ffdshow already have resize to screen, but it add black bars. I already search the feature request and apparently there was a request like this already. Basically what I want is to resize the video to the nearest screen resolution. If I have 640/480 video, I want to resize it to 1400x1050 on 1680x1050 and not 1680x1050 with black bars on either sides. Using current ffdshow resize to screen resulted in subs not being placed correctly (since the subs expect a certain aspect ratio and didn't account for the added black bars by ffdshow) and since I set my media player (MPC-HC) to keep aspect ratio, then the black bars is counted as the movie resolution, thus the movie looked squashed.
You can overcome this limitation if at least ffdshow offer to resize by specifying vertical size (currently ffdshow can only have specify horizontal or specify both, but not specify only vertical) and make profile that is triggered by source aspect ratio.