native macos backend, reduce latency

native/binding.gyp

@@ -19,13 +19,25 @@
       "defines": ["NAPI_DISABLE_CPP_EXCEPTIONS"],
       "conditions": [
         ["OS=='mac'", {
+          "sources": [
+            "src/macos_capture.mm"
+          ],
           "xcode_settings": {
             "GCC_ENABLE_CPP_EXCEPTIONS": "YES",
             "CLANG_CXX_LIBRARY": "libc++",
-            "MACOSX_DEPLOYMENT_TARGET": "10.15"
+            "CLANG_ENABLE_OBJC_ARC": "YES",
+            "MACOSX_DEPLOYMENT_TARGET": "10.15",
+            "OTHER_LDFLAGS": [
+              "-framework Foundation",
+              "-framework CoreAudio",
+              "-framework AudioToolbox"
+            ]
           }
         }],
         ["OS=='win'", {
+          "sources": [
+            "src/macos_capture_stub.cpp"
+          ],
           "msvs_settings": {
             "VCCLCompilerTool": {
               "ExceptionHandling": 1,
@@ -34,6 +46,9 @@
           }
         }],
         ["OS=='linux'", {
+          "sources": [
+            "src/macos_capture_stub.cpp"
+          ],
           "cflags_cc": ["-std=c++17", "-O3", "-ffast-math", "-fPIC"]
         }]
       ]

native/src/macos_capture.h

@@ -0,0 +1,5 @@
+#pragma once
+
+#include <napi.h>
+
+void RegisterMacOSCapture(Napi::Env env, Napi::Object exports);

