A completely free ringtone making software, really do not need to connect a computer, iPhone directly make ringtones.
Select video from album, automatically extract audio from video
Upload mp3 from PC to iPhone via http service
Accurate to 0.1 second audio clipping
Share ringtones to friends
"No need to connect to a computer, the iPhone makes ringtones directly" requires iOS 11 or later, use the "GarageBand" APP, and the production method is within the help page of the APP.