voice-cat/core/src/audio/apm_processor.cpp

#include "audio/apm_processor.h"

#include <atomic>
#include <chrono>
#include <cmath>

namespace voicecat::audio {

namespace {
int64_t steady_now_ms() {
    return std::chrono::duration_cast<std::chrono::milliseconds>(
               std::chrono::steady_clock::now().time_since_epoch())
        .count();
}
}  // namespace

// ── ApmPassthrough ────────────────────────────────────────────────────────────
// No-op: returns true (VAD always open), does not modify PCM.
// Replaced by WebrtcApmProcessor when VOICECAT_HAS_APM is defined.
class ApmPassthrough final : public ApmProcessor {
   public:
    void process_render(const int16_t*, int, int) override {}
    bool process_capture(int16_t*, int, int) override { return true; }
};

// ── EnergyVadProcessor ──────────────────────────────────────────────────────
// Lightweight, dependency-free energy/RMS VAD — see apm_processor.h's create_vad() doc comment
// for why this exists instead of a real APM. No AEC (process_render is a no-op); doesn't modify
// the PCM it's given, only inspects it.
class EnergyVadProcessor final : public ApmProcessor {
   public:
    EnergyVadProcessor(float rms_threshold, int64_t hang_time_ms)
        : threshold_(rms_threshold), hang_time_ms_(hang_time_ms) {}

    void process_render(const int16_t*, int, int) override {}

    bool process_capture(int16_t* pcm, int samples, int /*sample_rate*/) override {
        if (samples > 0) {
            double sum_sq = 0.0;
            for (int i = 0; i < samples; ++i) {
                double s = static_cast<double>(pcm[i]) / 32768.0;
                sum_sq += s * s;
            }
            double rms = std::sqrt(sum_sq / samples);
            if (rms >= threshold_.load(std::memory_order_relaxed)) last_voice_ms_ = steady_now_ms();
        }
        return (steady_now_ms() - last_voice_ms_) < hang_time_ms_;
    }

    void set_threshold(float t) override {
        threshold_.store(t, std::memory_order_relaxed);
    }

   private:
    std::atomic<float> threshold_;
    int64_t            hang_time_ms_;
    int64_t last_voice_ms_ = 0;  // epoch start -> gate begins closed until first loud frame
};

std::unique_ptr<ApmProcessor> ApmProcessor::create() {
#ifdef VOICECAT_HAS_APM
    // TODO: return std::make_unique<WebrtcApmProcessor>(); — see create_vad()'s doc comment for
    // why this isn't wired up yet (no working Windows/MSVC build upstream).
#endif
    return std::make_unique<ApmPassthrough>();
}

std::unique_ptr<ApmProcessor> ApmProcessor::create_vad(float rms_threshold,
                                                        int64_t hang_time_ms) {
    return std::make_unique<EnergyVadProcessor>(rms_threshold, hang_time_ms);
}

}  // namespace voicecat::audio