introduce pipeline nodes

Make FrameProcessors async iterators and decouple them from pipeline. A new
PipelineNode now handles routing frames between processors.

CHANGELOG.md

@@ -9,6 +9,14 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 
 ### Added
 
+- Refactored pipeline architecture by introducing a new `PipelineNode`
+  abstraction.  Frame processors are now standalone async iterators, and
+  `PipelineNode` is responsible for routing frames upstream or downstream. This
+  decouples frame processors from direct linking, simplifies processor reuse,
+  and provides a clearer separation between processing logic and pipeline
+  wiring. This is an internal, transparent improvement and does not require any
+  changes to existing frame processor code.
+
 - `EndFrame` and `EndTaskFrame` have an optional `reason` field to indicate why
   the pipeline is being ended.
 
@@ -26,8 +34,9 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 
 ### Added
 
-- Added supprt for Sarvam Speech-to-Text service (`SarvamSTTService`) with streaming WebSocket
-  support for `saarika` (STT) and `saaras` (STT-translate) models.
+- Added supprt for Sarvam Speech-to-Text service (`SarvamSTTService`) with
+  streaming WebSocket support for `saarika` (STT) and `saaras` (STT-translate)
+  models.
 
 - Added a new `DeepgramHttpTTSService`, which delivers a meaningful reduction
   in latency when compared to the `DeepgramTTSService`.

src/pipecat/pipeline/pipeline.py

@@ -15,6 +15,7 @@ from typing import Callable, Coroutine, List, Optional
 
 from pipecat.frames.frames import Frame
 from pipecat.pipeline.base_pipeline import BasePipeline
+from pipecat.pipeline.pipeline_node import PipelineNode
 from pipecat.processors.frame_processor import FrameDirection, FrameProcessor, FrameProcessorSetup
 
 
@@ -117,8 +118,7 @@ class Pipeline(BasePipeline):
         self._source = source or PipelineSource(self.push_frame, name=f"{self}::Source")
         self._sink = sink or PipelineSink(self.push_frame, name=f"{self}::Sink")
         self._processors: List[FrameProcessor] = [self._source] + processors + [self._sink]
-
-        self._link_processors()
+        self._nodes = self._link_processors()
 
     #
     # Frame processor
@@ -196,17 +196,22 @@ class Pipeline(BasePipeline):
 
     async def _setup_processors(self, setup: FrameProcessorSetup):
         """Set up all processors in the pipeline."""
-        for p in self._processors:
-            await p.setup(setup)
+        for n in self._nodes:
+            await n.setup(setup)
 
     async def _cleanup_processors(self):
         """Clean up all processors in the pipeline."""
-        for p in self._processors:
-            await p.cleanup()
+        for n in self._nodes:
+            await n.cleanup()
 
-    def _link_processors(self):
-        """Link all processors in sequence and set their parent."""
-        prev = self._processors[0]
+    def _link_processors(self) -> List[PipelineNode]:
+        """Link all processors in sequence."""
+        nodes = []
+        prev_node = PipelineNode(self._processors[0])
+        nodes.append(prev_node)
         for curr in self._processors[1:]:
-            prev.link(curr)
-            prev = curr
+            curr_node = PipelineNode(curr)
+            nodes.append(curr_node)
+            prev_node.link(curr_node)
+            prev_node = curr_node
+        return nodes

