Voice Pipeline Lifecycle

Use this reference for changes to VoicePipeline, AudioInput, StreamedAudioInput, STT sessions, TTS task ordering, voice lifecycle events, PCM framing, result streaming, or voice tracing. Realtime agents use a different live-session architecture; read Realtime session lifecycle for that path.

Pipeline Ownership

VoicePipeline owns an STT-to-workflow-to-TTS producer task and returns a StreamedAudioResult that drives its observable completion.

• Static AudioInput produces one transcription and one workflow turn. StreamedAudioInput creates a long-lived transcription session and runs one workflow turn for each emitted transcript until the input or session ends.
• The multi-turn pipeline owns the transcription session and closes it in finally before marking output complete. Partial setup and workflow failure must not strand the STT connection or producer task.
• workflow.on_start() applies only to the streamed multi-turn path. Its failure is logged and skipped so the transcription session can still start; normal per-turn workflow failures are terminal and surface through the result stream.
• The SDK does not provide application-level interruption handling for StreamedAudioInput. Lifecycle events expose turn boundaries, but microphone muting, playback interruption, and barge-in policy remain application-owned.

Text, Audio, and Event Ordering

• A workflow can yield multiple text fragments. The text splitter returns ready-to-synthesize text plus a remainder; synthesize non-empty ready text even when it is shorter than a default sentence threshold, and retain the remainder for the turn's final flush.
• TTS segment tasks may run concurrently, but _ordered_tasks and the dispatcher must emit their audio and lifecycle events in workflow text order rather than completion order.
• turn_started precedes audio for that turn. turn_ended is emitted only after the turn's final text remainder has been synthesized and its audio dispatched. session_ended follows all ordered segment queues and all turns.
• A VoiceStreamEventError terminates result streaming and the stored exception is raised after task cleanup. session_ended is a lifecycle marker, not proof of success; consumers must still observe the terminal exception from stream().
• Consuming StreamedAudioResult.stream() is the public completion and error boundary. On normal session_ended, let the producer finish before cleanup so session close and trace end are not cancelled by result teardown.

PCM and Caller Data

• PCM16 samples span two bytes. Preserve a trailing half-sample across TTS chunks, combine it with the next chunk, and pad only the final unmatched byte at end of segment.
• Apply buffer_size to TTS source chunks without changing sample order. Convert to float32 only after PCM16 framing is complete, then apply caller-provided transform_data to each emitted array.
• AudioInput.to_base64() and audio-file conversion must not mutate the caller's NumPy buffer when converting float input to PCM16.
• Empty input and empty text-splitter output are valid boundaries. They must not cause NumPy reduction errors, phantom TTS calls, or missing turn/session lifecycle events.

Trace Lifetime and Data

• The pipeline trace stays active for the full asynchronous producer lifecycle, not only until VoicePipeline.run() returns its result object.
• Each output turn owns a speech-group span and each synthesized segment owns a child speech span. Finish the turn span after ordered audio dispatch and finish the pipeline trace after STT session close and output completion.
• Text and audio sensitivity are independent controls. trace_include_sensitive_data governs transcript and TTS text, while trace_include_sensitive_audio_data governs encoded audio payloads.
• Error paths must finish active speech spans and the enclosing trace without replacing the original pipeline exception.

Review Checklist

1. Test static and streamed input, including STT setup failure, workflow failure, TTS failure, and transcription-session close.
2. Verify fragment concurrency never changes audio, turn, or session event order.
3. Test short splitter output, empty output, odd-byte chunks, cross-chunk sample boundaries, int16, and float32 conversion.
4. Consume the public result stream and verify terminal errors, task cleanup, session close, and trace-end order.
5. Confirm sensitive text and audio are independently omitted from trace payloads.

Sources

• docs/voice/pipeline.md
• docs/voice/tracing.md
• src/agents/voice/pipeline.py
• src/agents/voice/result.py
• src/agents/voice/input.py
• src/agents/voice/model.py
• src/agents/voice/models/openai_stt.py
• tests/voice/test_pipeline.py
• tests/voice/test_input.py
• tests/voice/test_openai_stt.py
• tests/voice/test_openai_tts.py