feat: Virtual loopback audio device for lossless inter-app routing#310
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alexlanderzander wants to merge 3 commits into
Open
feat: Virtual loopback audio device for lossless inter-app routing#310alexlanderzander wants to merge 3 commits into
alexlanderzander wants to merge 3 commits into
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Add a CoreAudio HAL plugin (FineTuneLoopback.driver) that creates a virtual input device called 'FineTune Loopback'. This enables DAWs like Ableton Live to record audio from any app that FineTune taps — lossless, 32-bit float, with zero additional latency. Architecture: - FineTune app taps audio → processes (vol/EQ) → writes to POSIX shared memory - HAL driver reads from shared memory → presents as virtual mic input to DAWs - Lock-free SPSC ring buffer with atomic head counters (no locks on RT thread) Components: - FineTuneLoopback/: CoreAudio HAL plugin (C++, ~1200 LOC) - FTLoopbackDriver.cpp: Full AudioServerPlugInDriverInterface implementation - SharedTypes.h: Shared memory layout (binary protocol between app & driver) - Info.plist: CFPlugIn metadata for CoreAudio discovery - FineTune/Audio/Loopback/: - LoopbackRingBuffer.swift: RT-safe shared memory writer (memcpy + atomics only) - LoopbackDeviceManager.swift: Driver lifecycle, install/uninstall, app tracking - ShmHelper.h: C wrapper for variadic shm_open (Swift interop) - AudioEngine integration: auto-enables loopback for first non-DAW app - ProcessTapController: forks processed audio to ring buffer after EQ/limiting Safety: - SPSC single-writer enforcement (one app at a time) - DAW exclusion list prevents feedback loops - Stale shared memory cleanup on restart (shm_unlink before create) - RT-safe write path: no alloc, no locks, no ObjC, no logging
- Updated FTLoopbackDriver.h to support bidirectional audio streaming, allowing applications to output to and record from the virtual device. - Changed default buffer size from 512 to 256 frames for improved performance. - Updated Info.plist to reflect version change from 1.0 to 2.0. - Modified SharedTypes.h to align default buffer frames and sample rate with driver settings, and added a new field for tracking the most recent write time. - Introduced diagnose_audio.sh script for real-time monitoring of audio issues, capturing relevant log messages for troubleshooting.
- Introduced `AudioDebugView` for real-time audio routing diagnostics, displaying app tap status, device routing, audio levels, and loopback state. - Enhanced `ProcessTapControlling` protocol with `isUnmutedCapture`, `ioStats`, and `primaryAggregateDeviceID` properties. - Implemented `BufferStats` in `LoopbackRingBuffer` for diagnostics on buffer state, including fill level, overruns, and underruns. - Added debug button to `MenuBarPopupView` to open the audio debug panel. - Integrated loopback toggle functionality in `AppRow`, `AppRowControls`, and related views, allowing users to enable/disable loopback routing. - Updated UI components to reflect loopback availability and status, ensuring a cohesive user experience.
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Wouldn't making the app use an audio driver be a bit scary for the common users? Like maybe an expert mode you can toggle which downloads the driver and allows greater customization? |
Author
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i found this interesting for my own personal use since blackhole was not working that well for me. So i am also fine with it just being a branch or fork |
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Summary
Adds a CoreAudio HAL plugin that creates a virtual input device called FineTune Loopback, enabling DAWs (Ableton Live, Logic Pro, etc.) to record audio from any app that FineTune taps — lossless, 32-bit float, zero additional latency.
Use Case
DJs and producers can now route audio from Rekordbox, Spotify, or any app directly into their DAW for recording, sampling, or live performance — without any external hardware or lossy screen-recording workarounds.
Architecture
New Files
HAL Plugin (FineTuneLoopback/)
FTLoopbackDriver.cpp— Full AudioServerPlugInDriverInterface (~1200 LOC)FTLoopbackDriver.h— Constants, supported sample rates (44.1/48/96 kHz)SharedTypes.h— Shared memory binary protocolInfo.plist— CFPlugIn metadataSwift Integration (FineTune/Audio/Loopback/)
LoopbackRingBuffer.swift— RT-safe shared memory writerLoopbackDeviceManager.swift— Driver lifecycle, admin install/uninstallShmHelper.h— C wrapper for variadic shm_openModified Files
AudioEngine.swift— Loopback lifecycle, auto-enable for non-DAW appsProcessTapController.swift— Forks processed audio to ring bufferProcessTapControlling.swift— setLoopbackBuffer protocol methodTesting
Future Improvements