native/src/macos_capture.mm

@@ -0,0 +1,839 @@
+#include "macos_capture.h"
+
+#if defined(__APPLE__)
+
+#import <Foundation/Foundation.h>
+#import <CoreAudio/CoreAudio.h>
+#import <CoreAudio/AudioHardwareTapping.h>
+#import <CoreAudio/CATapDescription.h>
+
+#include <algorithm>
+#include <chrono>
+#include <cstdint>
+#include <cstring>
+#include <deque>
+#include <limits>
+#include <mutex>
+#include <string>
+#include <vector>
+
+namespace {
+
+constexpr size_t kMaxQueuedChunks = 256;
+constexpr size_t kDefaultDrainChunkLimit = 64;
+constexpr AudioObjectID kUnknownObject = kAudioObjectUnknown;
+
+struct OutputDeviceInfo {
+    std::string uid;
+    std::string label;
+    double sampleRate;
+    UInt32 channelCount;
+    bool isDefault;
+};
+
+struct CapturedChunk {
+    std::vector<float> left;
+    std::vector<float> right;
+    UInt32 channelCount = 2;
+    double capturedAtMilliseconds = 0.0;
+    uint64_t sequence = 0;
+};
+
+double monotonicMilliseconds() {
+    const auto now = std::chrono::steady_clock::now().time_since_epoch();
+    return std::chrono::duration<double, std::milli>(now).count();
+}
+
+std::string cfStringToStdString(CFStringRef value) {
+    if (value == nullptr) {
+        return {};
+    }
+
+    const CFIndex length = CFStringGetLength(value);
+    const CFIndex maxBytes =
+        CFStringGetMaximumSizeForEncoding(length, kCFStringEncodingUTF8) + 1;
+    std::vector<char> buffer(static_cast<size_t>(std::max<CFIndex>(1, maxBytes)), '\0');
+
+    if (!CFStringGetCString(value, buffer.data(), maxBytes, kCFStringEncodingUTF8)) {
+        return {};
+    }
+
+    return std::string(buffer.data());
+}
+
+NSString* toNSString(const std::string& value) {
+    return [[NSString alloc] initWithUTF8String:value.c_str()];
+}
+
+template <typename T>
+bool getPropertyData(AudioObjectID objectId,
+                     AudioObjectPropertySelector selector,
+                     AudioObjectPropertyScope scope,
+                     AudioObjectPropertyElement element,
+                     T* outValue) {
+    if (outValue == nullptr) {
+        return false;
+    }
+
+    AudioObjectPropertyAddress address{
+        selector,
+        scope,
+        element,
+    };
+
+    UInt32 size = sizeof(T);
+    return AudioObjectGetPropertyData(objectId, &address, 0, nullptr, &size, outValue) == noErr;
+}
+
+bool getDeviceStringProperty(AudioDeviceID deviceId,
+                             AudioObjectPropertySelector selector,
+                             std::string* outValue) {
+    if (outValue == nullptr) {
+        return false;
+    }
+
+    AudioObjectPropertyAddress address{
+        selector,
+        kAudioObjectPropertyScopeGlobal,
+        kAudioObjectPropertyElementMain,
+    };
+
+    CFStringRef stringValue = nullptr;
+    UInt32 size = sizeof(stringValue);
+    const OSStatus status =
+        AudioObjectGetPropertyData(deviceId, &address, 0, nullptr, &size, &stringValue);
+    if (status != noErr || stringValue == nullptr) {
+        return false;
+    }
+
+    *outValue = cfStringToStdString(stringValue);
+    CFRelease(stringValue);
+    return !outValue->empty();
+}
+
+AudioDeviceID getDefaultOutputDeviceId() {
+    AudioDeviceID deviceId = kUnknownObject;
+    if (!getPropertyData(kAudioObjectSystemObject,
+                         kAudioHardwarePropertyDefaultOutputDevice,
+                         kAudioObjectPropertyScopeGlobal,
+                         kAudioObjectPropertyElementMain,
+                         &deviceId)) {
+        return kUnknownObject;
+    }
+    return deviceId;
+}
+
+bool getDeviceNominalSampleRate(AudioDeviceID deviceId, double* outSampleRate) {
+    if (outSampleRate == nullptr) {
+        return false;
+    }
+
+    Float64 sampleRate = 0.0;
+    if (!getPropertyData(deviceId,
+                         kAudioDevicePropertyNominalSampleRate,
+                         kAudioObjectPropertyScopeGlobal,
+                         kAudioObjectPropertyElementMain,
+                         &sampleRate)) {
+        return false;
+    }
+
+    if (sampleRate <= 0.0) {
+        return false;
+    }
+
+    *outSampleRate = static_cast<double>(sampleRate);
+    return true;
+}
+
+UInt32 getOutputChannelCount(AudioDeviceID deviceId) {
+    AudioObjectPropertyAddress address{
+        kAudioDevicePropertyStreamConfiguration,
+        kAudioDevicePropertyScopeOutput,
+        kAudioObjectPropertyElementMain,
+    };
+
+    UInt32 size = 0;
+    if (AudioObjectGetPropertyDataSize(deviceId, &address, 0, nullptr, &size) != noErr ||
+        size == 0) {
+        return 0;
+    }
+
+    std::vector<uint8_t> storage(size);
+    auto* bufferList = reinterpret_cast<AudioBufferList*>(storage.data());
+    if (AudioObjectGetPropertyData(deviceId, &address, 0, nullptr, &size, bufferList) !=
+        noErr) {
+        return 0;
+    }
+
+    UInt32 channelCount = 0;
+    for (UInt32 index = 0; index < bufferList->mNumberBuffers; ++index) {
+        channelCount += bufferList->mBuffers[index].mNumberChannels;
+    }
+
+    return channelCount;
+}
+
+std::vector<OutputDeviceInfo> enumerateOutputDevices() {
+    AudioObjectPropertyAddress address{
+        kAudioHardwarePropertyDevices,
+        kAudioObjectPropertyScopeGlobal,
+        kAudioObjectPropertyElementMain,
+    };
+
+    UInt32 size = 0;
+    if (AudioObjectGetPropertyDataSize(kAudioObjectSystemObject, &address, 0, nullptr, &size) !=
+            noErr ||
+        size == 0) {
+        return {};
+    }
+
+    const UInt32 deviceCount = size / sizeof(AudioDeviceID);
+    std::vector<AudioDeviceID> deviceIds(deviceCount, kUnknownObject);
+    if (AudioObjectGetPropertyData(
+            kAudioObjectSystemObject, &address, 0, nullptr, &size, deviceIds.data()) != noErr) {
+        return {};
+    }
+
+    const AudioDeviceID defaultDeviceId = getDefaultOutputDeviceId();
+    std::vector<OutputDeviceInfo> devices;
+    devices.reserve(deviceCount);
+
+    for (AudioDeviceID deviceId : deviceIds) {
+        const UInt32 channelCount = getOutputChannelCount(deviceId);
+        if (channelCount == 0) {
+            continue;
+        }
+
+        std::string uid;
+        if (!getDeviceStringProperty(deviceId, kAudioDevicePropertyDeviceUID, &uid)) {
+            continue;
+        }
+
+        std::string label;
+        if (!getDeviceStringProperty(deviceId, kAudioObjectPropertyName, &label)) {
+            label = uid;
+        }
+
+        double sampleRate = 0.0;
+        if (!getDeviceNominalSampleRate(deviceId, &sampleRate)) {
+            sampleRate = 48000.0;
+        }
+
+        devices.push_back(OutputDeviceInfo{
+            uid,
+            label,
+            sampleRate,
+            channelCount,
+            deviceId == defaultDeviceId,
+        });
+    }
+
+    return devices;
+}
+
+bool getTapFormat(AudioObjectID tapId, AudioStreamBasicDescription* outFormat) {
+    if (outFormat == nullptr) {
+        return false;
+    }
+
+    AudioObjectPropertyAddress address{
+        kAudioTapPropertyFormat,
+        kAudioObjectPropertyScopeGlobal,
+        kAudioObjectPropertyElementMain,
+    };
+
+    UInt32 size = sizeof(AudioStreamBasicDescription);
+    return AudioObjectGetPropertyData(tapId, &address, 0, nullptr, &size, outFormat) == noErr;
+}
+
+float decodeSignedIntegerSample(const uint8_t* data, UInt32 bytesPerSample, bool isBigEndian) {
+    if (data == nullptr || bytesPerSample == 0 || bytesPerSample > 4) {
+        return 0.0f;
+    }
+
+    int32_t rawValue = 0;
+    if (isBigEndian) {
+        for (UInt32 byteIndex = 0; byteIndex < bytesPerSample; ++byteIndex) {
+            rawValue = (rawValue << 8) | data[byteIndex];
+        }
+    } else {
+        for (UInt32 byteIndex = 0; byteIndex < bytesPerSample; ++byteIndex) {
+            rawValue |= static_cast<int32_t>(data[byteIndex]) << (byteIndex * 8);
+        }
+    }
+
+    const UInt32 totalBits = bytesPerSample * 8;
+    const int32_t signMask = 1 << (totalBits - 1);
+    if ((rawValue & signMask) != 0) {
+        rawValue |= ~((1 << totalBits) - 1);
+    }
+
+    const double maxMagnitude = static_cast<double>((1u << (totalBits - 1)) - 1u);
+    if (maxMagnitude <= 0.0) {
+        return 0.0f;
+    }
+
+    return static_cast<float>(static_cast<double>(rawValue) / maxMagnitude);
+}
+
+float readSampleFromFormat(const uint8_t* data,
+                           const AudioStreamBasicDescription& format,
+                           UInt32 sampleIndex) {
+    if (data == nullptr) {
+        return 0.0f;
+    }
+
+    const UInt32 bytesPerChannel = format.mBitsPerChannel / 8;
+    if (bytesPerChannel == 0) {
+        return 0.0f;
+    }
+
+    const uint8_t* samplePtr = data + static_cast<size_t>(sampleIndex) * bytesPerChannel;
+    const bool isFloat = (format.mFormatFlags & kAudioFormatFlagIsFloat) != 0;
+    const bool isBigEndian = (format.mFormatFlags & kAudioFormatFlagIsBigEndian) != 0;
+
+    if (isFloat && format.mBitsPerChannel == 32) {
+        Float32 value = 0.0f;
+        std::memcpy(&value, samplePtr, sizeof(Float32));
+        return value;
+    }
+
+    if (isFloat && format.mBitsPerChannel == 64) {
+        Float64 value = 0.0;
+        std::memcpy(&value, samplePtr, sizeof(Float64));
+        return static_cast<float>(value);
+    }
+
+    if ((format.mFormatFlags & kAudioFormatFlagIsSignedInteger) != 0) {
+        return decodeSignedIntegerSample(samplePtr, bytesPerChannel, isBigEndian);
+    }
+
+    return 0.0f;
+}
+
+bool isFormatInterleaved(const AudioStreamBasicDescription& format) {
+    return (format.mFormatFlags & kAudioFormatFlagIsNonInterleaved) == 0;
+}
+
+std::string formatStatusMessage(const char* operation, OSStatus status) {
+    return std::string(operation) + " failed (" + std::to_string(static_cast<int>(status)) + ")";
+}
+
+class MacOSNativeCaptureEngine {
+public:
+    Napi::Object GetSupport(Napi::Env env) {
+        Napi::Object support = Napi::Object::New(env);
+
+        if (@available(macOS 14.2, *)) {
+            support.Set("available", Napi::Boolean::New(env, true));
+            support.Set("reason", env.Null());
+            return support;
+        }
+
+        support.Set("available", Napi::Boolean::New(env, false));
+        support.Set(
+            "reason",
