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• Why are the colors transposed in my webm thumbnails ?

  9 décembre 2022, par Peter Chaplin

  I have been using ffmpeg to generate webm files from png frames, and the webm files run ok in my video player, but the thumbnail colours appear transposed - blue replacing red, purple replacing orange, brown replacing green. I've also encountered issue uploading the webm to an image hosting site (which normally does support webms), though this might be an issue on their end.
I'm on Ubuntu 22.04.1 LTS

  


  Does anyone know what might be causing this, and how to fix it ? Or how to check whether the webm files are ok or corrupted ?

  


  *Edit : ok, here's a side-by-side comparison of the thumbnails that appear in my file explorer - mp4 on the left and webm on the right.
Both were generated from the same set of pngs, using the same command except with the filename extension changed.

  


  

  


  Specifically,

  


  ffmpeg -framerate 24 -i Panel2Humanized/frame%04d.png panel2humanskin.webm


  


  and

  


  ffmpeg -framerate 24 -i Panel2Humanized/frame%04d.png panel2humanskin.mp4


  


  Both look the same when opened with a video player. It looks like the mp4 thumbnail grabbed the 1st frame while the webm grabbed the last, but the colors should be the same in each. (The text-bubble in the top-left is yellow in the mp4).

  


  *Follow-up : Apparently my WebMs are being generated in GBRP (Green-Blue-Red Planar) pixel format, the site I was trying to upload to requires YUV420P (Luma/Chroma 4:2:0 Planar) format, maybe that's the issue ? I'm still not sure exactly what that means or how to fix it.

  


  *Final follow-up : Looks like I needed to change the argument to :

  


  ffmpeg -framerate 24 -i Panel2Humanized/frame%04d.png -pix_fmt yuv420p paned2humanskin.webm


  


• ffmpeg : 1 frame manipulation on demand

  7 juillet 2013, par Chris Russo

  Hello folks & friends of SO !

  We need to create a small application to take a random frame from a video, and apply some modifications to it, in real time.

  This has to be done in real time, and in order to do that, we wouldn't mind to create some initial delay, before the video starts streaming. So let's assume we have a total of 6 seconds of preloading time, in order to :

  1) extract a keyframe.
  
  2) create an image with it.
  
  3) manipulate the image.
  
  4) replace the original keyframe with the new one.

  The point (3) of the previous algorithm is already solved using GD as a PHP module. However we would need to find a solution for the rest of the procedure in order to accomplish this.

  Please if anyone is available to help us with this, feel free to contact me.

  Thanks in advance ;
  Chris C. Russo

• Avoid caching files inside web folder

  14 octobre 2019, par JoakDA

  I have a real time application working with Symfony 4 and ffmpeg. It works great in development environment, but it hangs on production because the cache.

  Through ffmpeg, I write a mpd file from a RTSP stream in my /public/build/video folder.

  I need to avoid caching this mpd because it always changes while the real time video is displayed (ffmpeg is running on background).

  Please, could you help me to exclude "/public/build/video" folder and its content to be cachable.

  Find attached a screenshot :

  

  Thanks