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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.

• cliping a webm file using moviepy and ffmpeg parameters

  19 février 2015, par headdetective

  Using moviepy, I am trying to trim a section of a webm file like this :

  my_file.write_videofile(name, codec = 'libvpx')

  Of course, I have already defined the beginning and end of the clip, etc. The code is returning the segment I want, however, I am noticed a decrease in the quality of the file.
  I am not resizing or constraiing the file size anywhere, so I don’t understand why the clip has an inferior quality compared to the original.

  There are some parameters that I could play with, which I suspect are set as defaults in moviepy to speed of video manipulation, but the documentation of moviepy does not say anything about them :

  ffmpeg_params :

  Any additional ffmpeg parameters you would like to pass, as a list of
  terms, like [‘-option1’, ‘value1’, ‘-option2’, ‘value2’]

  Anybody outhere is familiar with the right parameters to keep the quality of the original file ? As an alternative, is anybody is familiar with any other library to trim webm files ?

  Below are two pics showing the difference in quality. The first one is a frame of the trimmed file, the second one is approximately the same frame, for the original file.

  

  

  Thank you

• How to map ffmpeg formats to MIME types and file extensions ?

  12 août 2020, par odigity

  Anyone know of a reference for mapping ffmpeg format values to MIME types and recommended file extension ? My google attempt failed to turn up anything.

  



  I did manually put together a small list with guess-work and clues from Wikipedia, IANA, and the Mozilla Developer Network for the subset of formats that I encountered in my video input test collection :

  



  ffmpeg Format             Extension  MIME Type
───────────────────────   ─────────  ────────────────────── 
asf                       asf        application/vnd.ms-asf
avi                       avi        video/x-msvideo
flv                       flv        video/x-flv
matroska,webm             webm       video/webm
m4v                       m4v        video/x-m4v
mov,mp4,m4a,3gp,3g2,mj2   mp4        video/mp4
mpeg                      mpeg       video/mpeg
mpegts                    mpeg       video/mpeg
mpegvideo                 mpeg       video/mpeg
ogg                       ogv        video/ogg
matroska                  mkv        video/x-matroska
webm                      webm       video/webm


  



  No idea if I've made the right calls, though.

  



  (The test files already have file extensions, but I'm operating on the assumption that the extension of a file a user uploads is irrelevant, and that the file should be renamed based on ffprobe and intelligent mapping...)