+            Napi::String::New(env, "Native output-device capture requires macOS 14.2 or newer."));
+        return support;
+    }
+
+    Napi::Array ListOutputDevices(Napi::Env env) {
+        Napi::Array result = Napi::Array::New(env);
+        if (!isSupported()) {
+            return result;
+        }
+
+        const auto devices = enumerateOutputDevices();
+        for (size_t index = 0; index < devices.size(); ++index) {
+            const auto& device = devices[index];
+            Napi::Object entry = Napi::Object::New(env);
+            entry.Set("id", Napi::String::New(env, device.uid));
+            entry.Set("label", Napi::String::New(env, device.label));
+            entry.Set("kind", Napi::String::New(env, "system"));
+            entry.Set("isDefault", Napi::Boolean::New(env, device.isDefault));
+            entry.Set("sampleRate", Napi::Number::New(env, device.sampleRate));
+            entry.Set(
+                "channelCount",
+                Napi::Number::New(env, static_cast<double>(device.channelCount)));
+            result.Set(static_cast<uint32_t>(index), entry);
+        }
+
+        return result;
+    }
+
+    Napi::Object Start(Napi::Env env, const std::string& requestedDeviceUid) {
+        Napi::Object result = Napi::Object::New(env);
+
+        const Napi::Object support = GetSupport(env);
+        if (!support.Get("available").As<Napi::Boolean>().Value()) {
+            Napi::Error::New(
+                env, support.Get("reason").As<Napi::String>().Utf8Value())
+                .ThrowAsJavaScriptException();
+            return result;
+        }
+
+        std::string errorMessage;
+        if (!startInternal(requestedDeviceUid, &errorMessage)) {
+            Napi::Error::New(env, errorMessage).ThrowAsJavaScriptException();
+            return result;
+        }
+
+        std::lock_guard<std::mutex> lock(stateMutex_);
+        result.Set("sampleRate", Napi::Number::New(env, sampleRate_));
+        result.Set("channelCount", Napi::Number::New(env, static_cast<double>(channelCount_)));
+        result.Set("deviceId", Napi::String::New(env, activeDeviceUid_));
+        result.Set("deviceLabel", Napi::String::New(env, activeDeviceLabel_));
+        return result;
+    }
+
+    void Stop() {
+        std::lock_guard<std::mutex> lock(stateMutex_);
+        stopLocked();
+    }
+
+    Napi::Object Drain(Napi::Env env, size_t maxChunks) {
+        const size_t drainLimit =
+            maxChunks == 0 ? kDefaultDrainChunkLimit : std::min(maxChunks, kMaxQueuedChunks);
+
+        std::deque<CapturedChunk> drained;
+        uint64_t overwriteCount = 0;
+
+        {
+            std::lock_guard<std::mutex> queueLock(chunkMutex_);
+            overwriteCount = overwriteCount_;
+            const size_t count = std::min(drainLimit, chunkQueue_.size());
+            for (size_t index = 0; index < count; ++index) {
+                drained.push_back(std::move(chunkQueue_.front()));
+                chunkQueue_.pop_front();
+            }
+        }
+
+        Napi::Array chunks = Napi::Array::New(env, drained.size());
+        for (size_t index = 0; index < drained.size(); ++index) {
+            CapturedChunk& chunk = drained[index];
+            Napi::Object entry = Napi::Object::New(env);
+            Napi::Float32Array left =
+                Napi::Float32Array::New(env, chunk.left.size());
+            Napi::Float32Array right =
+                Napi::Float32Array::New(env, chunk.right.size());
+            if (!chunk.left.empty()) {
+                std::memcpy(
+                    left.Data(), chunk.left.data(), chunk.left.size() * sizeof(float));
+            }
+            if (!chunk.right.empty()) {
+                std::memcpy(
+                    right.Data(), chunk.right.data(), chunk.right.size() * sizeof(float));
+            }
+            entry.Set("left", left);
+            entry.Set("right", right);
+            entry.Set(
+                "channelCount",
+                Napi::Number::New(env, static_cast<double>(chunk.channelCount)));
+            entry.Set(
+                "capturedAtMilliseconds",
+                Napi::Number::New(env, chunk.capturedAtMilliseconds));
+            entry.Set(
+                "sequence",
+                Napi::Number::New(env, static_cast<double>(chunk.sequence)));
+            chunks.Set(static_cast<uint32_t>(index), entry);
+        }
+
+        Napi::Object result = Napi::Object::New(env);
+        result.Set("chunks", chunks);
+        result.Set(
+            "overwriteCount",
+            Napi::Number::New(env, static_cast<double>(overwriteCount)));
+        result.Set(
+            "queueDepth",
+            Napi::Number::New(env, static_cast<double>(chunkQueue_.size())));
+        return result;
+    }
+
+    double NowMilliseconds() const {
+        return monotonicMilliseconds();
+    }
+
+private:
+    static OSStatus StaticIOProc(AudioObjectID inDevice,
+                                 const AudioTimeStamp* inNow,
+                                 const AudioBufferList* inInputData,
+                                 const AudioTimeStamp* inInputTime,
+                                 AudioBufferList* outOutputData,
+                                 const AudioTimeStamp* inOutputTime,
+                                 void* inClientData) {
+        auto* self = static_cast<MacOSNativeCaptureEngine*>(inClientData);
+        if (self == nullptr) {
+            return noErr;
+        }
+        return self->handleIO(
+            inDevice, inNow, inInputData, inInputTime, outOutputData, inOutputTime);
+    }
+
+    OSStatus handleIO(AudioObjectID,
+                      const AudioTimeStamp*,
+                      const AudioBufferList* inputData,
+                      const AudioTimeStamp*,
+                      AudioBufferList*,
+                      const AudioTimeStamp*) {
+        AudioStreamBasicDescription format{};
+        UInt32 channelCount = 0;
+
+        {
+            std::lock_guard<std::mutex> stateLock(stateMutex_);
+            if (!active_ || inputData == nullptr) {
+                return noErr;
+            }
+            format = tapFormat_;
+            channelCount = channelCount_;
+        }
+
+        if (inputData->mNumberBuffers == 0 || format.mBytesPerFrame == 0) {
+            return noErr;
+        }
+
+        const bool interleaved = isFormatInterleaved(format);
+        const AudioBuffer& firstBuffer = inputData->mBuffers[0];
+        const UInt32 frames =
+            format.mBytesPerFrame == 0 ? 0 : firstBuffer.mDataByteSize / format.mBytesPerFrame;
+        if (frames == 0) {
+            return noErr;
+        }
+
+        CapturedChunk chunk;
+        chunk.channelCount = channelCount;
+        chunk.capturedAtMilliseconds = monotonicMilliseconds();
+
+        {
+            std::lock_guard<std::mutex> stateLock(stateMutex_);
+            chunk.sequence = ++sequence_;
+        }
+
+        chunk.left.resize(frames);
+        chunk.right.resize(frames);
+
+        if (interleaved) {
+            const uint8_t* rawData = static_cast<const uint8_t*>(firstBuffer.mData);
+            for (UInt32 frameIndex = 0; frameIndex < frames; ++frameIndex) {
+                const UInt32 sampleBaseIndex = frameIndex * std::max<UInt32>(1, channelCount);
+                const float leftSample =
+                    readSampleFromFormat(rawData, format, sampleBaseIndex);
+                const float rightSample = channelCount > 1
+                    ? readSampleFromFormat(rawData, format, sampleBaseIndex + 1)
+                    : leftSample;
+                chunk.left[frameIndex] = leftSample;
+                chunk.right[frameIndex] = rightSample;
+            }
+        } else {
+            const uint8_t* leftData = static_cast<const uint8_t*>(inputData->mBuffers[0].mData);
+            const uint8_t* rightData = static_cast<const uint8_t*>(
+                inputData->mNumberBuffers > 1 ? inputData->mBuffers[1].mData
+                                              : inputData->mBuffers[0].mData);
+
+            for (UInt32 frameIndex = 0; frameIndex < frames; ++frameIndex) {
+                chunk.left[frameIndex] =
+                    readSampleFromFormat(leftData, format, frameIndex);
+                chunk.right[frameIndex] = inputData->mNumberBuffers > 1
+                    ? readSampleFromFormat(rightData, format, frameIndex)
+                    : chunk.left[frameIndex];
+            }
+        }
+
+        {
+            std::lock_guard<std::mutex> queueLock(chunkMutex_);
+            if (chunkQueue_.size() >= kMaxQueuedChunks) {
+                chunkQueue_.pop_front();
+                ++overwriteCount_;
+            }
+            chunkQueue_.push_back(std::move(chunk));
+        }
+
+        return noErr;
+    }
+
+    bool startInternal(const std::string& requestedDeviceUid, std::string* outErrorMessage) {
+        std::lock_guard<std::mutex> lock(stateMutex_);
+        stopLocked();
+
+        if (!isSupported()) {
+            if (outErrorMessage != nullptr) {
+                *outErrorMessage =
+                    "Native output-device capture requires macOS 14.2 or newer.";
+            }
+            return false;
+        }
+
+        const auto devices = enumerateOutputDevices();
+        if (devices.empty()) {
+            if (outErrorMessage != nullptr) {
+                *outErrorMessage = "No macOS output devices are available.";
+            }
+            return false;
+        }
+
+        const OutputDeviceInfo* selected = nullptr;
+        if (!requestedDeviceUid.empty()) {
+            for (const auto& device : devices) {
+                if (device.uid == requestedDeviceUid) {
+                    selected = &device;
+                    break;
+                }
+            }
+            if (selected == nullptr) {
+                if (outErrorMessage != nullptr) {
+                    *outErrorMessage =
+                        "The selected macOS output device is no longer available.";
+                }
+                return false;
+            }
+        } else {
+            for (const auto& device : devices) {
+                if (device.isDefault) {
+                    selected = &device;
+                    break;
