How about create an audio editor by using fmod api?

Is this legal?
How to do it?
What should i do?
What should i pay attention to?

Creating any software that uses FMOD, whether it’s a game or an audio editor, requires an appropriate licence. See for information about the various licences we offer.

That said, the FMOD Studio programmer’s API isn’t suitable for creating most kinds of audio editing software. FMOD Studio is designed to produce dynamic audio content, while most audio editors need to produce linear audio files; While both are audio, the format and utility of the two types of output are completely different.

It may be possible to use the FMOD Studio programmer’s API to create an audio editor, but it’s not designed for that; You’d be fighting against the design the whole way, and there’s very little useful advice we’d be able to give you. I strongly recommend using some other API, or developing your own from scratch.