#351

backend/app/models/post.rb

@@ -46,6 +46,7 @@ class Post < ApplicationRecord
   before_validation :normalise_url
 
   validates :url, presence: true, uniqueness: true
+  validates :video_ms, numericality: { only_integer: true, greater_than: 0 }, allow_nil: true
 
   validate :validate_original_created_range
   validate :url_must_be_http_url
@@ -94,12 +95,16 @@ class Post < ApplicationRecord
     s = total_s % 60
     min = (total_s / 60) % 60
     h = total_s / 3_600
+    remainder_ms = ms % 1_000
 
-    if h.positive?
-      '%d:%02d:%02d' % [h, min, s]
-    else
-      '%d:%02d' % [min, s]
-    end
+    base =
+        if h.positive?
+          '%d:%02d:%02d' % [h, min, s]
+        else
+          '%d:%02d' % [min, s]
+        end
+
+    remainder_ms.positive? ? "#{ base }.#{ remainder_ms.to_s.rjust(3, '0') }" : base
   end
 
   def snapshot_parent_post_ids = parents.order(:id).pluck(:id)