From time to time I got the need to trim intros/outros or silence from downloaded audio files.
I’m currently using Super Sound, but I find it a little silly that one of the last closed source, filled with ads app I still have installed is for such a small functionality.
On desktop I use ffmpeg for pretty much anything, so if there is some wrapper for it over android it would be ideal.
Audacity used to be open source, several forks of it exist but easy to just download the last open source version of audacity (most Linux package managers will use this by default).