class ActiveStorage::Attachment

def preview(transformations)

unknown pre-defined variant of the attachment.
Raises an +ArgumentError+ if +transformations+ is a +Symbol+ which is an

See ActiveStorage::Blob::Representable#preview for more information.

video.preview(:thumb).processed.url

or if you are using pre-defined variants:

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

Example:
of +transformations+ provided.
Returns an ActiveStorage::Preview instance for the attachment with the set 
def preview(transformations)
  transformations = transformations_by_name(transformations)
  blob.preview(transformations)
end