diff --git a/app/serializers/activitypub/note_serializer.rb b/app/serializers/activitypub/note_serializer.rb
index a8e1315bee..d67770933b 100644
--- a/app/serializers/activitypub/note_serializer.rb
+++ b/app/serializers/activitypub/note_serializer.rb
@@ -257,6 +257,7 @@ class ActivityPub::NoteSerializer < ActivityPub::Serializer
     attribute :focal_point, if: :focal_point?
     attribute :width, if: :width?
     attribute :height, if: :height?
+    attribute :duration, if: :duration?
 
     has_one :icon, serializer: ActivityPub::ImageSerializer, if: :thumbnail?
 
@@ -300,6 +301,10 @@ class ActivityPub::NoteSerializer < ActivityPub::Serializer
       object.file.meta&.dig('original', 'height').present?
     end
 
+    def duration?
+      object.file.meta&.dig('original', 'duration').present?
+    end
+
     def width
       object.file.meta.dig('original', 'width')
     end
@@ -307,6 +312,10 @@ class ActivityPub::NoteSerializer < ActivityPub::Serializer
     def height
       object.file.meta.dig('original', 'height')
     end
+
+    def duration
+      object.file.meta.dig('original', 'duration').seconds.iso8601
+    end
   end
 
   class MentionSerializer < ActivityPub::Serializer