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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.

• Resizing an mp4 with ffmpeg reduces color quality

  16 novembre 2019, par Jules

  Initially I’ve downloaded a video from an m3u8 to an mp4. The color of the downloaded video is fine at this point and mirrors the source. This is the command I’m using..

  ffmpeg -i https://...default.m3u8 -acodec copy -vcodec copy download.mp4

  My next step is to resize the source video from 1142 x 652, to create a new larger letter-box / pillar-box video of 1920 x 886

  ffmpeg -i download.mp4 -vf "scale=(iw*sar)*min(1920/(iw*sar)\,886/ih):ih*min(1920/(iw*sar)\,886/ih), 
  
    pad=1920:886:(1920-iw*min(1920/iw\,886/ih))/2:(886-ih*min(1920/iw\,886/ih))/2" resized.mp4

  However the color of the resized video is different, it could be that the amount of colours has been reduced, but that’s just a guess.

• avcodec/libkvazaar : Respect codec context color settings.

  2 octobre 2023, par John Mather

  avcodec/libkvazaar : Respect codec context color settings.
  This patch makes the libkvazaar encoder respect color settings that are
  
  present on the codec context, including color range, primaries, transfer
  
  function and colorspace.
  

  • [DH] libavcodec/libkvazaar.c