class ActiveStorage::Previewer::VideoPreviewer

def self.accept?(blob)
  blob.video?
end

def draw_relevant_frame_from(file, &block)
  draw ffmpeg_path, "-i", file.path, "-y", "-vcodec", "png",
    "-vf", "thumbnail", "-vframes", "1", "-f", "image2", "-", &block
end

def ffmpeg_path
  ActiveStorage.paths[:ffmpeg] || "ffmpeg"
end

def preview
  download_blob_to_tempfile do |input|
    draw_relevant_frame_from input do |output|
      yield io: output, filename: "#{blob.filename.base}.png", content_type: "image/png"
    end
  end
end