+                }
+            }
+            if (selected == nullptr) {
+                selected = &devices.front();
+            }
+        }
+
+        if (@available(macOS 14.2, *)) {
+            @autoreleasepool {
+                NSString* deviceUID = toNSString(selected->uid);
+                NSString* deviceLabel = toNSString(selected->label);
+                NSArray<NSNumber*>* excludedProcesses = @[];
+                CATapDescription* tapDescription =
+                    [[CATapDescription alloc] initExcludingProcesses:excludedProcesses
+                                                         andDeviceUID:deviceUID
+                                                           withStream:0];
+                tapDescription.name = [NSString stringWithFormat:@"Prism Tap %@", deviceLabel];
+                tapDescription.UUID = [NSUUID UUID];
+                tapDescription.privateTap = YES;
+                tapDescription.muteBehavior = CATapUnmuted;
+
+                const OSStatus tapStatus =
+                    AudioHardwareCreateProcessTap(tapDescription, &tapId_);
+                if (tapStatus != noErr) {
+                    if (outErrorMessage != nullptr) {
+                        *outErrorMessage =
+                            formatStatusMessage("AudioHardwareCreateProcessTap", tapStatus);
+                    }
+                    tapId_ = kUnknownObject;
+                    return false;
+                }
+
+                NSString* aggregateUID = [NSString
+                    stringWithFormat:@"com.astra.prism.capture.%@", [NSUUID UUID].UUIDString];
+                NSDictionary* aggregateDescription = @{
+                    [NSString stringWithUTF8String:kAudioAggregateDeviceNameKey]:
+                        [NSString stringWithFormat:@"Prism Capture %@", deviceLabel],
+                    [NSString stringWithUTF8String:kAudioAggregateDeviceUIDKey]: aggregateUID,
+                    [NSString stringWithUTF8String:kAudioAggregateDeviceIsPrivateKey]: @YES,
+                    [NSString stringWithUTF8String:kAudioAggregateDeviceMainSubDeviceKey]:
+                        deviceUID,
+                    [NSString stringWithUTF8String:kAudioAggregateDeviceTapAutoStartKey]: @YES,
+                    [NSString stringWithUTF8String:kAudioAggregateDeviceSubDeviceListKey]: @[
+                        @{
+                            [NSString stringWithUTF8String:kAudioSubDeviceUIDKey]: deviceUID,
+                            [NSString stringWithUTF8String:kAudioSubDeviceNameKey]: deviceLabel,
+                            [NSString stringWithUTF8String:kAudioSubDeviceDriftCompensationKey]:
+                                @YES,
+                            [NSString
+                                stringWithUTF8String:kAudioSubDeviceDriftCompensationQualityKey]:
+                                @(kAudioAggregateDriftCompensationMediumQuality),
+                        }
+                    ],
+                    [NSString stringWithUTF8String:kAudioAggregateDeviceTapListKey]: @[
+                        @{
+                            [NSString stringWithUTF8String:kAudioSubTapUIDKey]:
+                                tapDescription.UUID.UUIDString,
+                            [NSString stringWithUTF8String:kAudioSubTapDriftCompensationKey]:
+                                @YES,
+                            [NSString
+                                stringWithUTF8String:kAudioSubTapDriftCompensationQualityKey]:
+                                @(kAudioAggregateDriftCompensationMediumQuality),
+                        }
+                    ],
+                };
+
+                const OSStatus aggregateStatus = AudioHardwareCreateAggregateDevice(
+                    (__bridge CFDictionaryRef)aggregateDescription, &aggregateDeviceId_);
+                if (aggregateStatus != noErr) {
+                    if (outErrorMessage != nullptr) {
+                        *outErrorMessage = formatStatusMessage(
+                            "AudioHardwareCreateAggregateDevice", aggregateStatus);
+                    }
+                    AudioHardwareDestroyProcessTap(tapId_);
+                    tapId_ = kUnknownObject;
+                    aggregateDeviceId_ = kUnknownObject;
+                    return false;
+                }
+            }
+        }
+
+        if (!getTapFormat(tapId_, &tapFormat_)) {
+            tapFormat_ = AudioStreamBasicDescription{};
+            tapFormat_.mSampleRate = selected->sampleRate;
+            tapFormat_.mChannelsPerFrame = std::max<UInt32>(2, selected->channelCount);
+            tapFormat_.mBitsPerChannel = 32;
+            tapFormat_.mBytesPerFrame =
+                tapFormat_.mChannelsPerFrame * sizeof(Float32);
+            tapFormat_.mFramesPerPacket = 1;
+            tapFormat_.mBytesPerPacket =
+                tapFormat_.mBytesPerFrame * tapFormat_.mFramesPerPacket;
+            tapFormat_.mFormatID = kAudioFormatLinearPCM;
+            tapFormat_.mFormatFlags = kAudioFormatFlagIsFloat | kAudioFormatFlagIsPacked;
+        }
+
+        const OSStatus ioProcStatus =
+            AudioDeviceCreateIOProcID(aggregateDeviceId_, StaticIOProc, this, &ioProcId_);
+        if (ioProcStatus != noErr) {
+            if (outErrorMessage != nullptr) {
+                *outErrorMessage =
+                    formatStatusMessage("AudioDeviceCreateIOProcID", ioProcStatus);
+            }
+            stopLocked();
+            return false;
+        }
+
+        const OSStatus startStatus = AudioDeviceStart(aggregateDeviceId_, ioProcId_);
+        if (startStatus != noErr) {
+            if (outErrorMessage != nullptr) {
+                *outErrorMessage = formatStatusMessage("AudioDeviceStart", startStatus);
+            }
+            stopLocked();
+            return false;
+        }
+
+        {
+            std::lock_guard<std::mutex> queueLock(chunkMutex_);
+            chunkQueue_.clear();
+            overwriteCount_ = 0;
+        }
+
+        active_ = true;
+        activeDeviceUid_ = selected->uid;
+        activeDeviceLabel_ = selected->label;
+        sampleRate_ = tapFormat_.mSampleRate > 0 ? tapFormat_.mSampleRate : selected->sampleRate;
+        channelCount_ =
+            std::max<UInt32>(1, tapFormat_.mChannelsPerFrame > 0 ? tapFormat_.mChannelsPerFrame
+                                                                 : selected->channelCount);
+        sequence_ = 0;
+        return true;
+    }
+
+    void stopLocked() {
+        active_ = false;
+
+        if (aggregateDeviceId_ != kUnknownObject && ioProcId_ != nullptr) {
+            AudioDeviceStop(aggregateDeviceId_, ioProcId_);
+            AudioDeviceDestroyIOProcID(aggregateDeviceId_, ioProcId_);
+            ioProcId_ = nullptr;
+        }
+
+        if (aggregateDeviceId_ != kUnknownObject) {
+            AudioHardwareDestroyAggregateDevice(aggregateDeviceId_);
+            aggregateDeviceId_ = kUnknownObject;
+        }
+
+        if (tapId_ != kUnknownObject) {
+            if (@available(macOS 14.2, *)) {
+                AudioHardwareDestroyProcessTap(tapId_);
+            }
+            tapId_ = kUnknownObject;
+        }
+
+        tapFormat_ = AudioStreamBasicDescription{};
+        activeDeviceUid_.clear();
+        activeDeviceLabel_.clear();
+        sampleRate_ = 48000.0;
+        channelCount_ = 2;
+        sequence_ = 0;
+
+        std::lock_guard<std::mutex> queueLock(chunkMutex_);
+        chunkQueue_.clear();
+        overwriteCount_ = 0;
+    }
+
+    bool isSupported() const {
+        if (@available(macOS 14.2, *)) {
+            return true;
+        }
+        return false;
+    }
+
+    mutable std::mutex stateMutex_;
+    std::mutex chunkMutex_;
+    std::deque<CapturedChunk> chunkQueue_;
+    uint64_t overwriteCount_ = 0;
+    uint64_t sequence_ = 0;
+
+    AudioObjectID tapId_ = kUnknownObject;
+    AudioObjectID aggregateDeviceId_ = kUnknownObject;
+    AudioDeviceIOProcID ioProcId_ = nullptr;
+    AudioStreamBasicDescription tapFormat_{};
+
+    bool active_ = false;
+    std::string activeDeviceUid_;
+    std::string activeDeviceLabel_;
+    double sampleRate_ = 48000.0;
+    UInt32 channelCount_ = 2;
+};
+
+MacOSNativeCaptureEngine& engine() {
+    static MacOSNativeCaptureEngine instance;
+    return instance;
+}
+
+Napi::Value MacOSGetSupport(const Napi::CallbackInfo& info) {
+    return engine().GetSupport(info.Env());
+}
+
+Napi::Value MacOSListOutputDevices(const Napi::CallbackInfo& info) {
+    return engine().ListOutputDevices(info.Env());
+}
+
+Napi::Value MacOSStart(const Napi::CallbackInfo& info) {
+    std::string requestedDeviceUid;
+    if (info.Length() >= 1 && info[0].IsString()) {
+        requestedDeviceUid = info[0].As<Napi::String>().Utf8Value();
+    }
+    return engine().Start(info.Env(), requestedDeviceUid);
+}
+
+Napi::Value MacOSStop(const Napi::CallbackInfo& info) {
+    engine().Stop();
+    return info.Env().Undefined();
+}
+
+Napi::Value MacOSDrain(const Napi::CallbackInfo& info) {
+    size_t maxChunks = kDefaultDrainChunkLimit;
+    if (info.Length() >= 1 && info[0].IsNumber()) {
+        const int64_t requested = info[0].As<Napi::Number>().Int64Value();
+        if (requested > 0) {
+            maxChunks = static_cast<size_t>(requested);
+        }
+    }
+    return engine().Drain(info.Env(), maxChunks);
+}
+
+Napi::Value MacOSNowMilliseconds(const Napi::CallbackInfo& info) {
+    return Napi::Number::New(info.Env(), engine().NowMilliseconds());
+}
+
+}  // namespace
+
+void RegisterMacOSCapture(Napi::Env env, Napi::Object exports) {
+    Napi::Object captureExports = Napi::Object::New(env);
+    captureExports.Set("getSupport", Napi::Function::New(env, MacOSGetSupport));
+    captureExports.Set(
+        "listOutputDevices", Napi::Function::New(env, MacOSListOutputDevices));
+    captureExports.Set("start", Napi::Function::New(env, MacOSStart));
+    captureExports.Set("stop", Napi::Function::New(env, MacOSStop));
+    captureExports.Set("drain", Napi::Function::New(env, MacOSDrain));
+    captureExports.Set(
+        "nowMilliseconds", Napi::Function::New(env, MacOSNowMilliseconds));
+    exports.Set("macosCapture", captureExports);
+}
+
+#endif  // defined(__APPLE__)

