docs: document drain_video_frames and align defaults across layers

ConnectionManager and PeerConnectionManager had drain_video_frames
defaulting to False, overriding the True default in
SubscriberPeerConnection. Aligned all three layers and added a
docstring explaining the drain lifecycle.

Author: aliev

getstream/video/rtc/connection_manager.py

@@ -58,7 +58,7 @@ def __init__(
         create: bool = True,
         subscription_config: Optional[SubscriptionConfig] = None,
         max_join_retries: int = 3,
-        drain_video_frames: bool = False,
+        drain_video_frames: bool = True,
         **kwargs: Any,
     ):
         super().__init__()

getstream/video/rtc/pc.py

@@ -133,6 +133,15 @@ def __init__(
         configuration: aiortc.RTCConfiguration,
         drain_video_frames: bool = True,
     ) -> None:
+        """
+        Args:
+            drain_video_frames: When True, attaches a MediaBlackhole to each
+                incoming video track so unconsumed frames are drained
+                automatically. This prevents unbounded queue growth in
+                RTCRtpReceiver when no subscriber is consuming the track.
+                The drain is stopped once a real subscriber is added via
+                add_track_subscriber.
+        """
         logger.info(
             f"creating subscriber peer connection with configuration: {configuration}"
         )

getstream/video/rtc/peer_connection.py

@@ -28,7 +28,7 @@
 class PeerConnectionManager:
     """Manages WebRTC peer connections for publishing and subscribing."""
 
-    def __init__(self, connection_manager, drain_video_frames: bool = False):
+    def __init__(self, connection_manager, drain_video_frames: bool = True):
         self.connection_manager = connection_manager
         self._drain_video_frames = drain_video_frames
         self.publisher_pc: Optional[PublisherPeerConnection] = None