I mean, ffmpeg -i something.avi something.mp4 works as well, but there's just _so_ many more options inherently involved in converting a video: most input

I mean, ffmpeg -i something.avi something.mp4 works as well, but there's just _so_ many more options inherently involved in converting a video: most inputs and outputs will be at least 2 tracks, so that's 2 codecs, and the majority of containers used now (MP4, MKV, etc.) support all sorts of codecs, so while ffmpeg will "guess" what you want just like ImageMagick does in your short example, the chances that it guesses right are a lot lower just on the basic level of what format you wanted your output to be. But it's not exactly ffmpeg's fault.