> Who via digital signature

the voice data signature can be removed, unless you mean something like an audio watermark

> What via hash

audio remuxing will destroy the hash, especially since it's already done by pretty much every social media company. Even with some sort of lossy audio hash, just put some clapping or cheering behind the voice and you've probably created a new audio hash.

> When via timestamp

file timestamps can change

This solves nothing unless your user either doesn't care about sharing the original file, or is malicious but too dumb to ffmpeg -i original.ogg out.mp3.