Currently, this extension does not appear to be supporting PostgreSQL natively, which is also discussed here. What happend for me was, that the update script did nothing to update my database and the upload afterwards complained about missing tables, guessing the update script had not been executed. Creating the transcode table and sequence manually with the correct permissions seems to have fixed the issue.
Imho this general issue is worth noting on the installation section for other users to at least know what they are getting into.