handle duration: N/A from ffprobe

feed

@@ -380,7 +380,10 @@ def get_duration(url):
         raise DurationNotFound(url) from exc
     duration = next(l for l in lineout if l.startswith(b"duration="))
     value = duration.split(b"=")[1]
+    try:
         return int(float(value))
+    except ValueError as exc:
+        raise DurationNotFound(url) from exc
 
 
 HELP = """