fix: Improve handling of partial and complete transcriptions in live calls

In `gemini_llm_connection.py`, accumulate partial transcription texts and emit `LlmResponse` with `partial=True` for each chunk. When the transcription is marked as `finished`, emit a final `LlmResponse` with the full accumulated text and `partial=False`.

In `runners.py`, modify `_should_append_to_history` to only add transcription events to the history when they are fully finished, preventing partial transcriptions from being added.

Co-authored-by: Hangfei Lin <hangfei@google.com>
PiperOrigin-RevId: 829029715

src/google/adk/flows/llm_flows/base_llm_flow.py

@@ -587,21 +587,19 @@ class BaseLlmFlow(ABC):
 
     # Handle transcription events ONCE per llm_response, outside the event loop
     if llm_response.input_transcription:
-      input_transcription_event = (
-          await self.transcription_manager.handle_input_transcription(
-              invocation_context, llm_response.input_transcription
-          )
+      model_response_event.input_transcription = (
+          llm_response.input_transcription
       )
-      yield input_transcription_event
+      model_response_event.partial = llm_response.partial
+      yield model_response_event
       return
 
     if llm_response.output_transcription:
-      output_transcription_event = (
-          await self.transcription_manager.handle_output_transcription(
-              invocation_context, llm_response.output_transcription
-          )
+      model_response_event.output_transcription = (
+          llm_response.output_transcription
       )
-      yield output_transcription_event
+      model_response_event.partial = llm_response.partial
+      yield model_response_event
       return
 
     # Flush audio caches based on control events using configurable settings

src/google/adk/models/gemini_llm_connection.py

@@ -35,6 +35,8 @@ class GeminiLlmConnection(BaseLlmConnection):
 
   def __init__(self, gemini_session: live.AsyncSession):
     self._gemini_session = gemini_session
+    self._input_transcription_text: str = ''
+    self._output_transcription_text: str = ''
 
   async def send_history(self, history: list[types.Content]):
     """Sends the conversation history to the gemini model.
@@ -166,15 +168,49 @@ class GeminiLlmConnection(BaseLlmConnection):
               text = ''
             yield llm_response
           if message.server_content.input_transcription:
-            llm_response = LlmResponse(
-                input_transcription=message.server_content.input_transcription,
-            )
-            yield llm_response
+            if message.server_content.input_transcription.text:
+              self._input_transcription_text += (
+                  message.server_content.input_transcription.text
+              )
+              yield LlmResponse(
+                  input_transcription=types.Transcription(
+                      text=message.server_content.input_transcription.text,
+                      finished=False,
+                  ),
+                  partial=True,
+              )
+            # finished=True and partial transcription may happen in the same
+            # message.
+            if message.server_content.input_transcription.finished:
+              yield LlmResponse(
+                  input_transcription=types.Transcription(
+                      text=self._input_transcription_text,
+                      finished=True,
+                  ),
+                  partial=False,
+              )
+              self._input_transcription_text = ''
           if message.server_content.output_transcription:
-            llm_response = LlmResponse(
-                output_transcription=message.server_content.output_transcription
-            )
-            yield llm_response
+            if message.server_content.output_transcription.text:
+              self._output_transcription_text += (
+                  message.server_content.output_transcription.text
+              )
+              yield LlmResponse(
+                  output_transcription=types.Transcription(
+                      text=message.server_content.output_transcription.text,
+                      finished=False,
+                  ),
+                  partial=True,
+              )
+            if message.server_content.output_transcription.finished:
+              yield LlmResponse(
+                  output_transcription=types.Transcription(
+                      text=self._output_transcription_text,
+                      finished=True,
+                  ),
+                  partial=False,
+              )
+              self._output_transcription_text = ''
           if message.server_content.turn_complete:
             if text:
               yield self.__build_full_text_response(text)
@@ -188,10 +224,12 @@ class GeminiLlmConnection(BaseLlmConnection):
           # in case it's an interrupted message, we merge the previous partial
           # text. Other we don't merge. because content can be none when model
           # safety threshold is triggered
-          if message.server_content.interrupted and text:
-            yield self.__build_full_text_response(text)
-            text = ''
-          yield LlmResponse(interrupted=message.server_content.interrupted)
+          if message.server_content.interrupted:
+            if text:
+              yield self.__build_full_text_response(text)
+              text = ''
+            else:
+              yield LlmResponse(interrupted=message.server_content.interrupted)
         if message.tool_call:
           if text:
             yield self.__build_full_text_response(text)

