Check average_rate availability in video reader (#8548)

Co-authored-by: Nicolas Hug <[email protected]>
Co-authored-by: Nicolas Hug <[email protected]>

Author: stefan-baumann

torchvision/io/video_reader.py

@@ -251,7 +251,7 @@ def get_metadata(self) -> Dict[str, Any]:
                         rate_n = "framerate"
                     metadata[stream.type] = {rate_n: [], "duration": []}
 
-                rate = stream.average_rate if stream.average_rate is not None else stream.sample_rate
+                rate = getattr(stream, "average_rate", None) or stream.sample_rate
 
                 metadata[stream.type]["duration"].append(float(stream.duration * stream.time_base))
                 metadata[stream.type][rate_n].append(float(rate))