It really do nothing as you can see - just get video and audio, put them together and return. But I get error "No video or audio found in media". So something is wrong. Maybe I should use something else instead of ffms2 for loading?
I think the best way to learn the basics of AviSynth is not to start with FFAStrans. Just like creating custom ffmpeg presets demands that you have some knowledge og ffmpeg, creating a custom AviSynth demand you have some knowledge of AviSynth.