native/src/macos_capture_stub.cpp

@@ -0,0 +1,54 @@
+#include "macos_capture.h"
+
+namespace {
+
+Napi::Value GetSupport(const Napi::CallbackInfo& info) {
+    Napi::Object support = Napi::Object::New(info.Env());
+    support.Set("available", Napi::Boolean::New(info.Env(), false));
+    support.Set(
+        "reason",
+        Napi::String::New(
+            info.Env(), "Native macOS output-device capture is unavailable on this platform."));
+    return support;
+}
+
+Napi::Value ListOutputDevices(const Napi::CallbackInfo& info) {
+    return Napi::Array::New(info.Env());
+}
+
+Napi::Value Start(const Napi::CallbackInfo& info) {
+    Napi::Error::New(
+        info.Env(), "Native macOS output-device capture is unavailable on this platform.")
+        .ThrowAsJavaScriptException();
+    return info.Env().Undefined();
+}
+
+Napi::Value Stop(const Napi::CallbackInfo& info) {
+    return info.Env().Undefined();
+}
+
+Napi::Value Drain(const Napi::CallbackInfo& info) {
+    Napi::Object result = Napi::Object::New(info.Env());
+    result.Set("chunks", Napi::Array::New(info.Env()));
+    result.Set("overwriteCount", Napi::Number::New(info.Env(), 0));
+    result.Set("queueDepth", Napi::Number::New(info.Env(), 0));
+    return result;
+}
+
+Napi::Value NowMilliseconds(const Napi::CallbackInfo& info) {
+    return Napi::Number::New(info.Env(), 0);
+}
+
+}  // namespace
+
+void RegisterMacOSCapture(Napi::Env env, Napi::Object exports) {
+    Napi::Object captureExports = Napi::Object::New(env);
+    captureExports.Set("getSupport", Napi::Function::New(env, GetSupport));
+    captureExports.Set(
+        "listOutputDevices", Napi::Function::New(env, ListOutputDevices));
+    captureExports.Set("start", Napi::Function::New(env, Start));
+    captureExports.Set("stop", Napi::Function::New(env, Stop));
+    captureExports.Set("drain", Napi::Function::New(env, Drain));
+    captureExports.Set("nowMilliseconds", Napi::Function::New(env, NowMilliseconds));
+    exports.Set("macosCapture", captureExports);
+}

native/src/main.cpp

@@ -1,5 +1,6 @@
 #include <napi.h>
 #include <cstring>
+#include "macos_capture.h"
 #include "oscilloscope.h"
 #include "spectrum.h"
 #include "vectorscope.h"
@@ -294,6 +295,8 @@ Napi::Object Init(Napi::Env env, Napi::Object exports) {
     vecExports.Set("reset", Napi::Function::New(env, VectorscopeReset));
     exports.Set("vectorscope", vecExports);
 
+    RegisterMacOSCapture(env, exports);
+
     return exports;
 }
 

src/preload/index.ts

@@ -1,5 +1,9 @@
 import { contextBridge, ipcRenderer } from 'electron'
-import type { CaptureBackendSupport } from '../types/capture'
+import type { CaptureBackendSupport, CaptureBackendSupportEntry } from '../types/capture'
+import type { NativeCaptureAPI } from '../types/nativeCapture'
+import type { VisualizerDSP } from '../renderer/audio/native/visualizer-dsp'
+
+type NativeAddonModule = VisualizerDSP & NativeCaptureAPI
 
 // Expose Electron API to renderer
 contextBridge.exposeInMainWorld('electronAPI', {
@@ -9,7 +13,13 @@ contextBridge.exposeInMainWorld('electronAPI', {
   toggleAlwaysOnTop: () => ipcRenderer.send('window:toggle-always-on-top'),
   isAlwaysOnTop: () => ipcRenderer.invoke('window:is-always-on-top'),
   getDesktopSources: () => ipcRenderer.invoke('audio:get-desktop-sources') as Promise<{ id: string; name: string }[]>,
-  getCaptureBackendSupport: () => ipcRenderer.invoke('capture:get-backend-support') as Promise<CaptureBackendSupport>,
+  getCaptureBackendSupport: async () => {
+    const support = await ipcRenderer.invoke('capture:get-backend-support') as CaptureBackendSupport
+    return {
+      ...support,
+      nativeBackend: resolveNativeCaptureSupport(support.nativeBackend),
+    } satisfies CaptureBackendSupport
+  },
   expandSettings: (panelHeight: number) => ipcRenderer.send('window:expand-settings', panelHeight),
   collapseSettings: (panelHeight: number) => ipcRenderer.send('window:collapse-settings', panelHeight),
   setSettingsHeight: (panelHeight: number) => ipcRenderer.send('window:set-settings-height', panelHeight),
@@ -36,15 +46,54 @@ contextBridge.exposeInMainWorld('electronAPI', {
 })
 
 // Native DSP module — load if available, gracefully degrade if not
-let visualizerDSP: unknown = null
+let nativeAddonModule: NativeAddonModule | null = null
 try {
   const isDev = process.env.NODE_ENV === 'development'
   const modulePath = isDev
     ? require('path').join(__dirname, '../../native/build/Release/visualizer_dsp.node')
     : require('path').join(process.resourcesPath!, 'native/visualizer_dsp.node')
-  visualizerDSP = require(modulePath)
+  nativeAddonModule = require(modulePath) as NativeAddonModule
 } catch {
   console.warn('Native DSP module not available — using JS fallback')
 }
 
-contextBridge.exposeInMainWorld('visualizerAPI', visualizerDSP)
+function resolveNativeCaptureSupport(
+  fallbackEntry: CaptureBackendSupportEntry,
+): CaptureBackendSupportEntry {
+  if (process.platform !== 'darwin') {
+    return fallbackEntry
+  }
+
+  const macosCapture = nativeAddonModule?.macosCapture
+  if (!macosCapture) {
+    return {
+      kind: 'native-macos',
+      available: false,
+      reason: 'Native capture module is not available in this build.',
+    }
+  }
+
+  const support = macosCapture.getSupport()
+  return {
+    kind: 'native-macos',
+    available: support.available,
+    reason: support.reason,
+  }
+}
+
+const visualizerAPI = nativeAddonModule
+  ? {
+      oscilloscope: nativeAddonModule.oscilloscope,
+      spectrum: nativeAddonModule.spectrum,
+      vectorscope: nativeAddonModule.vectorscope,
+    }
+  : null
+
+const nativeCaptureAPI = nativeAddonModule
+  ? {
+      macosCapture: nativeAddonModule.macosCapture,
+    }
+  : null
+
+contextBridge.exposeInMainWorld('visualizerAPI', visualizerAPI)
+contextBridge.exposeInMainWorld('nativeCaptureAPI', nativeCaptureAPI)

src/renderer/audio/AudioCapture.ts

@@ -13,6 +13,7 @@ import type {
   CaptureMode,
   CaptureSourceDescriptor,
 } from '../../types/capture'
+import type { NativeMacOSCaptureDrainResult, NativeMacOSCaptureStartResult } from '../../types/nativeCapture'
 
 export type { CaptureMode } from '../../types/capture'
 
@@ -60,6 +61,7 @@ export interface CaptureManagerStatus {
 type StatusListener = (status: CaptureManagerStatus) => void
 
 const DEFAULT_BACKEND_POLICY: CaptureBackendPolicy = 'auto'
+const DEFAULT_SYSTEM_SOURCE_ID = '__default_system_output__'
 
 const DEFAULT_BACKEND_SUPPORT: CaptureBackendSupport = {
   policyOptions: ['auto', 'native', 'electron'],
@@ -92,6 +94,15 @@ function toDeviceSourceDescriptor(device: MediaDeviceInfo): CaptureSourceDescrip
   }
 }
 