src/pipecat/pipeline/pipeline_node.py

@@ -0,0 +1,140 @@
+#
+# Copyright (c) 2024–2025, Daily
+#
+# SPDX-License-Identifier: BSD 2-Clause License
+#
+
+"""This module defines pipeline nodes.
+
+A pipeline node (`PipelineNode`) wraps a frame processor (`FrameProcessor`) and
+can link to previous and next nodes in the pipeline. Pipeline nodes allow
+linking frame processors together with the benefit that stateless frame
+processors can be re-used in different pipelines, since what is linked is the
+actual pipeline node, not the frame processor itself.
+
+"""
+
+import asyncio
+from typing import Optional
+
+from loguru import logger
+
+from pipecat.observers.base_observer import FramePushed
+from pipecat.processors.frame_processor import FrameDirection, FrameProcessor, FrameProcessorSetup
+from pipecat.utils.base_object import BaseObject
+
+
+class PipelineNode(BaseObject):
+    """A node in a pipeline that hosts a frame processor.
+
+    A `PipelineNode` wraps a single `FrameProcessor` and is responsible for
+    connecting it to previous and next nodes in a pipeline. It pushes frames
+    emitted by its processor to the appropriate neighbor based on frame
+    direction (UPSTREAM or DOWNSTREAM).
+    """
+
+    def __init__(self, processor: FrameProcessor):
+        """Initialize the pipeline node with a given FrameProcessor.
+
+        Args:
+            processor: The FrameProcessor instance that this node will host.
+        """
+        super().__init__()
+        self._processor = processor
+
+        self._prev: Optional["PipelineNode"] = None
+        self._next: Optional["PipelineNode"] = None
+
+        self.__push_task: Optional[asyncio.Task] = None
+
+    @property
+    def processor(self) -> FrameProcessor:
+        """Returns the frame processor of this pipeline node."""
+        return self._processor
+
+    @property
+    def next(self) -> Optional["PipelineNode"]:
+        """Get the next pipeline node.
+
+        Returns:
+            The next node, or None if there's no next node.
+        """
+        return self._next
+
+    @property
+    def previous(self) -> Optional["PipelineNode"]:
+        """Get the previous pipeline node.
+
+        Returns:
+            The previous node, or None if there's no previous node.
+        """
+        return self._prev
+
+    async def setup(self, setup: FrameProcessorSetup):
+        """Set up this pipeline node.
+
+        This sets up the wrapped frame processor with required components.
+
+        Args:
+            setup: Configuration object containing setup parameters.
+        """
+        await self.processor.setup(setup)
+        self._clock = setup.clock
+        self._task_manager = setup.task_manager
+        self._observer = setup.observer
+
+        self.__create_push_task()
+
+    async def cleanup(self):
+        """Clean up this pipeline node."""
+        await super().cleanup()
+        await self.processor.cleanup()
+        if self.__push_task:
+            await self.__push_task
+            self.__push_task = None
+
+    def link(self, node: "PipelineNode"):
+        """Link this node to the next node in the pipeline.
+
+        Args:
+            node: The node to link to.
+        """
+        self._next = node
+        node._prev = self
+        logger.debug(f"Linking {self.processor} -> {node.processor}")
+
+    def __create_push_task(self):
+        """Create the frame push task."""
+        if not self.__push_task:
+            self.__push_task = self._task_manager.create_task(
+                self.__push_task_handler(), f"{self.processor}::_push_task"
+            )
+
+    async def __push_task_handler(self):
+        """Push task handler.
+
+        Receive frames from the wrapped frame processor and push them to the
+        next or previous node depending on the direction.
+        """
+        async for frame, direction in self.processor:
+            destination = None
+            if direction == FrameDirection.DOWNSTREAM and self.next:
+                logger.trace(f"Pushing {frame} from {self.processor} to {self.next.processor}")
+                destination = self.next.processor
+            elif direction == FrameDirection.UPSTREAM and self.previous:
+                logger.trace(f"Pushing {frame} upstream from {self} to {self._prev}")
+                destination = self.previous.processor
+
+            if destination:
+                await destination.queue_frame(frame, direction)
+
+            if self._observer and destination:
+                timestamp = self._clock.get_time() if self._clock else 0
+                data = FramePushed(
+                    source=self.processor,
+                    destination=destination,
+                    frame=frame,
+                    direction=direction,
+                    timestamp=timestamp,
+                )
+                await self._observer.on_push_frame(data)

src/pipecat/processors/frame_processor.py

@@ -132,14 +132,17 @@ INPUT_TASK_CANCEL_TIMEOUT_SECS = 3
 
 
 class FrameProcessor(BaseObject):
-    """Base class for all frame processors in the pipeline.
+    """Base class for all frame processors in Pipecat.
 
-    Frame processors are the building blocks of Pipecat pipelines, they can be
-    linked to form complex processing pipelines. They receive frames, process
-    them, and pass them to the next or previous processor in the chain.  Each
-    frame processor guarantees frame ordering and processes frames in its own
-    task. System frames are also processed in a separate task which guarantees
-    frame priority.
+    A FrameProcessor is an independent, asynchronous component that consumes
+    input frames and produces zero or more output frames. Frames are delivered
+    to the processor via the `queue_frame(frame, direction)` method. The
+    processor internally manages queues and background tasks to handle incoming
+    frames and generate output frames.
+
+    Output frames are made available through the processor's asynchronous
+    iterator interface, allowing consumers to iterate over processed frames
+    using `async for frame in processor`. Frame ordering is guaranteed.
 
