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• avcodec/nvdec : Add support for decoding monochrome av1

  6 décembre 2020, par Philip Langdale

  avcodec/nvdec : Add support for decoding monochrome av1
  The nvidia hardware explicitly supports decoding monochrome content,
  
  presumably for the AVIF alpha channel. Supporting this requires an
  
  adjustment in av1dec and explicit monochrome detection in nvdec.
  I'm not sure why the monochrome path in av1dec did what it did - it
  
  seems non-functional - YUV440P doesn't seem a logical pix_fmt for
  
  monochrome and conditioning on chroma sub-sampling doesn't make sense.
  
  So I changed it.
  I've tested 8bit content, but I haven't found a way to create a 10bit
  
  sample, so that path is untested for now.
  

  • [DH] libavcodec/av1dec.c
  • [DH] libavcodec/nvdec.c
  • [DH] libavcodec/version.h

• avcodec/aom_film_grain : implement AFGS1 parsing

  26 février 2024, par Niklas Haas

  avcodec/aom_film_grain : implement AFGS1 parsing
  Based on the AOMedia Film Grain Synthesis 1 (AFGS1) spec :
  
    https://aomediacodec.github.io/afgs1-spec/
  The parsing has been changed substantially relative to the AV1 film
  
  grain OBU. In particular :
  1. There is the possibility of maintaining multiple independent film
  
     grain parameter sets, and decoders/players are recommended to pick
  
     the one most appropriate for the intended display resolution. This
  
     could also be used to e.g. switch between different grain profiles
  
     without having to re-signal the appropriate coefficients.
  2. Supporting this, it's possible to *predict* the grain coefficients
  
     from previously signalled parameter sets, transmitting only the
  
     residual.
  3. When not predicting, the parameter sets are now stored as a series of
  
     increments, rather than being directly transmitted.
  4. There are several new AFGS1-exclusive fields.
  I placed this parser in its own file, rather than h2645_sei.c, since
  
  nothing in the generic AFGS1 film grain payload is specific to T.35, and
  
  to compartmentalize the code base.
  

  • [DH] libavcodec/aom_film_grain.c
  • [DH] libavcodec/aom_film_grain.h

• simple way te to compute rgb buffer from I420 frame ffmpeg

  9 mars 2023, par hacenesh

  I'm trying to compute directly rgb buffer from avframe. Something is going wrong since the obtained image is wrong. Extracting grey image from AVFrame->data[0] is working fine. However I'm not able to extract colored image

  


  inline void YCrCb_to_RGB8(int Y, int Cr, int Cb, int& R, int& G, int& B){

   R = (int)(Y + 1.402 *(Cr - 128));
   G = (int)(Y - 0.344136*(Cb-128) -0.71414*(Cr-128));
   B = (int)(Y + 1.772 *(Cb-128));

   if (R < 0) R = 0; else if (R > 255) R = 255;
   if (G < 0) G = 0; else if (G > 255) G = 255;
   if (B < 0) B = 0; else if (B > 255) B = 255;
}

int getRGB8buffer(AVFrame* pFrame, byte* buffer){

   const int width = pFrame->width, height = pFrame->height;
   int Y, Cr, Cb;
   int R, G, B;

   int pixel = 0;
   for (int y = 0; y < height; y++)
   {
    for (int x = 0; x < width; x++)
    {

        Y = pFrame->data[0][x + y * width];
        Cr = pFrame->data[1][x / 2 + ((int)(y / 2)) * pFrame->linesize[1]];
        Cb = pFrame->data[2][x / 2 + ((int)(y / 2)) * pFrame->linesize[2]];

        YCrCb_to_RGB8(Y, Cr, Cb, R, G, B);
        buffer[pixel * 3 + 0] = R;
        buffer[pixel * 3 + 1] = G;
        buffer[pixel * 3 + 2] = B;
        pixel++;
    }
   }
   return 0;
}


  


  When I save the obtained image as ppm using

  


  int save_RGB_frame(unsigned char* buf, int wrap, int xsize,int ysize, const char* filename){

   FILE* f;
   int i;
   f = fopen(filename, "w");
   // portable ppm format -> https://en.wikipedia.org/wiki/Netpbm#PPM_example
   fprintf(f, "P6\n%d %d\n%d\n", xsize, ysize, 255);

   // writing line by line
   for (i = 0; i < ysize; i++)
      fwrite(buf + i * wrap, 1, xsize*3, f);
   fclose(f);

   return 0;
 }


  


  The resulting image is wrong
link the the resulting image https://github.com/hacenesh/ffmpeg_question/blob/main/img_2028144.ppm