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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++; 
  
     }

• Live streaming HLS via ffmpeg, How to force client to start playing from the beginning ? From 1st segment

  12 mars 2015, par vedeojunky

  Is there a way, maybe via an ffmpeg option or flag, to force the client player to always start the playlist from the beginning when live streaming rather than the real time mid-stream ?

  Say the user comes in 1mn after the stream has started, rather than starting to watch at 1mn the player would start at the beginning of the video so minute zero.

  Here is my ffmpeg command :

  ffmpeg -f "screen capture" -s 1280x720 -r 30 -i :0.0+nomouse -f alsa -ac 2 -i pulse -async 30 -vcodec libx264 -pix_fmt yuv420p -acodec libfdk_aac -ar 44100 -b:a 64k -threads 0 -s 640x360 -f hls -g 1 -hls_time 1 -hls_list_size 1 -hls_allow_cache 0 /hls/#{@stream_name}/index.m3u8

  Thanks !

• ffmepg Low latency destkop mirroring with quicksync

  21 février 2016, par Alan Aasmaa

  I have tried to figure out long time how can i stream my Main PC to Secondary PC.

  I’d like to use QuickSync or NVENC
  https://github.com/illuspas/ffmpeg-hw-win32 ?

  I found something like this.
  ffmpeg \
  -f x11grab -s 1280x720 -framerate 60 -i :0.0 \
  -c:v mpeg2video -q:v 20 -pix_fmt yuv420p -g 1 -threads 2 \
  -f mpegts - | nc -l -p 9000

  I know x11grab is for linux so i should use dshow ?

  What would be best client to watch this ? I need also low CPU usage.

  Right now i got best latency 0.5sec by Streaming with action and reciving with vMix (I use vMix becose i stream back into OBS).

  My purpose is to Get CSGO from one PC to another and do a PiP stream. I don’t have capturecard and i dont have streaming PC. Also i don’t have money to buy neither of these.