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• Correcting color cast with ffmpeg

  16 mai 2018, par Henry H

  I have two videos that have a pretty significant blue cast to them. I took some stills at the same time and I’m happy enough with the colors on those and I’d like to re-encode the videos, adjusting the colors to something similar to the stills.

  • A frame from the original video can be seen here : http://www.dotrose.com/temp/img_20180513_153484_original.png
  • An attempt at correcting the color, which would be acceptable : http://www.dotrose.com/temp/img_20180513_153484_corrected.png
  • A still image taken at the same time (but with some help from a flash) : http://www.dotrose.com/temp/img_20180513_153476.jpg

  I understand I could either create a large collection of jpg images from the video and color correct them before reassembling them into a new video or I could use ffmpeg’s color level’s filter to do it directly. What I don’t know is how to get the numbers to pass to the filter. I’m assuming I want to do something like this :

  ffmpeg -i video.mov -vf "colorlevels=rimin=##/255:gimin=##/255:bimin=#/255:rimax=###/255:gimax=###/255:bimax=###/255, eq=gamma=#.##" -y out.mov

  How do I get the values to use for each of the r, g, and b min and max settings and gamma to use in place of the ###s ? Assuming this is the right approach, of course.

  Update : Perhaps this question would be better asked in a forum for gimp or photoshop. But I know how to adjust the color in those. What I need to know is how I translate those changes to what ffmpeg is expecting.

• ffmpeg - zoompan causing stretching

  15 septembre 2020, par Sarmad S.

  I have two images as input, both are 1600x1066. I am vertically stacking them. Then I am drawing a box and vertically stacking that box under both of the image. Inside of the box I write text, then I output a video that is 1080x1920. Everything works well, until I use zoompan to zoom in on the images, I get a weird behavior (see images included below). basically all input images including the box stretchs (shrink) vertically and no longer fit the entire height of the video which is 1920.

  


  The command (removed some drawtext commands from it) :

  


  -filter_complex 
"color=s=1600x1066:color=blue, drawtext=fontfile=font.otf: text='My Text':fontcolor=white: fontsize=30: x=50: y=50[box]; 
[0]scale=4000x4000,zoompan=z='min(zoom+0.0015,1.5)':x='iw/2-(iw/zoom/2)':y='ih/2-(ih/zoom/2)':d=125:s=1600x1066[z0];
[1]scale=4000x4000,zoompan=z='min(zoom+0.0015,1.5)':x='iw/2-(iw/zoom/2)':y='ih/2-(ih/zoom/2)':d=125:s=1600x1066[z1];
[z0][z1][box]vstack=inputs=3"


  


  How do I fix this ? I want to zoom in without stretching the images.

  


  Video before using zoompan : https://i.stack.imgur.com/kTBto.jpg

  


  Video after using zoompan : https://i.stack.imgur.com/7faNn.png

  


• Best way to record a HTML Canvas/WebGL animation into a video on server ?

  19 juillet 2015, par Abhinav

  I have a set of animations which I can make in Canvas (fabric.js) or WebGL (three.js). I need to record them automatically through a script and output a video file.

  The animations include :
  1. Pictures
  2. Videos (with audio)
  3. Other animations/effects

  I have researched a lot during last few months on this.

  Results
  1. User PhantomJS + FFMPEG
  Run HTML Canvas animations on headless browser(PhantomJS) and record with FFMPEG. Here the issue is PhantomJS doesnot support neither WebGL nor Video element. http://phantomjs.org/supported-web-standards.html

  2. Use Websockets to send data back to server using DataURL
  Here again, we will need to run the animations on browser (which we cant because we have to do everything on server).

  3. Use node-canvas
  This is a library by TJ Holowaychuk which allows to render HTML Canvas on node.js. But it has its own limitations plus I haven’t really explored this field much.
  (If someone could shed more light on this library)

  If anyone has done it before or can guide me somewhere useful.
  All we need to do is use some data to create animations and record it into a video, everything on server side.