I like it, light and easy to use
I had troubles when using the crop syntax of Avisynth + resize though, I got only a distorted top of the image at the end.
And also a suggestion: let us choose the format of the output, raw h264 or MKV or MP4. It would be nice to have the audio muxed as well since you are using MKVmerge it shouldn't be hard to do. And you could also use MP4Box for muxing video + audio in MP4