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• How to capture device input with ffmpeg in C ?

  24 mai 2019, par Yi Lin Liu

  I am trying to use ffmpeg in my C code to capture device input, like screen and audio record. I have looked through their official documentation and wiki, but the API documentation is not really well explained compare to the command line usage.

  According to the documentation, if I want to record audio with alsa on linux I could, for example

  ffmpeg -f alsa -i hw:&lt;#card>,&lt;#device> -t <seconds> out.wav
  
  </seconds>

  I want to use the C API to do the same thing, any idea ?

• Restream an MJPEG from Axis IP Camera

  4 avril 2015, par FoleyX90

  Basically we have an IP camera set up offsite and we want people to be able to access the camera’s stream. Instead of everybody hitting the camera directly though, I need to our server to be able to grab the camera’s stream and distribute that to the users on the website. That way, there’s only 1 connection to the camera but we can handle many connections on our server. What tools should I use for this ? I’m very experienced in PHP and have some experience in FFMPEG but I can’t seem to find the right solution.

• FFMPEG blending comes out looking grayscale rather than colourful

  17 novembre 2022, par OneWorld

  When i do a blend of two pngs, it comes out looking grayscale whereas it should have colour.

  


  These are the two PNG input assets that I then create MP4s from :-

  


  

  


  

  


  Here is the command :-

  


  ffmpeg -i black_circle.png -i pikachu.png -filter_complex "[0:v]setsar=sar=1,format=rgb24[rgb1];[1:v]setsar=sar=1,format=rgb24[rgb2];[rgb1]split[out1_1][out1_2];[out1_1]crop=50:50:0:0:exact=1,setsar=1[cropped1];[cropped1][rgb2]blend=screen[blended1];[out1_2][blended1]overlay=0:0" pikachu_screened_on_circle_rgb.png


  


  And here is the output :-

  


  

  


  However, Pikachu should retain his Red, Green and Blue, but instead Pikachu looks grayscale.

  


  I was wondering why this is ?

  


  And what i need to do so that Pikachu retains his yellow skin, and rosey cheeks ?

  


  So I thought initially that it might be something to do with the white and black circle being a grayscale asset. But then I replaced the black and white circle with this asset :-

  


  

  


  and I saw that when something is black FFMPEG makes it grayscale :-

  


  

  


  The command using these two assets instead is this :-

  


  ffmpeg -i rgb_backing.png -i pikachu.png -filter_complex "[0:v]setsar=sar=1,format=rgb24[rgb1];[1:v]setsar=sar=1,format=rgb24[rgb2];[rgb1]split[out1_1][out1_2];[out1_1]crop=50:50:0:0:exact=1,setsar=1[cropped1];[cropped1][rgb2]blend=screen[blended1];[out1_2][blended1]overlay=0:0" pikachu_screened_on_rgb_backing.png


  


  Is there a way to invert black to white in FFMPEG ?