Fix #431 - convert gif to webm during upload. Web UI treats them like it did

before. In the API, attachments now can be either image, video or gifv. Gifv
is to be treated like images in terms of behaviour, but are videos by file
type.

app/models/media_attachment.rb

@@ -1,15 +1,32 @@
 # frozen_string_literal: true
 
 class MediaAttachment < ApplicationRecord
+  self.inheritance_column = nil
+
+  enum type: [:image, :gifv, :video]
+
   IMAGE_MIME_TYPES = ['image/jpeg', 'image/png', 'image/gif'].freeze
   VIDEO_MIME_TYPES = ['video/webm', 'video/mp4'].freeze
 
+  IMAGE_STYLES = { original: '1280x1280>', small: '400x400>' }.freeze
+  VIDEO_STYLES = {
+    small: {
+      convert_options: {
+        output: {
+          vf: 'scale=\'min(400\, iw):min(400\, ih)\':force_original_aspect_ratio=decrease',
+        },
+      },
+      format: 'png',
+      time: 0,
+    },
+  }.freeze
+
   belongs_to :account, inverse_of: :media_attachments
   belongs_to :status,  inverse_of: :media_attachments
 
   has_attached_file :file,
-                    styles: -> (f) { file_styles f },
-                    processors: -> (f) { f.video? ? [:transcoder] : [:thumbnail] },
+                    styles: ->(f) { file_styles f },
+                    processors: ->(f) { file_processors f },
                     convert_options: { all: '-quality 90 -strip' }
   validates_attachment_content_type :file, content_type: IMAGE_MIME_TYPES + VIDEO_MIME_TYPES
   validates_attachment_size :file, less_than: 8.megabytes
@@ -27,45 +44,45 @@ class MediaAttachment < ApplicationRecord
     self.file = URI.parse(url)
   end
 
-  def image?
-    IMAGE_MIME_TYPES.include? file_content_type
-  end
-
-  def video?
-    VIDEO_MIME_TYPES.include? file_content_type
-  end
-
-  def type
-    image? ? 'image' : 'video'
-  end
-
   def to_param
     shortcode
   end
 
   before_create :set_shortcode
+  before_post_process :set_type
 
   class << self
     private
 
     def file_styles(f)
-      if f.instance.image?
+      if f.instance.file_content_type == 'image/gif'
         {
-          original: '1280x1280>',
-          small: '400x400>',
-        }
-      else
-        {
-          small: {
+          small: IMAGE_STYLES[:small],
+          original: {
+            format: 'webm',
             convert_options: {
               output: {
-                vf: 'scale=\'min(400\, iw):min(400\, ih)\':force_original_aspect_ratio=decrease',
+                'c:v' => 'libvpx',
+                'crf' => 6,
+                'b:v' => '500K',
               },
             },
-            format: 'png',
-            time: 1,
           },
         }
+      elsif IMAGE_MIME_TYPES.include? f.instance.file_content_type
+        IMAGE_STYLES
+      else
+        VIDEO_STYLES
+      end
+    end
+
+    def file_processors(f)
+      if f.file_content_type == 'image/gif'
+        [:gif_transcoder]
+      elsif VIDEO_MIME_TYPES.include? f.file_content_type
+        [:transcoder]
+      else
+        [:thumbnail]
       end
     end
   end
@@ -80,4 +97,8 @@ class MediaAttachment < ApplicationRecord
       break if MediaAttachment.find_by(shortcode: shortcode).nil?
     end
   end
+
+  def set_type
+    self.type = VIDEO_MIME_TYPES.include?(file_content_type) ? :video : :image
+  end
 end