+function getDefaultSystemSourceDescriptor(): CaptureSourceDescriptor {
+  return {
+    id: DEFAULT_SYSTEM_SOURCE_ID,
+    label: 'System Output',
+    kind: 'system',
+    isDefault: true,
+  }
+}
+
 class ElectronCaptureRuntime {
   private audioContext: AudioContext | null = null
   private stream: MediaStream | null = null
@@ -128,12 +139,7 @@ class ElectronCaptureRuntime {
   }
 
   async listSystemSources(): Promise<CaptureSourceDescriptor[]> {
-    const sources = await window.electronAPI.getDesktopSources()
-    return sources.map((source) => ({
-      id: source.id,
-      label: source.name,
-      kind: 'system',
-    }))
+    return [getDefaultSystemSourceDescriptor()]
   }
 
   async listDeviceSources(): Promise<CaptureSourceDescriptor[]> {
@@ -332,6 +338,142 @@ class ElectronDeviceCaptureBackend implements CaptureBackend {
   }
 }
 
+class NativeMacOSCaptureBackend implements CaptureBackend {
+  readonly kind = 'native-macos' as const
+
+  private readonly chunkListeners = new Set<(chunk: CaptureChunk) => void>()
+  private pollTimer: number | null = null
+  private active = false
+  private sampleRate = 48000
+  private channelCount = 2
+  private supportReason: string | null
+  private performanceOffsetMilliseconds = 0
+
+  constructor(private readonly supportEntry: CaptureBackendSupportEntry) {
+    this.supportReason = supportEntry.reason
+  }
+
+  async start(request?: CaptureBackendStartRequest): Promise<void> {
+    const nativeCapture = window.nativeCaptureAPI?.macosCapture
+    if (!nativeCapture) {
+      throw new Error('Native macOS capture module is not available in this build.')
+    }
+
+    const support = nativeCapture.getSupport()
+    if (!support.available) {
+      throw new Error(support.reason ?? 'Native macOS capture is unavailable.')
+    }
+
+    const nativeNow = nativeCapture.nowMilliseconds()
+    this.performanceOffsetMilliseconds = performance.now() - nativeNow
+
+    const startResult = nativeCapture.start(
+      request?.deviceId && request.deviceId !== DEFAULT_SYSTEM_SOURCE_ID
+        ? request.deviceId
+        : undefined,
+    ) as NativeMacOSCaptureStartResult
+
+    this.sampleRate = Math.max(1, Math.floor(startResult.sampleRate) || 48000)
+    this.channelCount = Math.max(1, Math.floor(startResult.channelCount) || 2)
+    this.supportReason = null
+    this.active = true
+    this.startPolling()
+  }
+
+  async stop(): Promise<void> {
+    this.stopPolling()
+    window.nativeCaptureAPI?.macosCapture.stop()
+    this.active = false
+  }
+
+  async listSources(): Promise<CaptureSourceDescriptor[]> {
+    const nativeCapture = window.nativeCaptureAPI?.macosCapture
+    if (!nativeCapture) {
+      return [getDefaultSystemSourceDescriptor()]
+    }
+
+    const support = nativeCapture.getSupport()
+    if (!support.available) {
+      return [getDefaultSystemSourceDescriptor()]
+    }
+
+    const sources = nativeCapture.listOutputDevices()
+    if (!sources.length) {
+      return [getDefaultSystemSourceDescriptor()]
+    }
+
+    return sources.map((source) => ({
+      id: source.id,
+      label: source.label,
+      kind: 'system',
+      isDefault: source.isDefault,
+      sampleRate: source.sampleRate,
+      channelCount: source.channelCount,
+    }))
+  }
+
+  subscribe(listener: (chunk: CaptureChunk) => void): () => void {
+    this.chunkListeners.add(listener)
+    return () => {
+      this.chunkListeners.delete(listener)
+    }
+  }
+
+  getStatus(): CaptureBackendStatus {
+    return {
+      kind: this.kind,
+      active: this.active,
+      available: this.supportEntry.available,
+      reason: this.supportReason,
+      sampleRate: this.sampleRate,
+      channelCount: this.channelCount,
+    }
+  }
+
+  private startPolling(): void {
+    this.stopPolling()
+
+    const poll = (): void => {
+      if (!this.active) return
+
+      try {
+        const result = window.nativeCaptureAPI?.macosCapture.drain(32) as NativeMacOSCaptureDrainResult | undefined
+        if (result) {
+          for (const chunk of result.chunks) {
+            const routedChunk: CaptureChunk = {
+              left: chunk.left,
+              right: chunk.right,
+              channelCount: Math.max(1, Math.floor(chunk.channelCount) || 1),
+              capturedAt: chunk.capturedAtMilliseconds + this.performanceOffsetMilliseconds,
+              sequence: Math.max(1, Math.floor(chunk.sequence) || 1),
+            }
+
+            for (const listener of this.chunkListeners) {
+              listener(routedChunk)
+            }
+          }
+        }
+      } catch (error) {
+        console.error('Native macOS capture poll failed:', error)
+        this.active = false
+        this.stopPolling()
+        return
+      }
+
+      this.pollTimer = window.setTimeout(poll, 4)
+    }
+
+    this.pollTimer = window.setTimeout(poll, 0)
+  }
+
+  private stopPolling(): void {
+    if (this.pollTimer !== null) {
+      window.clearTimeout(this.pollTimer)
+      this.pollTimer = null
+    }
+  }
+}
+
 class NativeUnavailableCaptureBackend implements CaptureBackend {
   readonly kind: CaptureBackendKind
   private readonly reason: string | null
@@ -380,6 +522,7 @@ class AudioCapture {
   private activeBackend: CaptureBackend | null = null
 
   private selectedDeviceId: string | null = null
+  private selectedSystemSourceId: string | null = DEFAULT_SYSTEM_SOURCE_ID
   private captureMode: CaptureMode = 'system'
   private backendPolicy: CaptureBackendPolicy = DEFAULT_BACKEND_POLICY
   private activeBackendReason: string | null = null
@@ -403,12 +546,16 @@ class AudioCapture {
   }
 
   async refreshBackendSupport(): Promise<CaptureBackendSupport> {
+    this.backendSupport = null
     this.backendSupportPromise = null
     return this.ensureBackendSupport()
   }
 
-  async startSystemAudio(): Promise<void> {
+  async startSystemAudio(sourceId?: string): Promise<void> {
     this.captureMode = 'system'
+    if (sourceId) {
+      this.selectedSystemSourceId = sourceId
+    }
     await this.start()
   }
 
@@ -428,9 +575,13 @@ class AudioCapture {
 
     const support = await this.ensureBackendSupport()
     const requestedMode = this.captureMode
-    const requestedDeviceId = requestedMode === 'device' ? this.selectedDeviceId ?? undefined : undefined
+    const requestedDeviceId = requestedMode === 'device'
+      ? this.selectedDeviceId ?? undefined
+      : this.selectedSystemSourceId ?? DEFAULT_SYSTEM_SOURCE_ID
     const candidateBackends = this.resolveCandidateBackends(support, requestedMode)
 
+    await this.stopActiveCapture()
+
     let lastError: Error | null = null
     let nativeFallbackReason: string | null = null
 
@@ -462,15 +613,7 @@ class AudioCapture {
   }
 
   stop(): void {
-    if (this.sessionId !== null) {
-      audioRouter.endSession()
-      this.sessionId = null
-    }
-
-    if (this.activeBackend) {
-      void this.activeBackend.stop()
-    }
-
+    void this.stopActiveCapture()
     this.emitStatus()
   }
 
@@ -481,7 +624,8 @@ class AudioCapture {
     }
 
     const activeSystemBackend = this.resolveCandidateBackends(this.backendSupport ?? DEFAULT_BACKEND_SUPPORT, 'system')[0]
-    return activeSystemBackend.listSources()
+    const sources = await activeSystemBackend.listSources()
+    return sources.length ? sources : [getDefaultSystemSourceDescriptor()]
   }
 
   async listDevices(): Promise<MediaDeviceInfo[]> {
@@ -498,6 +642,15 @@ class AudioCapture {
     this.emitStatus()
   }
 
