They're not reselling it nor redistributing it. The captions are derived from the AI and presented to the user. It may need some court precedent for this sort of thing, but I believe this would fall under "Fair Use".
Fair Use
Within copyright law there is a doctrine of law known as fair use. Although fair use does not actually give permission to make copies of a work or otherwise use a work without consent, the doctrine provides a defense to copyright infringement. The factors considered when applying the doctrine of fair use include: the purpose and character of the use, the nature of the copyrighted work, the amount of the work used, and the effect the use has upon the market for the copyrighted work.
Fair Use Within copyright law there is a doctrine of law known as fair use. Although fair use does not actually give permission to make copies of a work or otherwise use a work without consent, the doctrine provides a defense to copyright infringement. The factors considered when applying the doctrine of fair use include: the purpose and character of the use, the nature of the copyrighted work, the amount of the work used, and the effect the use has upon the market for the copyrighted work.