src/google/adk/runners.py

@@ -588,6 +588,10 @@ class Runner:
     # Don't append audio response from model in live mode to session.
     # The data is appended to artifacts with a reference in file_data in the
     # event.
+    # We should append non-partial events only.For example, non-finished(partial)
+    # transcription events should not be appended.
+    # Function call and function response events should be appended.
+    # Other control events should be appended.
     if is_live_call and contents._is_live_model_audio_event(event):
       return False
     return True

tests/unittests/models/test_gemini_llm_connection.py

@@ -219,3 +219,135 @@ async def test_receive_usage_metadata_and_server_content(
   )
   assert usage_response.usage_metadata == expected_usage
   assert content_response.content == mock_content
+
+
+@pytest.mark.asyncio
+async def test_receive_handles_input_transcription_fragments(
+    gemini_connection, mock_gemini_session
+):
+  """Test receive handles input transcription fragments correctly."""
+  message1 = mock.Mock()
+  message1.usage_metadata = None
+  message1.server_content = mock.Mock()
+  message1.server_content.model_turn = None
+  message1.server_content.interrupted = False
+  message1.server_content.input_transcription = types.Transcription(
+      text='Hello', finished=False
+  )
+  message1.server_content.output_transcription = None
+  message1.server_content.turn_complete = False
+  message1.tool_call = None
+  message1.session_resumption_update = None
+
+  message2 = mock.Mock()
+  message2.usage_metadata = None
+  message2.server_content = mock.Mock()
+  message2.server_content.model_turn = None
+  message2.server_content.interrupted = False
+  message2.server_content.input_transcription = types.Transcription(
+      text=' world', finished=False
+  )
+  message2.server_content.output_transcription = None
+  message2.server_content.turn_complete = False
+  message2.tool_call = None
+  message2.session_resumption_update = None
+
+  message3 = mock.Mock()
+  message3.usage_metadata = None
+  message3.server_content = mock.Mock()
+  message3.server_content.model_turn = None
+  message3.server_content.interrupted = False
+  message3.server_content.input_transcription = types.Transcription(
+      text=None, finished=True
+  )
+  message3.server_content.output_transcription = None
+  message3.server_content.turn_complete = False
+  message3.tool_call = None
+  message3.session_resumption_update = None
+
+  async def mock_receive_generator():
+    yield message1
+    yield message2
+    yield message3
+
+  receive_mock = mock.Mock(return_value=mock_receive_generator())
+  mock_gemini_session.receive = receive_mock
+
+  responses = [resp async for resp in gemini_connection.receive()]
+
+  assert len(responses) == 3
+  assert responses[0].input_transcription.text == 'Hello'
+  assert responses[0].input_transcription.finished is False
+  assert responses[0].partial is True
+  assert responses[1].input_transcription.text == ' world'
+  assert responses[1].input_transcription.finished is False
+  assert responses[1].partial is True
+  assert responses[2].input_transcription.text == 'Hello world'
+  assert responses[2].input_transcription.finished is True
+  assert responses[2].partial is False
+
+
+@pytest.mark.asyncio
+async def test_receive_handles_output_transcription_fragments(
+    gemini_connection, mock_gemini_session
+):
+  """Test receive handles output transcription fragments correctly."""
+  message1 = mock.Mock()
+  message1.usage_metadata = None
+  message1.server_content = mock.Mock()
+  message1.server_content.model_turn = None
+  message1.server_content.interrupted = False
+  message1.server_content.input_transcription = None
+  message1.server_content.output_transcription = types.Transcription(
+      text='How can', finished=False
+  )
+  message1.server_content.turn_complete = False
+  message1.tool_call = None
+  message1.session_resumption_update = None
+
+  message2 = mock.Mock()
+  message2.usage_metadata = None
+  message2.server_content = mock.Mock()
+  message2.server_content.model_turn = None
+  message2.server_content.interrupted = False
+  message2.server_content.input_transcription = None
+  message2.server_content.output_transcription = types.Transcription(
+      text=' I help?', finished=False
+  )
+  message2.server_content.turn_complete = False
+  message2.tool_call = None
+  message2.session_resumption_update = None
+
+  message3 = mock.Mock()
+  message3.usage_metadata = None
+  message3.server_content = mock.Mock()
+  message3.server_content.model_turn = None
+  message3.server_content.interrupted = False
+  message3.server_content.input_transcription = None
+  message3.server_content.output_transcription = types.Transcription(
+      text=None, finished=True
+  )
+  message3.server_content.turn_complete = False
+  message3.tool_call = None
+  message3.session_resumption_update = None
+
+  async def mock_receive_generator():
+    yield message1
+    yield message2
+    yield message3
+
+  receive_mock = mock.Mock(return_value=mock_receive_generator())
+  mock_gemini_session.receive = receive_mock
+
+  responses = [resp async for resp in gemini_connection.receive()]
+
+  assert len(responses) == 3
+  assert responses[0].output_transcription.text == 'How can'
+  assert responses[0].output_transcription.finished is False
+  assert responses[0].partial is True
+  assert responses[1].output_transcription.text == ' I help?'
+  assert responses[1].output_transcription.finished is False
+  assert responses[1].partial is True
+  assert responses[2].output_transcription.text == 'How can I help?'
+  assert responses[2].output_transcription.finished is True
+  assert responses[2].partial is False

