docs: add remaining docs for classes in app/logical.

app/logical/media_file/image.rb

@@ -1,3 +1,7 @@
+# A MediaFile for a JPEG, PNG, or GIF file. Uses libvips for resizing images.
+#
+# @see https://github.com/libvips/ruby-vips
+# @see https://libvips.github.io/libvips/API/current
 class MediaFile::Image < MediaFile
   # Taken from ArgyllCMS 2.0.0 (see also: https://ninedegreesbelow.com/photography/srgb-profile-comparison.html)
   SRGB_PROFILE = "#{Rails.root}/config/sRGB.icm"
@@ -31,8 +35,8 @@ class MediaFile::Image < MediaFile
     is_animated_gif? || is_animated_png?
   end
 
-  # https://github.com/jcupitt/libvips/wiki/HOWTO----Image-shrinking
-  # http://jcupitt.github.io/libvips/API/current/Using-vipsthumbnail.md.html
+  # @see https://github.com/jcupitt/libvips/wiki/HOWTO----Image-shrinking
+  # @see http://jcupitt.github.io/libvips/API/current/Using-vipsthumbnail.md.html
   def preview(width, height)
     output_file = Tempfile.new(["image-preview", ".jpg"])
     resized_image = image.thumbnail_image(width, height: height, **THUMBNAIL_OPTIONS)
@@ -62,6 +66,7 @@ class MediaFile::Image < MediaFile
     file_ext == :png && APNGInspector.new(file.path).inspect!.animated?
   end
 
+  # @return [Vips::Image] the Vips image object for the file
   def image
     Vips::Image.new_from_file(file.path, fail: true)
   end

app/logical/media_file/ugoira.rb

@@ -1,3 +1,10 @@
+# A MediaFile for a Pixiv ugoira file.
+#
+# A Pixiv ugoira is an animation format that consists of a zip file containing
+# JPEG or PNG images, one per frame, plus a JSON object containing the
+# inter-frame delay timings. Each frame can have a different delay, therefore
+# ugoiras can have a variable framerate. The frame data isn't stored inside the
+# zip file, so it must be passed around separately.
 class MediaFile::Ugoira < MediaFile
   class Error < StandardError; end
   attr_reader :frame_data
@@ -25,6 +32,7 @@ class MediaFile::Ugoira < MediaFile
     preview_frame.crop(width, height)
   end
 
+  # Convert a ugoira to a webm.
   # XXX should take width and height and resize image
   def convert
     raise NotImplementedError, "can't convert ugoira to webm: ffmpeg or mkvmerge not installed" unless self.class.videos_enabled?

app/logical/media_file/video.rb

@@ -1,3 +1,7 @@
+# A MediaFile for a webm or mp4 video. Uses ffmpeg to generate preview
+# thumbnails.
+#
+# @see https://github.com/streamio/streamio-ffmpeg
 class MediaFile::Video < MediaFile
   def dimensions
     [video.width, video.height]