这个缩放比例怎么理解？
target_width_y = ((roi_w - 1) * 64 / (64 + factor) +1 >> 1) << 1
target_height_y = ((roi_h - 1) * 64 / (64 + factor) +1 >> 1) << 1
target_width_uv = ((roi_w /2 - 1) * 64 / (64 + factor) +1 >> 1) << 1
target_height_uv = (((roi_h /2 - 1) * 64 / (64 + factor) +1 >> 1) << 1