Thanks for the pointer Tamás! Pulling out VAD from WebRTC worked a treat.
I started with https://github.com/daanzu/py-webrtcvad-wheels and knocked together a hello.cpp and CMakeLists.txt ( https://gist.github.com/p-i-/598da13d2a1a1e2a6ec978e15fa7d892) I have to say, it feels hella awkward that I cannot control the pipeline and use native AudioUnits for this kind of work. Surely it is a mistake on Apple's part to put VAD before AEC, if this is really what they're doing... it's gona trigger VAD callback on incoming/remote audio, rather than user-speech. For a low-power usage scenario (say WatchOS), I really want to be dynamically rerouting -- if there's no audio being sent thru the speaker, I don't want AEC eating CPU cycles, but I DO want VAD detecting user-speech onset. And if audio IS being sent thru the speaker, I want AEC to be subtracting it, and VAD to be operating on this "cleaned" mic-input. I'd love it if VoiceProcessingIO unit took care of all of this. I haven't yet managed to scientifically determine exactly what VoiceProcessingIO unit is actually doing, but if I engage its AEC and VAD and play a sine-wave, it disturbs the VAD callbacks, yet successfully subtracts the sinewave from mic-audio. So I strongly suspect they have these two subcomponents wired up in the wrong order. If this is indeed the case, is there any liklihood of a future fix? Do Apple core-audio devs listen in on this list? π On Thu, 17 Oct 2024 at 10:24, Tamás Zahola via Coreaudio-api < [email protected]> wrote: > You can extract the VAD algorithm from WebRTC by starting at this file: > https://chromium.googlesource.com/external/webrtc/stable/src/+/master/common_audio/vad/vad_core.h > > You'll also need some stuff from the common_audio/signal_processing > folder, but otherwise it's self-contained. > > It's easy for me to get the audio-output-stream for MY app (it just comes > in over the websocket), but I may wish to toggle whether I want my AEC to > be cancelling out any output-audio generated by other processes on my mac. > > > From macOS Ventura onwards it is possible to capture system audio with the > ScreenCaptureKit framework, although your app will need extra privacy > permissions. > > It must be possible on macOS, as apps like soundFlower or blackHole are > able to do it. > > > BlackHole and SoundFlower are using an older technique, where they install > a virtual loopback audio device on the system (you can see it listed in > Audio MIDI Settings as e.g. "BlackHole 2 ch"), and change the system's > default output device to that, then capture from the input port of this > loopback device. But this requires installing the virtual device > in /Library/Audio/Plug-Ins/HAL, which requires admin privileges. > > But mobile, I'm not so sure. My memory of iPhone audio dev (~2008) is that > it was impossible to access this. But there's now some mention of v3 > audio-units being able to process inter-app audio. > > > On iOS you must use the voice-processing I/O unit. Normal apps cannot > capture the system audio output. Technically there is a way to do it with > the ReplayKit framework, but it's a pain in the ass to use, and the primary > purpose of that framework is capturing screen content, not audio. If you > try e.g. Facebook Messenger on iOS, and initiate screen-sharing in a video > call, that's going to use ReplayKit. > > Regards, > Tamás Zahola > > On 17 Oct 2024, at 08:04, π via Coreaudio-api < > [email protected]> wrote: > > Thankyou for the replies. I am glad to see that this mailing-list is still > alive, despite the dwindling traffic this last few years. > > Can I not encapsulate a VPIO unit, and control the input/output > audio-streams by implementing input/render callbacks, or making connections? > > I'm veering towards this approach of manual implementation: Just to use a > (misnamed as it's I/O) HALInput unit on macOS or a RemoteIO unit on the > mobile platforms to access the raw I/O buffers, and write my own pipeline. > > Would it be a good idea to use https://github.com/apple/AudioUnitSDK to > wrap this? My hunch is to minimize the layers/complexity and NOT use this > framework. > > And for the AEC/VAD, can anyone offer a perspective? Arshia? The two > obvious candidates I see are WebRTC and SpeeX. GPT4o reckons WebRTC will be > the most-advanced / best-performant solution, with the downside that it's a > big project (and maybe a more complicated build