tests/unittests/test_runners.py

@@ -775,5 +775,89 @@ class TestRunnerCacheConfig:
     assert str(runner.context_cache_config) == expected_str
 
 
+class TestRunnerShouldAppendEvent:
+  """Tests for Runner._should_append_event method."""
+
+  def setup_method(self):
+    """Set up test fixtures."""
+    self.session_service = InMemorySessionService()
+    self.artifact_service = InMemoryArtifactService()
+    self.root_agent = MockLlmAgent("root_agent")
+    self.runner = Runner(
+        app_name="test_app",
+        agent=self.root_agent,
+        session_service=self.session_service,
+        artifact_service=self.artifact_service,
+    )
+
+  def test_should_append_event_finished_input_transcription(self):
+    event = Event(
+        invocation_id="inv1",
+        author="user",
+        input_transcription=types.Transcription(text="hello", finished=True),
+    )
+    assert self.runner._should_append_event(event, is_live_call=True) is True
+
+  def test_should_append_event_unfinished_input_transcription(self):
+    event = Event(
+        invocation_id="inv1",
+        author="user",
+        input_transcription=types.Transcription(text="hello", finished=False),
+    )
+    assert self.runner._should_append_event(event, is_live_call=True) is True
+
+  def test_should_append_event_finished_output_transcription(self):
+    event = Event(
+        invocation_id="inv1",
+        author="model",
+        output_transcription=types.Transcription(text="world", finished=True),
+    )
+    assert self.runner._should_append_event(event, is_live_call=True) is True
+
+  def test_should_append_event_unfinished_output_transcription(self):
+    event = Event(
+        invocation_id="inv1",
+        author="model",
+        output_transcription=types.Transcription(text="world", finished=False),
+    )
+    assert self.runner._should_append_event(event, is_live_call=True) is True
+
+  def test_should_not_append_event_live_model_audio(self):
+    event = Event(
+        invocation_id="inv1",
+        author="model",
+        content=types.Content(
+            parts=[
+                types.Part(
+                    inline_data=types.Blob(data=b"123", mime_type="audio/pcm")
+                )
+            ]
+        ),
+    )
+    assert self.runner._should_append_event(event, is_live_call=True) is False
+
+  def test_should_append_event_non_live_model_audio(self):
+    event = Event(
+        invocation_id="inv1",
+        author="model",
+        content=types.Content(
+            parts=[
+                types.Part(
+                    inline_data=types.Blob(data=b"123", mime_type="audio/pcm")
+                )
+            ]
+        ),
+    )
+    assert self.runner._should_append_event(event, is_live_call=False) is True
+
+  def test_should_append_event_other_event(self):
+    event = Event(
+        invocation_id="inv1",
+        author="model",
+        content=types.Content(parts=[types.Part(text="text")]),
+    )
+    assert self.runner._should_append_event(event, is_live_call=True) is True
+
+
 if __name__ == "__main__":
   pytest.main([__file__])