There is no enforced maximum length for either input or output right now. In practice, the remote machine times out trying to analyze a song after 10 or so minutes. For output, your machine will take forever to generate really long results.
I had forgotten about this check actually! I just removed it and deployed the changes. You can try again but am unsure if it will break something (it will spin indefinitely, but I would give it up to 10 minutes). Good luck!