+  getSelectedSystemSourceId(): string | null {
+    return this.selectedSystemSourceId
+  }
+
+  setSelectedSystemSourceId(id: string | null): void {
+    this.selectedSystemSourceId = id ?? DEFAULT_SYSTEM_SOURCE_ID
+    this.emitStatus()
+  }
+
   getCaptureMode(): CaptureMode {
     return this.captureMode
   }
@@ -544,7 +697,7 @@ class AudioCapture {
         .catch(() => DEFAULT_BACKEND_SUPPORT)
         .then((support) => {
           this.backendSupport = support
-          this.nativeBackend = new NativeUnavailableCaptureBackend(support.nativeBackend)
+          this.nativeBackend = this.createNativeBackend(support.nativeBackend)
           this.emitStatus()
           return support
         })
@@ -577,6 +730,28 @@ class AudioCapture {
     }
   }
 
+  private createNativeBackend(supportEntry: CaptureBackendSupportEntry): CaptureBackend {
+    const backend = supportEntry.kind === 'native-macos' && supportEntry.available
+      ? new NativeMacOSCaptureBackend(supportEntry)
+      : new NativeUnavailableCaptureBackend(supportEntry)
+
+    backend.subscribe((chunk) => this.handleChunk(backend.kind, chunk))
+    return backend
+  }
+
+  private async stopActiveCapture(): Promise<void> {
+    if (this.sessionId !== null) {
+      audioRouter.endSession()
+      this.sessionId = null
+    }
+
+    if (this.activeBackend) {
+      const backend = this.activeBackend
+      this.activeBackend = null
+      await backend.stop()
+    }
+  }
+
   private handleChunk(originKind: CaptureBackendKind, chunk: CaptureChunk): void {
     if (!this.activeBackend || this.activeBackend.kind !== originKind || this.sessionId === null) {
       return

src/renderer/components/SettingsPanel.tsx

@@ -1,11 +1,9 @@
-import { useEffect, useMemo, useRef, useState, type CSSProperties, type JSX, type ReactNode } from 'react'
+import { useEffect, useMemo, useRef, type CSSProperties, type JSX, type ReactNode } from 'react'
 import { useAudioStore } from '../stores/audioStore'
 import { useSettingsStore, type ScopeSettings } from '../stores/settingsStore'
 import { useThemeStore, PRESETS, PRESET_IDS } from '../stores/themeStore'
 import type { ScopeKind } from '../../types/scope'
 import { buildAnalyzerGridTemplateColumns } from '../analyzerLayout'
-import { audioRouter, type AudioRouterDiagnostics } from '../audio/AudioRouter'
-import type { CaptureBackendKind, CaptureBackendPolicy } from '../../types/capture'
 
 const SCOPE_LABELS: Record<ScopeKind, string> = {
   spectrum: 'Spectrum',
@@ -17,23 +15,6 @@ const SCOPE_LABELS: Record<ScopeKind, string> = {
   waveform: 'Waveform',
 }
 
-function captureBackendLabel(kind: CaptureBackendKind | null): string {
-  switch (kind) {
-    case 'electron-system':
-      return 'Electron System'
-    case 'electron-device':
-      return 'Electron Device'
-    case 'native-macos':
-      return 'Native macOS'
-    case 'native-windows':
-      return 'Native Windows'
-    case 'native-linux':
-      return 'Native Linux'
-    default:
-      return 'None'
-  }
-}
-
 function vectorscopeModeLabel(mode: ScopeSettings['vectorscope']['mode']): string {
   switch (mode) {
     case 'lissajous':
@@ -496,30 +477,29 @@ interface SettingsPanelProps {
 
 export default function SettingsPanel({ onClose, onHeightChange }: SettingsPanelProps): JSX.Element {
   const {
+    systemSources,
     devices,
+    selectedSystemSourceId,
     selectedDeviceId,
     captureMode,
-    capturePolicy,
-    activeBackendKind,
-    activeBackendReason,
     isCapturing,
     captureStatus,
     captureError,
+    refreshSystemSources,
     refreshDevices,
     refreshBackendSupport,
+    selectSystemSource,
     selectDevice,
-    setCaptureMode,
-    setCapturePolicy,
     startCapture,
   } = useAudioStore()
   const { scopeSettings, updateScopeSettings, hiddenScopes, scopeOrder, widthWeights } = useSettingsStore()
   const { presetId, accent, setPreset, setCustomAccent, customAccent } = useThemeStore()
   const panelRef = useRef<HTMLDivElement | null>(null)
-  const [routerDiagnostics, setRouterDiagnostics] = useState<AudioRouterDiagnostics>(
-    () => audioRouter.getDiagnosticsSnapshot(),
-  )
 
-  const visibleScopes = scopeOrder.filter((kind) => !hiddenScopes.has(kind))
+  const visibleScopes = useMemo(
+    () => scopeOrder.filter((kind) => !hiddenScopes.has(kind)),
+    [scopeOrder, hiddenScopes],
+  )
   const scopeTrackStyle = useMemo(() => {
     const gridTemplateColumns = buildAnalyzerGridTemplateColumns(visibleScopes, widthWeights)
     if (!gridTemplateColumns) return undefined
@@ -527,18 +507,10 @@ export default function SettingsPanel({ onClose, onHeightChange }: SettingsPanel
   }, [visibleScopes, widthWeights])
 
   useEffect(() => {
-    void Promise.all([refreshDevices(), refreshBackendSupport()])
-  }, [refreshBackendSupport, refreshDevices])
-
-  useEffect(() => {
-    const intervalId = window.setInterval(() => {
-      setRouterDiagnostics(audioRouter.getDiagnosticsSnapshot())
-    }, 250)
-
-    return () => {
-      window.clearInterval(intervalId)
-    }
-  }, [])
+    void refreshBackendSupport()
+    void refreshSystemSources()
+    void refreshDevices()
+  }, [refreshBackendSupport, refreshSystemSources, refreshDevices])
 
   useEffect(() => {
     const panel = panelRef.current
@@ -565,19 +537,36 @@ export default function SettingsPanel({ onClose, onHeightChange }: SettingsPanel
   }, [onHeightChange, visibleScopes.length])
 
   const handleSourceChange = async (value: string): Promise<void> => {
-    if (value === '__system__') {
-      setCaptureMode('system')
+    if (value.startsWith('system:')) {
+      const sourceId = value.slice('system:'.length)
+      await selectSystemSource(sourceId)
       await startCapture()
       return
     }
 
-    await selectDevice(value)
-    await startCapture()
+    if (value.startsWith('device:')) {
+      const deviceId = value.slice('device:'.length)
+      await selectDevice(deviceId)
+      await startCapture()
+    }
   }
 
-  const handlePolicyChange = async (value: string): Promise<void> => {
-    await setCapturePolicy(value as CaptureBackendPolicy)
-  }
+  const selectedSourceValue = captureMode === 'system'
+    ? `system:${selectedSystemSourceId ?? systemSources[0]?.id ?? '__default_system_output__'}`
+    : `device:${selectedDeviceId ?? ''}`
+
+  const visibleSystemSources = systemSources.length
+    ? systemSources
+    : [{ id: '__default_system_output__', label: 'System Output', kind: 'system', isDefault: true }]
+
+  const showInputDevices = devices.length > 0
+
+  const renderSystemSourceLabel = (label: string, isDefault?: boolean): string => (
+    isDefault ? `${label} (Default)` : label
+  )
+
+  const renderInputDeviceValue = (deviceId: string): string => `device:${deviceId}`
+  const renderSystemSourceValue = (sourceId: string): string => `system:${sourceId}`
 
   const indicatorLabel = isCapturing
     ? 'Capturing'
@@ -587,10 +576,6 @@ export default function SettingsPanel({ onClose, onHeightChange }: SettingsPanel
         ? 'Capture Failed'
         : 'Idle'
 
