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• Writing subtitles on a video on different time frames

  22 mars 2023, par sarveshsta

  I am trying to write subtitles on a video. The problem is , with cv2(opencv-python), I am unable to write text on different time frames , lets say for first two seconds I want "Hello", and for another 3 seconds the video will show "this is the introduction" and so on.

  


  My question is, how can I achieve this with opencv-python. The thing why I want to use cv2 only is it creates an object for that video and do not create a new file, and that is important for my project.

  


  If you guys have any idea how we can write subtitles on a video without creating another file, please do let me know.

  


  I also tried ffmpeg it worked absolutely fine for me and I used a .srt file for that, but again it was creating a new file and same happened with moviepy library so in any case if you could show me a way how can we overwrite the file in ffmpeg or moviepy, it would be very helpful.

  


  THANKS.

  


• OpenCV : FFMPEG : tag not found while writing video from images

  15 avril 2017, par Fahad Naeem

  I’m trying to write a video using images in Python and on Ubuntu 14.04 and getting the following error :

  OpenCV : FFMPEG : tag 0xffffffff/’����’ is not found (format ’mp4 / MP4
  (MPEG-4 Part 14)’)’

  The code I’m using is listed below.

  import cv2
  
  img = cv2.imread("image.png")
  
  height , width , layers =  img.shape
  
  video = cv2.VideoWriter('video.mp4',-1,1,(width,height))
  
  video.write(img)
  
  cv2.destroyAllWindows()
  
  video.release()

• Black overlay appears when merging a transparent video to another video

  13 juin 2012, par RakeshS

  This is what I have done so far :

  Command to create a transparent PNG image :

  convert -size 640x480 -background transparent -fill blue \
  
  -gravity South label:ROCK image1-0.png

  Command to create a transparent video :

  ffmpeg -loop 1 -f image2 -i image1-0.png -r 20 -vframes 100 \
  
  -vcodec png -pix_fmt bgra mov-1.mov

  (as per this post) - I expect this video to be a transparent video.

  Command to overlay a video with another :

  ffmpeg -i final-video.mov -sameq -ar 44100 \
  
  -vf "movie=mov-1.mov [logo];[in][logo] overlay=0:0 [out]" \
  
  -strict experimental final-video.mov

  Above commands works perfect and I have not faced any problem, but I don't get what I expect which is kinda watermarking effect, I want mov-1.mov to be transparent with final-video.mov.

  Questions :

  1. Is there any way to verify if the generated video is transparent ? other than merging ?
  2. Not sure why the above mov-1.mov is not transparent when it is merged with final-video.mov, any info to solve this problem would be great.

  Please help.