pipeline: add send_initial_empty_metrics flag

CHANGELOG.md

@@ -7,6 +7,11 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 
 ## [Unrelease]
 
+### Added
+
+- Added `send_initial_empty_metrics` flag to `PipelineParams` to request for
+  initial empty metrics (zero values). True by default.
+
 ### Fixed
 
 - STT services should be using ISO 8601 time format for transcription frames.

src/pipecat/pipeline/pipeline.py

@@ -64,7 +64,7 @@ class Pipeline(BasePipeline):
         services = []
         for p in self._processors:
             if isinstance(p, BasePipeline):
-                services += p.processors_with_metrics()
+                services.extend(p.processors_with_metrics())
             elif p.can_generate_metrics():
                 services.append(p)
         return services

src/pipecat/pipeline/task.py

@@ -21,6 +21,7 @@ from loguru import logger
 class PipelineParams(BaseModel):
     allow_interruptions: bool = False
     enable_metrics: bool = False
+    send_initial_empty_metrics: bool = True
     report_only_initial_ttfb: bool = False
 
 
@@ -106,7 +107,9 @@ class PipelineTask:
             report_only_initial_ttfb=self._params.report_only_initial_ttfb
         )
         await self._source.process_frame(start_frame, FrameDirection.DOWNSTREAM)
-        await self._source.process_frame(self._initial_metrics_frame(), FrameDirection.DOWNSTREAM)
+
+        if self._params.send_initial_empty_metrics:
+            await self._source.process_frame(self._initial_metrics_frame(), FrameDirection.DOWNSTREAM)
 
         running = True
         should_cleanup = True