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• imagemagick gradient mask file creation

  6 avril 2016, par lang2

  I’m playing with this creative script here : http://www.fmwconcepts.com/imagemagick/transitions/. The plan is to mimic what happens with the script with ffmpeg and generate video with transition effects between pictures. My current understanding is this :

  1. I have two pictures A and B.
  2. I need in between a couple of pictures (say 15) that are partially A and partially B.
  3. To do that I use the composite -compose src-over A.jpg B.jpg mask-n.jpg out.jpg command.
  4. During the process, the mask-n.jpg gets generated automatically that gradually change from all black to all white.
  5. Depends on the mathematically equations, the way the transition effect looks is different.

  In one of the example, Fred the author gave this :

  convert -size 128x128 gradient: maskfile.jpg

  This will generate a image like this :
  

  This is partially black and partially white. For the transition to work, I’ll need an all white one and an all black one and a couple of others in between. What’s the magical command to do that ?

• ffmpeg : Generate empty audio and video (working for video)

  17 septembre 2021, par David Ferris

  I'm trying to generate a black video with FFMPEG. I have accomplished this with the following :

  


  ffmpeg -t 5 -f lavfi -i color=c=black:s=1920x1080 -c:v libx264 -tune stillimage -pix_fmt yuv420p out.mp4


  


  Unfortunately this video doesn't have any audio tracks. Following this, I have tried to insert -i anullsrc=channel_layout=stereo:sample_rate=44100 :

  


  ffmpeg -t 5 -i anullsrc=channel_layout=stereo:sample_rate=44100 -f lavfi -i color=c=black:s=1920x1080 -c:v libx264 -tune stillimage -pix_fmt yuv420p out.mp4


  


  Unfortunately this gives the error :

  


  


  anullsrc=channel_layout=stereo:sample_rate=44100 : No such file or
directory

  


  


  How can I modify my initial script to generate a video with empty audio ?

  


• ffmpeg : combine filter_complex trim, overlay and concat

  4 octobre 2015, par jb_alvarado

  I try to combine different video and audio clips with trimming and a logo on top.

  My syntax looks like this :

  ffmpeg -i "$introVid" -i "$introAud" -i "$mainVid" -i "$mainAud" -i "$outroVid" -i "$outroAud" -i "$logo" -i "$mainVid" -i "$mainAud" \
  
  -filter_complex \
  
  "[2:0]trim=0.4:60[trimV1]; \
  
   [3:0]atrim=0.4:60[trimA1]; \
  
   [trimV1][6:v]overlay=main_w-overlay_w-20:15,fade=in:s=2:d=0.5:alpha=1,fade=out:s=60:d=0.5:alpha=1[fade]; \
  
   [7:0]trim=60.2:72[trimV2]; [8:0]atrim=60.2:72[trimA2]; \
  
   [0:0] [1:0] [fade] [trimA1] [4:0] [5:0] [trimV2] [trimA2] concat=n=4:v=1:a=1[cv][a]; \
  
   [cv]scale=864:480:flags=gauss:interl=0[scal]" \
  
  -map "[scal]" -map "[a]" -pix_fmt yuv420p -c:v libx264 -preset fast -y "$out"

  It works mostly, but the problem is that I get a black video, with the same length then the main video, on the 3rd place. Interesting is also, when I watch the ffmpeg process, it hangs shortly on time 1:26min and then it jumps to 2:40min. Normally the complete test video have around 1:30min.

  The output what I get is at the moment :

  ([intro][trimmed main with logo][black video][outro][credits]) <- the black video part is to much.