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• Does anybody have experience in embedding ffmpeg in a macOS application for the App Store ? Has anybody had his application rejected for this reason ?

  31 octobre 2020, par Alfonso Tesauro

  I am developing a tool for macOS that needs some basic audio editing, and the simplest way to achieve this is to embed ffmpeg in the application binary and call it with NSTask. Of course, I resigned ffmpeg with my identity and the entitlements to inherit the host application's sandbox. Has anybody tried this with success ? Any help is greatly appreciated. Thanks

  


• FFmpeg add caption to top of video like memes

  25 juin 2018, par Praveen Tamil

  I’m trying to add a top section to a video like we do for image memes. I’m using drawtext option for that but the text is wrapped in output video.

  Let’s say I have a video and I need to add the caption like this to the whole video. How can i achieve this ?

  Expected output
  

  Resulted output

  I use below command for above result

  ffmpeg -ss 20 -i  D:\21-03-2018\15271618235b06a3df9d5cb.mp4 -filter_complex "[0:v]pad=iw:ih+50:0:50:color=white, drawtext=text='Meme Top Text will go here but it\\\\\'s a long text with multi line option. Line 1 text \n line 2 text \n line 3 text':fix_bounds=true:fontfile=Arial.ttf:fontsize=30:fontcolor=black:x=(w-tw)/2:y=(50-th)/2" -vframes 1 D:\21-03-2018\output.jpg

• OpenCV Encoding to H264 changing original RGB pixel values for gray images

  13 janvier 2020, par CristoJV

  I have the following issue :
  I’m creating a uniform gray color video (for testing) using OpenCV VideoWriter. The output video will reproduce a constant image where all the pixels must have the same value x (25, 51, 76,... and so on).
  When I generate the video using MJPG Encoder :

  vw = cv2.VideoWriter('./videos/input/gray1.mp4',
  
          cv2.VideoWriter_fourcc(*'MJPG'),
  
          fps,(resolution[1],resolution[0]))

  and read the output using the VideoCapture class, everything just works fine. I got a frame array with all pixel values set to (25,51,76 and so on).
  However when I generate the video using HEV1 (H.265) or also H264 :

  vw = cv2.VideoWriter('./videos/input/gray1.mp4',
  
          cv2.VideoWriter_fourcc(*'HEV1'),
  
          fps,(resolution[1],resolution[0]))

  I run into the following issue. The frame I got in BGR format follows the next configuration :

  • The blue channel value is the expected value (x) minus 4 (25-4=21, 51-4=47, 76-4=72, and so on).
  • The green channel is the expected value (x) minus 1 (25-1=24, 51-1=50, 76-1=75).
  • The red channel is the expected value (x) minus 3 (25-3=22, 51-3=48, 76-3=73).

  Notice that the value is reduced with a constant value of 4,1,3, independently of the pixel value (so there is a constant effect).
  What I could explain is a pixel value dependable feature, instead of a fixed one.
  What is worse is that if I choose to generate a video with frames consisting in every color (pixel values [255 0 0],[0 255 0] and [0 0 255]) I get the corresponding outputs values ([251 0 0],[0 254 0] and [0 0 252])
  I though that this relation was related to the grayscale Y value, where :

  Y = 76/256 * RED + 150/256 * GREEN + 29/256 * BLUE

  But this coefficients are not related with the output obtained. Maybe the problem is the reading with VideoCapture ?

  EDIT :
  In case that I want to have the same output value for the pixels (Ej : [10,10,10] experimentally I have to create a img where the red and blue channel has the green channel value plus 2 :

  value = 10
  
  img = np.zeros((resolution[0],resolution[1],3),dtype=np.uint8)+value
  
      img[:,:,2]=img[:,:,2]+2
  
      img[:,:,1]=img[:,:,1]+0
  
      img[:,:,0]=img[:,:,0]+2

  Anyone has experience this issue ? It is related to the encoding process or just that OpenCV treats the image differently, prior encoding, depending on the fourcc parameter value ?