30-60 seconds is the industry standard. It’s a good idea to have versions at 15 seconds, 30 seconds, and 60 seconds. 90-second book trailers are also effective.
A book trailer is a video that’s similar to a movie trailer but for a book. However any sort of video that promotes a book or an author can be considered a book trailer.
Images that are connected to the plot and The themes of the book, snippets of scenes in cinematic form, a cinematic interview with the author, short blurb reviews woven into the video. These are just a few of the things to consider when producing a book trailer.