Add live audio transcription streaming support to Foundry Local Python SDK

[rui-ren]

Description

Adds real-time audio streaming support to the Foundry Local Python SDK, enabling live microphone-to-text transcription via ONNX Runtime GenAI's StreamingProcessor API (Nemotron ASR).

This is the Python port of C# PR #485 with full feature parity. The existing AudioClient only supports file-based transcription. This PR introduces LiveAudioTranscriptionSession that accepts continuous PCM audio chunks (e.g., from a microphone) and returns partial/final transcription results as a synchronous generator.

What's included

New files

• src/openai/live_audio_transcription_client.py — Streaming session with start(), append(), get_transcription_stream(), stop()
• src/openai/live_audio_transcription_types.py — LiveAudioTranscriptionResponse (ConversationItem-shaped), LiveAudioTranscriptionOptions, CoreErrorResponse, TranscriptionContentPart
• test/openai/test_live_audio_transcription.py — 22 unit tests for deserialization, settings, state guards, streaming pipeline
• test/openai/test_live_audio_transcription_e2e.py — E2E test with real native DLLs and nemotron model
• test/openai/conftest.py — DLL preload for E2E tests
• samples/python/live-audio-transcription/src/app.py — Live microphone transcription demo

Modified files

• src/openai/audio_client.py — Added create_live_transcription_session() factory method
• src/detail/core_interop.py — Added StreamingRequestBuffer struct, execute_command_with_binary(), start_audio_stream, push_audio_data, stop_audio_stream methods, and _load_dll_win() for robust DLL loading on Windows
• src/openai/__init__.py — Exported new live transcription types
• test/conftest.py — Pre-load ORT/GenAI DLLs before brotli import to avoid Windows DLL search conflicts

API surface

audio_client = model.get_audio_client()
session = audio_client.create_live_transcription_session()

session.settings.sample_rate = 16000
session.settings.channels = 1
session.settings.language = "en"

session.start()

# Push audio from microphone callback (thread-safe)
session.append(pcm_bytes)

# Read results as synchronous generator
for result in session.get_transcription_stream():
    print(result.content[0].text)

session.stop()

C# parity

C# API	Python API	Notes
CreateLiveTranscriptionSession()	create_live_transcription_session()	✅
StartAsync(ct)	start()	Sync (matches Python SDK convention)
AppendAsync(ReadOnlyMemory<byte>, ct)	append(bytes)	Thread-safe, copies data
GetTranscriptionStream()	get_transcription_stream()	Generator (sync equivalent of IAsyncEnumerable)
StopAsync(ct)	stop()	Drains push queue, sends native stop, surfaces final result
IAsyncDisposable	Context manager (with)	Idiomatic Python equivalent
LiveAudioTranscriptionOptions	LiveAudioTranscriptionOptions	Same fields: sample_rate, channels, bits_per_sample, language, push_queue_capacity
LiveAudioTranscriptionResponse	LiveAudioTranscriptionResponse	ConversationItem-shaped: content[0].text/transcript, is_final, start_time, end_time

Design highlights

• Output type alignment — LiveAudioTranscriptionResponse uses the OpenAI Realtime ConversationItem shape (content[0].text/transcript) for forward compatibility
• Internal push queue — Bounded queue.Queue serializes audio pushes from any thread (safe for mic callbacks) with backpressure
• Fail-fast on errors — Push loop terminates immediately on any native error (no retry logic)
• Settings freeze — Audio format settings are snapshot-copied at start() and immutable during the session
• Buffer copy — append() copies input data to avoid issues with callers reusing buffers (e.g., PyAudio)
• Routes through existing exports — start_audio_stream and stop_audio_stream route through execute_command; push_audio_data routes through execute_command_with_binary — no new native entry points required
• DLL loading fix — Uses LoadLibraryExW with LOAD_WITH_ALTERED_SEARCH_PATH on Windows to prevent conflicts with stale system-level ORT DLLs

Verified working

• ✅ 22 unit tests passing (deserialization, settings, state guards, streaming pipeline with mocked core)
• ✅ E2E test passing (SDK → Core.dll → onnxruntime-genai.dll → onnxruntime.dll with nemotron model)
• ✅ Full session lifecycle: start → push synthetic PCM → stop → verify results
• ✅ Existing tests unaffected

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Project	Deployment	Actions	Updated (UTC)
foundry-local	Ready	Preview, Comment	Apr 8, 2026 11:25pm

[Copilot]

Pull request overview

Note

Copilot was unable to run its full agentic suite in this review.

Adds end-to-end live audio (PCM chunk) streaming transcription to the Foundry Local Python SDK, including session lifecycle management, native interop support for binary payloads, and tests/samples to validate Windows DLL loading and Nemotron ASR streaming.

Changes:

• Introduces LiveAudioTranscriptionSession + supporting response/options/error types for streaming microphone-style PCM input.
• Extends CoreInterop with a StreamingRequestBuffer and execute_command_with_binary() to push raw audio to native core.
• Adds unit + E2E coverage and a sample app, including Windows DLL preload workarounds for brotli/LoadLibrary behavior.

Reviewed changes

Copilot reviewed 10 out of 10 changed files in this pull request and generated 7 comments.

Show a summary per file

File	Description
sdk/python/src/openai/live_audio_transcription_client.py	Implements the streaming session (start/append/stream/stop) and background push loop.
sdk/python/src/openai/live_audio_transcription_types.py	Adds response/options/error DTOs and JSON parsing helpers.
sdk/python/src/detail/core_interop.py	Adds binary-command execution path and Windows DLL loading hardening for ORT/GenAI.
sdk/python/src/openai/audio_client.py	Adds factory method to create the live transcription session.
sdk/python/src/openai/init.py	Exports new session and types from the openai package surface.
sdk/python/test/openai/test_live_audio_transcription.py	Unit tests for parsing/options/state guards and mocked streaming behavior.
sdk/python/test/openai/test_live_audio_transcription_e2e.py	Windows-only E2E test exercising real native DLLs and nemotron model pipeline.
sdk/python/test/openai/conftest.py	Preloads ORT/GenAI DLLs for E2E to avoid brotli-related DLL search changes.
sdk/python/test/conftest.py	Preloads ORT/GenAI DLLs early in all tests to avoid Windows DLL search conflicts.
samples/python/live-audio-transcription/src/app.py	Demonstration app using PyAudio to stream microphone PCM into the session.

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[kunal-vaishnavi]

The FL Core version is updated so this should always exist.

[kunal-vaishnavi]

Do we need to use a daemon thread? Should we make this non-daemon and require stop() + join() instead? One of the features of FL Core that we have advertised is that it does not require a daemon.

[kunal-vaishnavi]

This looks like a similar function to what is inside conftest.py. Can either this or conftest.py be removed then?

[kunal-vaishnavi]

Given there already exists a conftest.py file, can we move any modifications to that file and remove this one?

[kunal-vaishnavi]

Can we move this function into conftest.py instead so that the E2E unit tests are cleaner to look at?