Yes, there's a thousand ways to detect the beat and interpret that as a tempo. If
there's a beat to detect.
Apologies if I was wrong, but my interpretation of the question, (and it is a fairly common snag), where we have a sound or track that lacks the detectable signature of a beat, and therefore creates a challenge that the common beat detection methods do not offer a solution for.....
"Guitar riff." Generally speaking, unless it is a pretty obvious choppy shuffle or some other rhythm track,(And often, perhaps even then) isn't going to work in beat detective, warping or any other automated solution I am aware of, thus my answer.
Again, if my assumption was incorrect, apologies.
Of course the real correct answer was perhaps, "record to a click or drum track." But the question was posed after that horse done fled the barn.
And anyway, pointing that out would be a job for.......