We're using a modified version of the saMmapLoopback.c to test on our side. Most modifications affect our sensor configuration, and the only one regarding scaling is this addition:
{ struct v4l2_format fmt; struct v4l2_crop crop; /* Changing display window size to 200x200 */ fmt.type = V4L2_BUF_TYPE_VIDEO_OVERLAY; /*fmt.fmt.pix.width = display->width; fmt.fmt.pix.height = display->height; fmt.fmt.pix.pixelformat = DEF_PIX_FMT;*/ fmt.fmt.win.w.left = 0; fmt.fmt.win.w.top = 0; fmt.fmt.win.w.width = 720; fmt.fmt.win.w.height = 574; ret = ioctl(display->display_fd, VIDIOC_S_FMT, &fmt); if (ret < 0) { perror("VIDIOC_S_FMT\n"); goto ERROR; } crop.type = V4L2_BUF_TYPE_VIDEO_OUTPUT; crop.c.left = 0; crop.c.top = 0; crop.c.width = 1024; crop.c.height = 768; ret = ioctl(display->display_fd, VIDIOC_S_CROP, &crop); if (ret < 0) { perror("VIDIOC_S_CROP\n"); goto ERROR; } } We do it in display_prepare_streaming, right after:
fmt->fmt.pix.width = display->width; fmt->fmt.pix.height = display->height; fmt->fmt.pix.pixelformat = DEF_PIX_FMT; fmt->type = V4L2_BUF_TYPE_VIDEO_OUTPUT; ret = ioctl(display->display_fd, VIDIOC_S_FMT, fmt); if (ret < 0) { perror("VIDIOC_S_FMT"); goto ERROR; } I hope this helps.
Emilio.