-  const latencyLabel = routerDiagnostics.overallP95CaptureToScopeMs === null
-    ? 'Waiting for samples'
-    : `${routerDiagnostics.overallP95CaptureToScopeMs.toFixed(1)} ms p95`
-
   return (
     <div className="settings-panel" ref={panelRef}>
       <div className="settings-panel__utility-row">
@@ -601,34 +586,27 @@ export default function SettingsPanel({ onClose, onHeightChange }: SettingsPanel
             <span className="settings-control__label">Source</span>
             <select
               className="settings-control__select"
-              value={captureMode === 'system' ? '__system__' : selectedDeviceId ?? ''}
+              value={selectedSourceValue}
               onChange={(event) => {
                 void handleSourceChange(event.target.value)
               }}
             >
-              <option value="__system__">System Audio</option>
-              <optgroup label="Devices">
-                {devices.map((device) => (
-                  <option key={device.deviceId} value={device.deviceId}>
-                    {device.label || `Input ${device.deviceId.slice(0, 8)}`}
+              <optgroup label="Output Devices">
+                {visibleSystemSources.map((source) => (
+                  <option key={source.id} value={renderSystemSourceValue(source.id)}>
+                    {renderSystemSourceLabel(source.label, source.isDefault)}
                   </option>
                 ))}
               </optgroup>
-            </select>
-          </label>
-
-          <label className="settings-control settings-control--stack">
-            <span className="settings-control__label">Backend Policy</span>
-            <select
-              className="settings-control__select"
-              value={capturePolicy}
-              onChange={(event) => {
-                void handlePolicyChange(event.target.value)
-              }}
-            >
-              <option value="auto">Auto</option>
-              <option value="native">Native</option>
-              <option value="electron">Electron</option>
+              {showInputDevices ? (
+                <optgroup label="Input Devices">
+                  {devices.map((device) => (
+                    <option key={device.deviceId} value={renderInputDeviceValue(device.deviceId)}>
+                      {device.label || `Input ${device.deviceId.slice(0, 8)}`}
+                    </option>
+                  ))}
+                </optgroup>
+              ) : null}
             </select>
           </label>
 
@@ -637,18 +615,6 @@ export default function SettingsPanel({ onClose, onHeightChange }: SettingsPanel
             <span>{indicatorLabel}</span>
           </div>
 
-          <div className="settings-info-text">
-            Active backend: {captureBackendLabel(activeBackendKind)}
-          </div>
-
-          <div className="settings-info-text">
-            Latency probe: {latencyLabel} · overwrites {routerDiagnostics.totalOverwriteCount} · stale drops {routerDiagnostics.staleSessionDrops}
-          </div>
-
-          {activeBackendReason ? (
-            <div className="settings-info-text">{activeBackendReason}</div>
-          ) : null}
-
           {captureError ? (
             <div className="settings-error-text">{captureError}</div>
           ) : null}

src/renderer/env.d.ts

@@ -2,10 +2,12 @@
 
 import type { VisualizerDSP } from './audio/native/visualizer-dsp'
 import type { CaptureBackendSupport } from '../types/capture'
+import type { NativeCaptureAPI } from '../types/nativeCapture'
 
 declare global {
   interface Window {
     visualizerAPI: VisualizerDSP | null
+    nativeCaptureAPI: NativeCaptureAPI | null
     electronAPI: {
       platform: string
       minimize: () => void

src/renderer/stores/audioStore.ts

@@ -5,10 +5,13 @@ import type {
   CaptureBackendPolicy,
   CaptureBackendSupport,
   CaptureMode,
+  CaptureSourceDescriptor,
 } from '../../types/capture'
 
 interface AudioState {
+  systemSources: CaptureSourceDescriptor[]
   devices: MediaDeviceInfo[]
+  selectedSystemSourceId: string | null
   selectedDeviceId: string | null
   captureMode: CaptureMode
   capturePolicy: CaptureBackendPolicy
@@ -20,8 +23,10 @@ interface AudioState {
   captureError: string | null
   sampleRate: number
   channelCount: number
+  refreshSystemSources: () => Promise<void>
   refreshDevices: () => Promise<void>
   refreshBackendSupport: () => Promise<void>
+  selectSystemSource: (sourceId: string | null) => Promise<void>
   selectDevice: (deviceId: string) => Promise<void>
   setCaptureMode: (mode: CaptureMode) => void
   setCapturePolicy: (policy: CaptureBackendPolicy) => Promise<void>
@@ -43,7 +48,9 @@ function applyCaptureStatus(status: CaptureManagerStatus): Partial<AudioState> {
 }
 
 export const useAudioStore = create<AudioState>((set, get) => ({
+  systemSources: [],
   devices: [],
+  selectedSystemSourceId: audioCapture.getSelectedSystemSourceId(),
   selectedDeviceId: null,
   captureMode: 'system',
   capturePolicy: 'auto',
@@ -56,6 +63,21 @@ export const useAudioStore = create<AudioState>((set, get) => ({
   sampleRate: 48000,
   channelCount: 2,
 
+  refreshSystemSources: async () => {
+    const systemSources = await audioCapture.listSources('system')
+    const fallbackSourceId = systemSources[0]?.id ?? null
+    const currentSelectedSystemSourceId = get().selectedSystemSourceId
+    const nextSelectedSystemSourceId = currentSelectedSystemSourceId && systemSources.some((source) => source.id === currentSelectedSystemSourceId)
+      ? currentSelectedSystemSourceId
+      : fallbackSourceId
+
+    audioCapture.setSelectedSystemSourceId(nextSelectedSystemSourceId)
+    set({
+      systemSources,
+      selectedSystemSourceId: nextSelectedSystemSourceId,
+    })
+  },
+
   refreshDevices: async () => {
     const devices = await audioCapture.listDevices()
     set({ devices })
@@ -64,6 +86,16 @@ export const useAudioStore = create<AudioState>((set, get) => ({
   refreshBackendSupport: async () => {
     const backendSupport = await audioCapture.refreshBackendSupport()
     set({ backendSupport })
+    await get().refreshSystemSources()
+  },
+
+  selectSystemSource: async (sourceId: string | null) => {
+    audioCapture.setSelectedSystemSourceId(sourceId)
+    audioCapture.setCaptureMode('system')
+    set({
+      selectedSystemSourceId: audioCapture.getSelectedSystemSourceId(),
+      captureMode: 'system',
+    })
   },
 
   selectDevice: async (deviceId: string) => {
@@ -91,13 +123,15 @@ export const useAudioStore = create<AudioState>((set, get) => ({
   startCapture: async () => {
     set({ captureStatus: 'connecting', captureError: null })
     try {
-      const { captureMode, selectedDeviceId, capturePolicy } = get()
+      const { captureMode, capturePolicy } = get()
       audioCapture.setCaptureMode(captureMode)
       audioCapture.setBackendPolicy(capturePolicy)
       await get().refreshBackendSupport()
 
+      const { selectedDeviceId, selectedSystemSourceId } = get()
+
       if (captureMode === 'system') {
-        await audioCapture.startSystemAudio()
+        await audioCapture.startSystemAudio(selectedSystemSourceId ?? undefined)
       } else {
         await audioCapture.startDevice(selectedDeviceId ?? undefined)
       }

src/types/capture.ts

@@ -13,6 +13,9 @@ export interface CaptureSourceDescriptor {
   id: string
   label: string
   kind: CaptureMode
+  isDefault?: boolean
+  sampleRate?: number
+  channelCount?: number
 }
 
 export interface CaptureBackendSupportEntry {

src/types/nativeCapture.ts

@@ -0,0 +1,47 @@
+export interface NativeMacOSCaptureSupport {
+  available: boolean
+  reason: string | null
+}
+
+export interface NativeMacOSCaptureSource {
+  id: string
+  label: string
+  kind: 'system'
+  isDefault: boolean
+  sampleRate: number
+  channelCount: number
+}
+
+export interface NativeMacOSCaptureStartResult {
+  sampleRate: number
+  channelCount: number
+  deviceId: string
+  deviceLabel: string
+}
+
+export interface NativeMacOSCapturedChunk {
+  left: Float32Array
+  right: Float32Array
+  channelCount: number
+  capturedAtMilliseconds: number
+  sequence: number
+}
+
+export interface NativeMacOSCaptureDrainResult {
+  chunks: NativeMacOSCapturedChunk[]
+  overwriteCount: number
+  queueDepth: number
+}
+
+export interface NativeMacOSCaptureAPI {
+  getSupport: () => NativeMacOSCaptureSupport
+  listOutputDevices: () => NativeMacOSCaptureSource[]
+  start: (deviceId?: string) => NativeMacOSCaptureStartResult
+  stop: () => void
+  drain: (maxChunks?: number) => NativeMacOSCaptureDrainResult
+  nowMilliseconds: () => number
+}
+
+export interface NativeCaptureAPI {
+  macosCapture: NativeMacOSCaptureAPI
+}