module ActiveStorage::Blob::Representable

whether a blob is accepted by any previewer, call ActiveStorage::Blob#previewable?.
This method raises ActiveStorage::UnpreviewableError if no previewer accepts the receiving blob. To determine

<%= image_tag video.preview(resize_to_limit: [100, 100]) %>

how to use the built-in version:
Active Storage provides one, but you may want to create your own (for example, if you need authentication). Here’s
Avoid processing previews synchronously in views. Instead, link to a controller action that processes them on demand.

blob.preview(resize_to_limit: [100, 100]).processed.url

extracts the first frame from a video and the PDF previewer extracts the first page from a PDF document.
from a non-image blob. Active Storage comes with built-in previewers for videos and PDF documents. The video previewer
Returns an ActiveStorage::Preview instance with the set of +transformations+ provided. A preview is an image generated

def preview(transformations)
  if previewable?
    ActiveStorage::Preview.new(self, transformations)
  else
    raise ActiveStorage::UnpreviewableError
  end
end