     Event handlers available:
 
@@ -147,6 +150,7 @@ class FrameProcessor(BaseObject):
     - on_after_process_frame: Called after a frame is processed
     - on_before_push_frame: Called before a frame is pushed
     - on_after_push_frame: Called after a frame is pushed
+
     """
 
     def __init__(
@@ -166,8 +170,6 @@ class FrameProcessor(BaseObject):
             **kwargs: Additional arguments passed to parent class.
         """
         super().__init__(name=name, **kwargs)
-        self._prev: Optional["FrameProcessor"] = None
-        self._next: Optional["FrameProcessor"] = None
 
         # Enable direct mode to skip queues and process frames right away.
         self._enable_direct_mode = enable_direct_mode
@@ -234,6 +236,9 @@ class FrameProcessor(BaseObject):
         self._wait_for_interruption = False
         self._wait_interruption_event = asyncio.Event()
 
+        # Push queue
+        self.__push_queue = asyncio.Queue()
+
         # Frame processor events.
         self._register_event_handler("on_before_process_frame", sync=True)
         self._register_event_handler("on_after_process_frame", sync=True)
@@ -284,24 +289,6 @@ class FrameProcessor(BaseObject):
         """
         return []
 
-    @property
-    def next(self) -> Optional["FrameProcessor"]:
-        """Get the next processor.
-
-        Returns:
-            The next processor, or None if there's no next processor.
-        """
-        return self._next
-
-    @property
-    def previous(self) -> Optional["FrameProcessor"]:
-        """Get the previous processor.
-
-        Returns:
-            The previous processor, or None if there's no previous processor.
-        """
-        return self._prev
-
     @property
     def interruptions_allowed(self):
         """Check if interruptions are allowed for this processor.
@@ -518,16 +505,7 @@ class FrameProcessor(BaseObject):
         await self.__cancel_process_task()
         if self._metrics is not None:
             await self._metrics.cleanup()
-
-    def link(self, processor: "FrameProcessor"):
-        """Link this processor to the next processor in the pipeline.
-
-        Args:
-            processor: The processor to link to.
-        """
-        self._next = processor
-        processor._prev = self
-        logger.debug(f"Linking {self} -> {self._next}")
+        await self.__push_queue.put(None)
 
     def get_clock(self) -> BaseClock:
         """Get the clock used by this processor.
@@ -761,36 +739,7 @@ class FrameProcessor(BaseObject):
             frame: The frame to push.
             direction: The direction to push the frame.
         """
-        try:
-            timestamp = self._clock.get_time() if self._clock else 0
-            if direction == FrameDirection.DOWNSTREAM and self._next:
-                logger.trace(f"Pushing {frame} from {self} to {self._next}")
-
-                if self._observer:
-                    data = FramePushed(
-                        source=self,
-                        destination=self._next,
-                        frame=frame,
-                        direction=direction,
-                        timestamp=timestamp,
-                    )
-                    await self._observer.on_push_frame(data)
-                await self._next.queue_frame(frame, direction)
-            elif direction == FrameDirection.UPSTREAM and self._prev:
-                logger.trace(f"Pushing {frame} upstream from {self} to {self._prev}")
-                if self._observer:
-                    data = FramePushed(
-                        source=self,
-                        destination=self._prev,
-                        frame=frame,
-                        direction=direction,
-                        timestamp=timestamp,
-                    )
-                    await self._observer.on_push_frame(data)
-                await self._prev.queue_frame(frame, direction)
-        except Exception as e:
-            logger.exception(f"Uncaught exception in {self}: {e}")
-            await self.push_error(ErrorFrame(str(e)))
+        await self.__push_queue.put((frame, direction))
 
     def _check_started(self, frame: Frame):
         """Check if the processor has been started.
@@ -912,3 +861,18 @@ class FrameProcessor(BaseObject):
             await self.__process_frame(frame, direction, callback)
 
             self.__process_queue.task_done()
+
+    def __aiter__(self):
+        """A frame processor is an asynchronous iterator itself."""
+        return self
+
+    async def __anext__(self):
+        """Retrieve the next frame to push from this processor.
+
+        Returns:
+            The next (frame, direction) item to push form this processor.
+        """
+        data = await self.__push_queue.get()
+        if data is None:
+            raise StopAsyncIteration
+        return data