAP_PROP_FRAME_WIDTH))   # float `width`
video_height = int(video.get(cv2.CAP_PROP_FRAME_HEIGHT))  # float `height`
video_fps = int(video.get(cv2.CAP_PROP_FPS))

print(video_width, video_height, video_fps)
fourcc = cv2.VideoWriter_fourcc('M','J','P','G')
out = cv2.VideoWriter('out_gray_scale1.avi', fourcc, video_fps, (video_width,  video_height),0)


while (True):
   ret, frame = video.read()

   if not ret:
       print("Video Completed")
       break

   # Convert the frames into Grayscale
   gray_video = cv2.cvtColor(frame, cv2.COLOR_BGR2GRAY)

   #Show the binary frames
   if ret == True:
      cv2.imshow("video grayscale",gray_video)

      #Writing video
      out.write(gray_video)

      # Press q to exit the video  
      if cv2.waitKey(25) & 0xFF == ord('q'):
           break
   else:
       break
video.release()
out.release()
cv2.destroyAllWindows()

CodePudding user response：

You did not say what the problem is, so I'm guessing the video file is unreadable.

You need to call out.release() when you're done. That writes some metadata/index structures to the video file.

If you don't do that, the video file will contain the data but it will be corrupted/unreadable.