[Solved] How to make OpenCV to ask libv4l YUYV pixelformat instead of BGR24?

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I use at the moment OpenCV 2.4.4 on Linux Mint 14 (aka Ubuntu 12.10). I got 2 identical webcams (Logitech C270) and I need to run them simultaneously. From the start I want to say - using 2 USB hosts is not a solution for me. It is possible to run them simultaneously at 640x480@30 fps. But with one condition - use YUYV pixelformat. As all of us knows OpenCV uses BGR24 pixelformat. And here starts strange things... I am running v4l2-ctl -d /dev/video0 --list-formats and I get this:

    Index       : 0
    Type        : Video Capture
    Pixel Format: 'YUYV'
    Name        : YUV 4:2:2 (YUYV)

    Index       : 1
    Type        : Video Capture
    Pixel Format: 'MJPG' (compressed)
    Name        : MJPEG

As you can see we don't have here BGR24 pixelformat. For testing purposes I use qv4l2 application. It can list supported pixelformats and one of them is BGR24! How is that possible? Strange things continues... If I try BGR24 with qv4l2 (OpenCV force this one) I can't get higher than 15 fps for simultaneous running. How is that possible - call for unlisted pixelformat and get it?! The most strange thing - it gets it and USB host can't let through such a large datastream :\ This is weird because it means that v4l doesn't convert YUYV to BGR24, it just gets BGR24 from camera (???)! One the solution would be lowering fps, but I don't want to do that. As far as I know to achieve what I want I have to modify ./modules/highgui/src/cap_libv4l.cpp (cap_v4l.cpp doesn't play role, because it isn't even compiled). From the start I want to say - I am lame at programming. I made this changes:

1) I took from cap_v4l.cpp code which converts YUYV to RGB24:

/* convert from 4:2:2 YUYV interlaced to RGB24 */
/* based on ccvt_yuyv_bgr32() from camstream */
#define SAT(c) \
   if (c & (~255)) { if (c < 0) c = 0; else c = 255; }

static void
yuyv_to_rgb24 (int width, int height, unsigned char *src, unsigned char *dst)
{
   unsigned char *s;
   unsigned char *d;
   int l, c;
   int r, g, b, cr, cg, cb, y1, y2;

   l = height;
   s = src;
   d = dst;
   while (l--) {
      c = width >> 1;
      while (c--) {
         y1 = *s++;
         cb = ((*s - 128) * 454) >> 8;
         cg = (*s++ - 128) * 88;
         y2 = *s++;
         cr = ((*s - 128) * 359) >> 8;
         cg = (cg + (*s++ - 128) * 183) >> 8;

         r = y1 + cr;
         b = y1 + cb;
         g = y1 - cg;
         SAT(r);
         SAT(g);
         SAT(b);

     *d++ = b;
     *d++ = g;
     *d++ = r;

         r = y2 + cr;
         b = y2 + cb;
         g = y2 - cg;
         SAT(r);
         SAT(g);
         SAT(b);

     *d++ = b;
     *d++ = g;
     *d++ = r;
      }
   }
} 

2) Made OpenCV ask for YUYV instead BGR24 (here I show already modified code):

  /* libv4l will convert from any format to V4L2_PIX_FMT_YUYV */
  CLEAR (capture->form);
  capture->form.type                = V4L2_BUF_TYPE_VIDEO_CAPTURE;
  capture->form.fmt.pix.pixelformat = V4L2_PIX_FMT_YUYV;
  capture->form.fmt.pix.field       = V4L2_FIELD_ANY;
  capture->form.fmt.pix.width = capture->width;
  capture->form.fmt.pix.height = capture->height;
...
  if (V4L2_PIX_FMT_YUYV != capture->form.fmt.pix.pixelformat) {
      fprintf( stderr, "HIGHGUI ...