podcast: better support for mRSS

they were already supported, but the duration tag was missed.
Now we look inside media:group, if available.

larigira/audiogen_podcast.py

@@ -121,9 +121,14 @@ def get_audio_from_item(item):
         duration_parts = item.findtext("duration").split(":")
         total_seconds = 0
         for i, num in enumerate(reversed(duration_parts)):
-            total_seconds += int(num) * (60 ** i)
+            total_seconds += int(float(num)) * (60 ** i)
         if total_seconds:
             audio_args["duration"] = total_seconds
+    else:
+        for child in item.xpath("group/content"):
+            if child.get("url") == url:
+                audio_args["duration"] = int(float(child.get("duration")))
+                break
     return Audio(url, **audio_args)