Interestingly, a service that made that use-case into a turn-key and repeatable API call would probably be quite profitable. The target market would be web marketers and social media managers who have to pump out content.

I'm imagining something like: upload a video without sound and the service would generate the exact amount of music necessary. Bonus points if you can get the music to loop seamlessly. Perhaps upload an image or series of images + text and the video would be ffmpeg'd together at a specified duration along with the generated music. Add some integration to manage the uploading to Instagram/TikTok/Facebook/etc.

It reminds me of a business I saw launched here that was an API to remove backgrounds from images. I didn't think such a service would be profitable but apparently there are enough people generating product photos for online stores that will throw money at such a service.