Fixes rounding in seconds to tc conversion

src/main/python/ttconv/time_code.py

@@ -97,12 +97,12 @@ def parse(time_code: str) -> ClockTime:
 
   @staticmethod
   def from_seconds(seconds: Union[float, Fraction]) -> ClockTime:
-    """Creates a time code from time offset in seconds"""
+    """Creates a time code from time offset in seconds (rounds to the closest millisecond)"""
 
     if seconds < 0:
       raise ValueError("Seconds must not be less than zero")
 
-    seconds = float(seconds)
+    seconds = round(seconds, 3)
 
     h = floor(seconds / 3600)
     m = floor(seconds / 60 % 60)

src/test/python/test_time_code.py

@@ -66,5 +66,22 @@ def test_time_code(self):
     self.assertEqual("24:00:01,500", str(time_code))
     self.assertEqual(seconds, time_code.to_seconds())
 
+  def test_from_seconds_rounding_up(self):
+      seconds = Fraction(41039999,7500)
+      time_code = ClockTime.from_seconds(seconds)
+      self.assertEqual(time_code.get_hours(), 1)
+      self.assertEqual(time_code.get_minutes(), 31)
+      self.assertEqual(time_code.get_seconds(), 12)
+      self.assertEqual(time_code.get_milliseconds(), 0)
+
+
+  def test_from_seconds_rounding_down(self):
+      seconds = 5471.9994
+      time_code = ClockTime.from_seconds(seconds)
+      self.assertEqual(time_code.get_hours(), 1)
+      self.assertEqual(time_code.get_minutes(), 31)
+      self.assertEqual(time_code.get_seconds(), 11)
+      self.assertEqual(time_code.get_milliseconds(), 999)
+
 if __name__ == '__main__':
   unittest.main()