#399

backend/app/services/post_import_previewer.rb

@@ -157,7 +157,15 @@ class PostImportPreviewer
 
   def initial_attributes row
     attributes = row[:attributes]&.stringify_keys || { }
-    FIELDS.to_h { |field| [field, attributes[field].to_s] }
+    FIELDS.to_h { |field|
+      value = attributes[field]
+      normalised =
+          if field == 'duration'
+            normalise_duration_attribute(value)
+          else
+            value.to_s
+          end
+      [field, normalised] }
   end
 
   def initial_provenance row
@@ -256,9 +264,20 @@ class PostImportPreviewer
   end
 
   def sanitise_metadata_duration value
-    return nil unless value.is_a?(Numeric)
+    return nil unless value.is_a?(String)
 
-    value.positive? ? value.to_i : nil
+    value.presence
+  end
+
+  def normalise_duration_attribute value
+    return '' if value.nil?
+    return value if value.is_a?(String)
+
+    milliseconds = Integer(value, exception: false)
+    return value.to_s if milliseconds.nil? || milliseconds <= 0
+
+    seconds_string = (milliseconds / 1_000.0).to_s
+    seconds_string.end_with?('.0') ? seconds_string.delete_suffix('.0') : seconds_string
   end
 
   def preload_metadata! prepared_rows, fetch_metadata, metadata_cache, existing_posts, url_counts
@@ -459,7 +478,7 @@ class PostImportPreviewer
   def parse_duration value, errors
     return nil if value.blank?
 
-    value.is_a?(Numeric) ? value.to_i : Tag.time_to_ms!(value.to_s, tag_name: '動画時間')
+    Tag.time_to_ms!(value.to_s, tag_name: '動画時間')
   rescue Tag::SectionLiteralParseError
     errors[:video_ms] = ['動画時間の記法が不正です．']
     nil