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• VideoCapture() returns None in opencv & install opencv with ffmpeg

  16 décembre 2017, par Wentai Chen

  System : UBUNTU 16.04
  Python version : 3.5

  I would like to use cv2.VideoCapture() function to process my mp4 file. However, when I run the script below, I always get a result of None, so I am not able to continue my work after.

  import cv2
  
  video_cap = cv2.VideoCapture('demo.mp4')
  
  ret,frame = video_cap.read()
  
  print(ret,frame)
  
  
  
  result: False,None

  By searching a lot I realized the problem : opencv is not properly installed with ffmpeg, so that the video function in opencv does not work.

  However I didn’t find a efficient tutorial on how to properly install opencv. I wonder if anyone could help. Thank you !

• FFMPEG converting media type aswell as relocating MOOV atom [migrated]

  11 juin 2013, par Samuel Richards

  I have found this line online

  ffmpeg -i input.mp4 -c:a copy -c:v copy -movflags faststart output.mp4

  Which takes an input, and copies the audio, video and sets the MOOV atom to the beginning in an element called output.mp4. Basically creating the same video with the MOOV atoms in a new place.

  I need to convert the type of this media though - so I have the line

  ffmpeg -i input.wmv -vcodec h264 -f mp4 output.mp4

  My problem is, is this possible in one line ? I know I can run one after another but that creates a couple of videos when I only need the resulting video, which could result in a lot of memory wasted.

  I am sure the line

  ffmpeg -i input.wmv -movflags faststart -vcodec h264 -f mp4 output.mp4 

  Is legitimate, but without the straight copies, this takes a long long time to compute.

  Any input on MOOV atoms and ffmpeg computation is welcome.

• How to record a video and create a file every 1 minute and without stopping media recorder as stopping and starting causing delay

  7 janvier 2021, par Karsh Soni

  I want to develop a functionality where i have to start recording or say start continuous recording for more than 5 hours and for every minute i want to create a video file so that i want to store files of a video every minute without any delay or missing any frame.

  


  Right now to create a file i need to stop the media recorder and which leads to stopping and starting media recorder and it ends up losing 1.5 to 3 seconds of delay based on devices where i want to minimize the delay as negligible as possible.

  


  I am getting callbacks or frames for each second but if i would try to save those bitmaps and then try to convert them into video it might work with 5FPS. but with 30 or 60FPS its not performing as continuous frames wouldn't let me write to files efficiently. even though that is being done in background.

  


  Please let me know if you know any alternate solution or any solution that can help me achieve it.