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


i have been working rgb->yuv420 conversion sometime using ffmpeg library. tried sws_scale functionality not working well. now, have decided convert each pixel individually, using colorspace conversion formulae. so, following code gets me few frames , allows me access individual r,g,b values of each pixel:

// read frames , save first 5 frames disk     i=0;     while((av_read_frame(pformatctx, &packet)>=0) && (i<5))      {         // packet video stream?         if(packet.stream_index==videostreamidx)          {                /// decode video frame                         avcodec_decode_video2(pcodecctx, pframe, &framefinished, &packet);              // did 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 packet allocated av_read_frame         av_free_packet(&packet);     }

i read online convert rgb->yuv420 or vice-versa, 1 should first convert yuv444 format. so, like: rgb->yuv444->yuv420. how implement in c++?

also, here saveframe() function used above. guess have change little since yuv420 stores data differently. how 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; y<height; y++)         fwrite(pframe->data[0]+y*pframe->linesize[0], 1, width*3, pfile);      // close file     fclose(pfile); }

can please suggest? many thanks!!!

void saveframeyuv420p(avframe *pframe, int width, int height, int iframe) {     file *pfile;     char szfilename[32];     int  y;      // open file     sprintf(szfilename, "frame%d.yuv", iframe);     pfile=fopen(szfilename, "wb");     if(pfile==null)         return;      // write pixel data     fwrite(pframe->data[0], 1, width*height, pfile);     fwrite(pframe->data[1], 1, width*height/4, pfile);     fwrite(pframe->data[2], 1, width*height/4, pfile);      // close file     fclose(pfile); }

on windows, can use irfanview see frames saved way. open frame raw, 24bpp format, provide width , height, , check box "yuv420".


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