process), while SpeeX is > more light-weight and will probably do the job well enough for my purposes. > > And as both are open-source, I may have the option of pulling out the > minimal-dependency files and building just those. > > The last question is regarding system-wide audio output. It's easy for me > to get the audio-output-stream for MY app (it just comes in over the > websocket), but I may wish to toggle whether I want my AEC to be cancelling > out any output-audio generated by other processes on my mac. e.g. if I am > watching a YouTube video, maybe I want my AI to listen to that, and maybe I > want it subtracted. So do I have the option to listen to SYSTEM-level audio > output (so as to feed it into my AEC impl)? It must be possible on macOS, > as apps like soundFlower or blackHole are able to do it. But mobile, I'm > not so sure. My memory of iPhone audio dev (~2008) is that it was > impossible to access this. But there's now some mention of v3 audio-units > being able to process inter-app audio. > > π > > On Wed, 16 Oct 2024 at 19:35, Arshia Cont via Coreaudio-api < > [email protected]> wrote: > >> Hi π, >> >> From my experience that’s not possible. VPIO is an option for the lower >> level IO device; so is VAD. You don’t have much control over their >> internals, routing and wirings! Also, from our experience, VPIO has >> different behaviour on different devices. On some iPads we saw “gating” >> instead of actually removing echo (be aware of that!). In the end for a >> similar use-case we ended up doing our own AEC and Activity Detection. >> >> Cheers, >> >> Arshia Cont >> metronautapp.com >> >> >> >> On 15 Oct 2024, at 18:08, π via Coreaudio-api < >> [email protected]> wrote: >> >> Dear Audio Engineers, >> >> I'm writing an app to interact with OpenAI's 'realtime' API >> (bidirectional realtime audio over websocket with AI serverside). >> >> To do this, I need to be careful that the AI-speak doesn't make its way >> out of the speakers, back in thru the mic, and back to their server (else >> it starts to talk to itself, and gets very confused). >> >> So I need AEC, which I've actually got working, >> using kAudioUnitSubType_VoiceProcessingIO >> and AudioUnitSetProperty(kAUVoiceIOProperty_BypassVoiceProcessing, setting >> to False). >> >> Now I also wish to detect when the speaker (me) is speaking or not >> speaking, which I've also managed to do >> via kAudioDevicePropertyVoiceActivityDetectionEnable. >> >> But getting them to play together is another matter, and I'm struggling >> hard here. >> >> I've rigged up a simple test ( >> https://gist.github.com/p-i-/d262e492073d20338e8fcf9273a355b4), where a >> 440Hz sinewave is generated in the render-callback, and mic-input is >> recorded to file in the input-callback. >> >> So the AEC works delightfully, subtracting the sinewave and recording my >> voice. >> And if I turn the sine-wave amplitude down to 0, the VAD correctly >> triggers the speech-started and speech-stopped events. >> >> But if I turn up the sine-wave, it messes up the VAD. >> >> Presumably the VAD is working over the pre-EchoCancelled audio, which is >> most undesirable. >> >> How can I progress here? >> >> My thought was to create an audio pipeline, using AUGraph, but my efforts >> have thus far been unsuccessful, and I lack confidence that I'm even >> pushing in the right direction. >> >> My thought was to have an IO unit that interfaces with the hardware >> (mic/spkr), which plugs into an AEC unit, which plugs into a VAD unit. >> >> But I can't see how to set this up. >> >> On iOS there's a RemoteIO unit to deal with the hardware, but I can't see >> any such unit on macOS. It seems the VoiceProcessing unit wants to do that >> itself. >> >> And then I wonder: Could I make a second VoiceProcessing unit, and have >> vp1_aec split send its bus[1(mic)].outputScope to vp2_vad.bus[1].inputScope? >> >> Can I do this kind of work by routing audio, or do I need to get my hands >> dirty with input/render callbacks? >> >> It feels like I'm going hard against the grain if I am faffing with these >> callbacks. >> >> If there's anyone out there that would care to offer me some guidance >> here, I am most grateful! >> >> π >> >> PS Is it not a serious problem that VAD can't operate on post-AEC input? >> _______________________________________________ >> Do not post admin requests to the list. 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