FFMPEG:RGB到YUV的转换通过二进制FFMPEG和代码C得到不同的结果

Question

我试图使用ffmpeg将RGB帧（ppm格式）转换为YUV420P格式。为了确保我的代码C是好的，我将输出与这个命令（同一个文件器BILINEAR）创建的输出进行了比较： ffmpeg-start_number1-i data/test512x512%d.ppm-sws_flags'bilinear'-pix_fmtyuv420p data/test-yuv420p.yuv

我的代码：

static unsigned char *readPPM(int i)
{
  FILE *pF;
  unsigned char *imgRGB;
  unsigned char *imgBGR;
  int w,h;
  int c;
  int bit;
  char buff[16];

  char *filename;
  asprintf(&filename,"test512x512%d.ppm",i);
  pF = fopen(filename,"rb");
  free(filename);

  if (pF) {
    if (!fgets(buff, sizeof(buff), pF)) {
      return nullptr;
    }
    if (buff[0] != 'P' || buff[1] != '6') {
      fprintf(stderr, "Invalid image format (must be 'P6')\n");
    return nullptr;
  }
  c = getc(pF);
  while (c == '#') {
    while (getc(pF) != '\n') ;
      c = getc(pF);
  }
  ungetc(c, pF);
  // read size
  if (fscanf(pF, "%d %d", &w, &h) != 2) {
    fprintf(stderr, "Invalid image size (error loading '%s')\n", filename);
    return nullptr;

  }
  //read bit
  if (fscanf(pF, "%d", &bit) != 1) {
    fprintf(stderr, "Invalid rgb component (error loading '%s')\n", filename);
    exit(1);
  }

  imgRGB =(unsigned char*) malloc(3*h*w);
  imgBGR =(unsigned char*) malloc(3*h*w);
  //read pixel data from file
  int length = fread(imgBGR, sizeof(unsigned char)*3, w*h, pF) ;
  if (length != w*h) {
    fprintf(stderr, "Error loading image '%s'\n", filename);
    return nullptr;
  }


  int start=0;
  for (i=0; i < HEIGHT*WIDTH;i++) {
   imgRGB[start] = imgBGR[start];
   imgRGB[start+2]= imgBGR[start+2];
   imgRGB[start+1]= imgBGR[start+1];
   start+=3;
  }

  fclose(pF);
  free(imgBGR);
  return imgRGB;
}
else {
  return nullptr;
}
}

void Test_FFMPEG::FillFrame (uint8_t* pic, int index)
{

 avpicture_fill((AVPicture*)RGBFrame, pic, AV_PIX_FMT_RGB24, encodeContext->width, encodeContext->height);

  struct SwsContext* fooContext = sws_getContext(encodeContext->width, encodeContext->height,
  PIX_FMT_RGB24,
  encodeContext->width, encodeContext->height,
  PIX_FMT_YUV420P,
  SWS_BILINEAR  , nullptr, nullptr, nullptr);
  sws_scale(fooContext, RGBFrame->data, RGBFrame->linesize, 0, encodeContext->height, OrgFrame->data, OrgFrame->linesize);

  OrgFrame->pts = index;
}

比较结果不好。在Y和V上有细微的差别，但在U上有很多差别。我不能发布我的图片，但Y的一部分在U图片中。它会使颜色有一点变化。

你能告诉我我的错误在哪里吗？谢谢

Answer 1

我不肯定ffmpeg的默认值，但是使用SWS_BILINEAR|SWS_ACCURATE_RND应该会产生更好的结果。