addresses #2499: Support uploading mp4 video

app/models/post.rb

@@ -153,10 +153,18 @@ class Post < ActiveRecord::Base
       file_ext =~ /swf/i
     end
 
-    def is_video?
+    def is_webm?
       file_ext =~ /webm/i
     end
 
+    def is_mp4?
+      file_ext =~ /mp4/i
+    end
+
+    def is_video?
+      is_webm? || is_mp4?
+    end
+
     def is_ugoira?
       file_ext =~ /zip/i
     end
@@ -620,10 +628,14 @@ class Post < ActiveRecord::Base
         tags << "flash"
       end
 
-      if is_video?
+      if is_webm?
         tags << "webm"
       end
 
+      if is_mp4?
+        tags << "mp4"
+      end
+
       if is_ugoira?
         tags << "ugoira"
       end