fallback to real filesize if approximate not available

pytube/extract.py

@@ -275,7 +275,7 @@ def apply_descrambler(stream_data: Dict, key: str) -> None:
                     "type": format_item["mimeType"],
                     "quality": format_item["quality"],
                     "itag": format_item["itag"],
-                    "bitrate": format_item["bitrate"],
+                    "bitrate": format_item.get("bitrate"),
                     "is_otf": (format_item.get("type") == otf_type),
                 }
                 for format_item in formats
@@ -291,7 +291,7 @@ def apply_descrambler(stream_data: Dict, key: str) -> None:
                     "type": format_item["mimeType"],
                     "quality": format_item["quality"],
                     "itag": format_item["itag"],
-                    "bitrate": format_item["bitrate"],
+                    "bitrate": format_item.get("bitrate"),
                     "is_otf": (format_item.get("type") == otf_type),
                 }
                 for i, format_item in enumerate(formats)

pytube/streams.py

@@ -164,9 +164,11 @@ class Stream:
         :rtype: int
         :returns: size of video in bytes
         """
-        assert self._monostate.duration is not None
-        bits_in_byte = 8
-        return int((self._monostate.duration * self.bitrate) / bits_in_byte)
+        if self._monostate.duration:
+            bits_in_byte = 8
+            return int((self._monostate.duration * self.bitrate) / bits_in_byte)
+        else:
+            return self.filesize
 
     @property
     def default_filename(self) -> str: