diff --git a/src/pipecat/frames/frames.py b/src/pipecat/frames/frames.py
index 17059700a..7b2dc8aaa 100644
--- a/src/pipecat/frames/frames.py
+++ b/src/pipecat/frames/frames.py
@@ -79,7 +79,10 @@ class AudioRawFrame:
     audio: bytes
     sample_rate: int
     num_channels: int
-    num_frames: int = field(init=False)
+    num_frames: int = field(default=0, init=False)
+
+    def __post_init__(self):
+        self.num_frames = int(len(self.audio) / (self.num_channels * 2))
 
 
 @dataclass
diff --git a/src/pipecat/serializers/protobuf.py b/src/pipecat/serializers/protobuf.py
index 2adf403a5..654e87b24 100644
--- a/src/pipecat/serializers/protobuf.py
+++ b/src/pipecat/serializers/protobuf.py
@@ -34,10 +34,11 @@ class ProtobufFrameSerializer(FrameSerializer):
 
         # ignoring linter errors; we check that type(frame) is in this dict above
         proto_optional_name = self.SERIALIZABLE_TYPES[type(frame)]  # type: ignore
+        proto_attr = getattr(proto_frame, proto_optional_name)
         for field in dataclasses.fields(frame):  # type: ignore
             value = getattr(frame, field.name)
-            if value:
-                setattr(getattr(proto_frame, proto_optional_name), field.name, value)
+            if value and hasattr(proto_attr, field.name):
+                setattr(proto_attr, field.name, value)
 
         result = proto_frame.SerializeToString()
         return result