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• Converting 6 audio channels to 2 in ffmpeg

  12 juin 2013, par k1lljoy

  Im doing a 2 pass encode on the uploads to my site.

  Unfortunately when a user uploads a 6 audio channel .mkv files (5.1 surround), ffmpeg spits out the following error :

  Resampling with input channels greater than 2 unsupported.

  Im running the latest version of ffmpeg. Doing -ac 6 instead of the usual - ac 2 proceeds with the encoding, but it just creates a larger file with useless data, as well as creates another step in the already long file processing script, and I'd rather avoid modifying the conversion command.

  Is there anything I can do to make -ac 2 actually work ?

• How can I simply replace the colors using the color masks on this image and then save it ? With RGBA channels as example

  31 août 2020, par karl-police

  So I got this GIF here :

  


  

  


  As you can see, it has Red, Green and Blue in it. And it also has a full transparency in it. This was composed together with FFMPEG out of images that looked exactly like that.

  


   

  


  Then, with FFMPEG I "decomposed" the RGB and Alpha channels using the filter "extractplanes".

  


  The gallery of that, in correct order starting from up to down, can be found here :

  


  https://imgur.com/a/WN0aGuW

  


  I am not sure if this actually helps me or if I'm supposed to decompose them. Because apperantly now, after decomposing them, I'm supposed to modify them, but I'm not really sure how. It's like how do I modify the red channel that only has black and white, so all at the end, will match to the specified HEX color that I want it to be to.

  


   

  


  Now, my question is. How do I exactly make the color changing happen ? Can I do this simply with JavaScript ? Is it possible to do with FFMPEG, if possible without ImageMagicks ? Maybe a programming language where not much installation is needed to do that ?

  


  What I understood is that. These channels basically contain values from 0 to 255 with black and white. I think the "brightness" is that what 0 and 255. So something inbetween, would be like grey.

  


  So basically, like we do (255,0,0) for red. In these channels, if I want red somewhere I need to put one fully white pixel on the red channel and on all the other channels, there has to be a fully black pixel.

  


  That's the concept. Now is the question, how can I do this ?

  


   

  


  At the end I want to make it look like the colors this one has, as example :

  


  

  


  This is from a game. So basically that's how it looks like in the game. And the game files only use these RGBA template sprites.

  


   

  


  I asked a similar question here : How to change colors of an image using RGBA and more channels independently of their color

  


  But somehow, I might didn't seem to explain it that well.

  


   

  


  I made a thing here to test around with things. I guess that's nearly close, but the lines are kinda weird. jsfiddle.net/qsgazubk

  


• Youtube dl for python : set mp3 last modif date date

  24 janvier 2021, par Vladimir Tarasov

  I'm using Youtube-dl (and ffmpeg) in a python project.

  


  The problem I have is that, on download, the downloaded file takes as default the youtube's release date of the video instead of the download date.

  


  My youtube-dl options

  


  ydl_opts = {
    'format': 'bestaudio/best',
    'outtmpl': path + urlToTitleYT(link) + '.mp3',
    'postprocessors': [{
        'key': 'FFmpegExtractAudio',
        'preferredcodec': 'mp3',
        'preferredquality': '320',
    }],
}


  


  Which opt could i use in order to change the file last modification date to the download date ?
(Or do i have to edit it manually ?)