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• Convert individual pixel values from RGB to YUV420 and save the frame - C++

  24 mars 2014, par learner

  I have been working with RGB->YUV420 conversion for sometime using the FFmpeg library. Already tried the sws_scale functionality but its not working well. Now, I have decided to convert each pixel individually, using colorspace conversion formulae. So, following is the code that gets me few frames and allows me to access individual R,G,B values of each pixel :

  // Read frames and save first five frames to disk
  
      i=0;
  
      while((av_read_frame(pFormatCtx, &packet)>=0) && (i<5)) 
  
      {
  
          // Is this a packet from the video stream?
  
          if(packet.stream_index==videoStreamIdx) 
  
          {   
  
              /// Decode video frame            
  
              avcodec_decode_video2(pCodecCtx, pFrame, &frameFinished, &packet);
  
  
  
              // Did we get a video frame?
  
              if(frameFinished) 
  
              {
  
                  i++;
  
                  sws_scale(img_convert_ctx, (const uint8_t * const *)pFrame->data,
  
                            pFrame->linesize, 0, pCodecCtx->height,
  
                            pFrameRGB->data, pFrameRGB->linesize);
  
  
  
                  int x, y, R, G, B;
  
                  uint8_t *p = pFrameRGB->data[0];
  
                  for(y = 0; y < h; y++)
  
                  {  
  
                      for(x = 0; x < w; x++) 
  
                      {
  
                          R = *p++;
  
                          G = *p++;
  
                          B = *p++;
  
                          printf(" %d-%d-%d ",R,G,B);
  
                      }
  
                  }
  
  
  
                  SaveFrame(pFrameRGB, pCodecCtx->width, pCodecCtx->height, i);
  
              }
  
          }
  
  
  
          // Free the packet that was allocated by av_read_frame
  
          av_free_packet(&packet);
  
      }

  I read online that to convert RGB->YUV420 or vice-versa, one should first convert to YUV444 format. So, its like : RGB->YUV444->YUV420. How do I implement this in C++ ?

  Also, here is the SaveFrame() function used above. I guess this will also have to change a little since YUV420 stores data differently. How to take care of that ?

  void SaveFrame(AVFrame *pFrame, int width, int height, int iFrame)
  
  {
  
      FILE *pFile;
  
      char szFilename[32];
  
      int  y;
  
  
  
      // Open file
  
      sprintf(szFilename, "frame%d.ppm", iFrame);
  
      pFile=fopen(szFilename, "wb");
  
      if(pFile==NULL)
  
          return;
  
  
  
      // Write header
  
      fprintf(pFile, "P6\n%d %d\n255\n", width, height);
  
  
  
      // Write pixel data
  
      for(y=0; ydata[0]+y*pFrame->linesize[0], 1, width*3, pFile);
  
  
  
      // Close file
  
      fclose(pFile);
  
  }

  Can somebody please suggest ? Many thanks !!!

• arm : vp9mc : Load only 12 pixels in the 4 pixel wide horizontal filter

  3 janvier, par Janne Grunau

  arm : vp9mc : Load only 12 pixels in the 4 pixel wide horizontal filter
  This reduces the amount the horizontal filters read beyond the filter
  
  width to a consistent 1 pixel. The data is not used so this is usually
  
  not noticeable. It becomes a problem when the application allocates
  
  frame buffers only for the aligned picture size and the end of it is at
  
  a page boundary. This happens for picture sizes which are a multiple of
  
  the page size like 1280x640. The frame buffer allocation is based on
  
  its most likely done via mmap + MAP_ANONYMOUS so start and end of the
  
  buffer are page aligned and the previous and next page are not
  
  necessarily mapped.
  
  This mirrors the aarch64 change.
  Signed-off-by : Janne Grunau <janne-ffmpeg@jannau.net>
  
  Signed-off-by : Ronald S. Bultje <rsbultje@gmail.com>
  

  • [DH] libavcodec/arm/vp9mc_neon.S

• aarch64 : vp9mc : Load only 12 pixels in the 4 pixel wide horizontal filter

  3 janvier, par Janne Grunau

  aarch64 : vp9mc : Load only 12 pixels in the 4 pixel wide horizontal filter
  This reduces the amount the horizontal filters read beyond the filter
  
  width to a consistent 1 pixel. The data is not used so this is usually
  
  not noticeable. It becomes a problem when the application allocates
  
  frame buffers only for the aligned picture size and the end of it is at
  
  a page boundary. This happens for picture sizes which are a multiple of
  
  the page size like 1280x640. The frame buffer allocation is based on
  
  its most likely done via mmap + MAP_ANONYMOUS so start and end of the
  
  buffer are page aligned and the previous and next page are not
  
  necessarily mapped.
  
  Under these conditions like seen by Firefox a read beyond the end of the
  
  buffer results in a segfault.
  
  After the over-read is reduced to a single pixel it's reasonable to use
  
  VP9's emulated edge motion compensation for this.
  Fixes : https://bugzilla.mozilla.org/show_bug.cgi?id=1881185
  
  Signed-off-by : Janne Grunau <janne-ffmpeg@jannau.net>
  
  Signed-off-by : Ronald S. Bultje <rsbultje@gmail.com>
  

  • [DH] libavcodec/aarch64/vp9mc_neon.S