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• ffmpeg Cg shader ITU 709 YCbYg

  22 juillet 2018, par user2517097

  I have a viewer (mrViewer at sourceforge) that displays movie files by feeding YCbCr images and merging them later in a shader. Currently I am trying to track a color issue in my viewer, not displaying DNxHD movies properly. The EXR file is to be seen in RGB, not scene linear. The movie was created from that EXR file in Nuke (a comp program). All movie files are converted from EXR image without color space conversion in NUKE 11. All movie files are encoded with video color range.

  Color_Profile_nuke11.exr

  Color_Profile_nuke11_DNxHD_mov64_444.mov

  Color_Profile_nuke11_DNxHD_mov64_422.mov

  In the shader, I do (simplified Cg code) :

    half3 pre;
  
  
  
    pre.r = tex2D(YImage, tc).r;  // Y
  
    pre.g = tex2D(UImage, tc).r;  // U
  
    pre.b = tex2D(VImage, tc).r;  // V
  
  
  
    half3 c;
  
  
  
    if ( coeffs )
  
    {
  
        pre += Koff;
  
  
  
        c.r = dot(Kr, pre);
  
        c.g = dot(Kg, pre);
  
        c.b = dot(Kb, pre);
  
    }
  
    else
  
    {
  
  
  
        half3 yuv;
  
  
  
        yuv.r = 1.1643 * ( pre.r - 0.0625 );
  
        yuv.g = pre.g - 0.5;
  
        yuv.b = pre.b - 0.5;
  
  
  
        c.r = yuv.r + 1.5958 * yuv.b;
  
        c.g = yuv.r - 0.39173 * yuv.g - 0.81290 * yuv.b;
  
        c.b = yuv.r + 2.017 * yuv.g;
  
    }
  
  
  
    Out output;
  
    output.pixel = c;
  
    return output;
  
  
  
  
  
  
  
  // Send coeffs to shader shader (C++ code)
  
  {
  
  _shader->setUniform( "coeffs", 1 );
  
  // HDTV  YCbCr coefficients
  
  _shader->setUniform( "Koff", 0.0f, -0.5f, -0.5f );
  
  _shader->setUniform( "Kr", 1.0f, 0.0f, 1.28033f );
  
  _shader->setUniform( "Kg", 1.0f, -0.21482f, -0.38059f );
  
  _shader->setUniform( "Kb", 1.0f, 2.12798f, 0.0f );
  
  }

  Now, my problem is that the ITU 709 (the one with the dot() calls) path seems to not be behaving properly. It creates a washed out image. I am wondering if this has to do with full jpeg and full mpeg not having taken into account or whether my coefficients are wrong.

  If I set the color matrix to ITU709 in my C++ code with the ffmpeg library and let its swscale do the conversion, I get good color correspondence in the image if I select the (default) 601 path in the shader.

• Ffmpeg script cuts out sound

  15 février 2019, par Liam

  I have this ffmpeg script I’m running to automatically convert videos to instagram’s accepted coded

  The script looks like this :

  ffmpeg -analyzeduration 20M -probesize 20M -y -re -f lavfi -i "movie=filename='file.mp4':loop=5, setpts=N/(FRAME_RATE*TB)" -vcodec libx264 -b:v 3500k -vsync 2 -t 59 -acodec aac -b:a 128k -pix_fmt yuv420p -vf "scale=1080:1080:force_original_aspect_ratio=decrease,pad=1080:1080:(ow-iw)/2:(oh-ih)/2:white" -crf 24 new_file.mp4

  However that seems to cut out the audio, and I can’t seem to find out how to prevent that ? I didn’t use any -an or anything, and when messing around the audio keeps being cut out ? Any idea why ?

• Record Duet Video like Tiktok/Smule in flutter

  4 septembre 2021, par Mukund Jogi

  I am a newbie in Flutter. I am working on applications like Instagram/TikTok in which I am stuck with one issue that is Duet Video

  


  I have created Video Recording functionality using Img.ly SDK.

  


  I am also using FFmpeg library to give my own audio file to recorded video. But now I want to create functionality of Duet Video same as TikTok.

  


  Anyone can suggest a way to do it in Flutter ?