Is it permissible to watch videos and listen to them with added sound effects by the publisher, if their content is permissible, while not knowing if the producer of these effects authorized their publication?

Materials for which it is not known or highly probable from circumstantial evidence that they are copyrighted, there is no harm in benefiting from them without explicit permission. Therefore, there is no objection to watching videos that are permitted, even if they contain laments (aahat) for which permission is not known.