Mainly I'm talking about audio based evidences.

Obviously, If you hear spirit box then it counts, but what about Ghost Writing and EMF.

When the ghost writes in the book, a certain audio plays. If you don't ever see the book written in, but instead hear the scribbles, would it count?

EMF Too. There is a pitch it plays when it hits EMF 5. This would be tricky to confirm though, so what about this: You see the EMF hit 4, then while it's out of view, you clearly hear the pitch go up, only meaning that it has hit EMF 5. Would that count as evidence?

I know these are stupid situations, but I found it as a gray area in the rules, seeing as the rules say "All evidences is required to be seen on the recording" however audio instead of visual is acceptable for the spirit box.

Hope anyone can clarify this for me, thanks.

If the audio cue is obvious enough, it counts as an evidence. You're right, it's not clear in the rule.

But in most cases, just try to have as much as visual witness as possible and your run should be valid.