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• blank transparent pngs behave like black canvas

  10 novembre 2015, par Anay Bose

  I am trying to create a scrolling image with imagemagick’s roll and crop functions. Its a frame-by—frame animation. The source image is a transparent png with some text written on it. The following code works and it creates the required frames, including some blank png images at first for a nice, smooth effect. These blank pngs are what creating problems when I am trying to convert my image frames into video with ffmpeg. FFMPEG is seemingly considering these blank pngs as black/dark images, so the resulting video contains a blackout for a few seconds in the beginning—which I do not want.

  I am using png codec with bgra pixel format. My ffmpeg command (shown below) creates smooth, clear animation with images that have some text on it.

  "ffmpeg -i trans/trans-%d.png -vcodec png -pix_fmt bgra overlay-0.mov";

  The blank pngs behave like black canvas, but as I try to write some text on them or surround them with a border (i.e. colorize in some way) the problem disappears—which seems very strange. I have tested all my images ; they are all transparent. For the past few hours, I have been searching for a solution, no luck so far. Please note those blank pngs are required in the beginning for a smooth effect, and I cannot omit them. I have uploaded a sample video in Youtube. Please note the black fade out.

  https://www.youtube.com/watch?v=Te3LuItxcDk&feature=youtu.be

  https://youtu.be/Te3LuItxcDk

  PHP code :

     $increment = 40;
  
     $count = 0; 
  
  
  
     for ($x=40; $x <= 640 ; $x+=$increment) 
  
     {
  
       $roll = new Imagick(DOCROOT . '/composite-0.png');
  
       $roll->rollImage($x, 0);
  
       $roll->writeImage(DOCROOT . '/roll/roll-' . $x . '.png');
  
  
  
      $crop = new Imagick(DOCROOT . '/roll/roll-' . $x . '.png');
  
      $crop->cropImage($x, 720, 0, 0);
  
      $crop->writeImage(DOCROOT . '/roll/crop-' . $x . '.png');
  
  
  
      $extent = new Imagick(DOCROOT . '/roll/crop-' . $x . '.png'); 
  
      # $extent->setImageBackgroundColor(new ImagickPixel('none'));
  
      $extent->setImageBackgroundColor(new ImagickPixel('transparent'));
  
      $extent->extentImage(640, $extent->getImageHeight(), 0, 0);
  
      $extent->setImageFormat('png'); 
  
      $extent->writeImage(DOCROOT . '/trans/trans-' . $count . '.png');
  
  
  
      $count++; 
  
     }

• Fill output video with black screen in case of missing the input stream or switch input UDP stream to another source

  13 mai 2018, par Omar Mahmoud

  I am using FFMPEG to record a streams from UDP sources, but unfortunately once the input stream missed, the ffmpeg stop recording, then append video to file once the stream observed by the server again.

  And as these recording files is time based so, I need fill video with black screen in case of missing the input stream.

  ffmpeg -i ’udp ://224.12.12.1:4000’ -t 00:45:00 -vcodec copy -acodec copy -f mpegts /record/eEs1526947.ts

  How can I do this, either by ffmpeg or other CLI based service/process ?

• How to crop bottom of video followed by removing black borders ?

  9 mai 2018, par pmdaly

  I have video where there is a static bar on the bottom 50 pixels and also a black boarder around the actual content. I want to remove the bottom 50 pixels then use cropdetect to auto trim the border.

  I have the following to remove the border

  dims = $(ffmpeg -i "$video$ -t 1 -vf cropdetect -f null - 2>&1 | awk '/crop/{print $NF}' | tail -n1)
  
  
  
  ffmpeg -i "$video" -vf "$dims" "$video_out"

  I’m not sure how to add the step to remove the bottom 50 pixels prior to this.