commit cd6934049efd095d3597cd0a91378e2ea3b50e05
Author: Alex Savin <alex@savin.nyc>
Date:   Fri Aug 15 11:30:28 2025 -0400

    Add initial implementation of two-tone detector with Docker support

diff --git a/Dockerfile b/Dockerfile
new file mode 100644
index 0000000..bcc0397
--- /dev/null
+++ b/Dockerfile
@@ -0,0 +1,34 @@
+# builder
+FROM golang:alpine AS builder
+
+WORKDIR /app
+ADD . /app
+
+RUN CGO_ENABLED=0 go build -o two-tone-detector
+
+# runner
+FROM alpine:latest
+
+WORKDIR /app
+COPY --from=builder /app/two-tone-detector /app/two-tone-detector
+
+# Metadata params
+ARG VERSION
+ARG BUILD_DATE
+ARG NAME
+ARG VENDOR
+
+# Metadata
+LABEL org.label-schema.build-date=$BUILD_DATE \
+org.label-schema.url="https://alex.savin.nyc" \
+org.label-schema.docker.schema-version="1.0"
+#      org.label-schema.name=$NAME \
+#      org.label-schema.description="Example of multi-stage docker build" \
+#      org.label-schema.vcs-url=https://github.com/alex-savin/$VCS_URL \
+#      org.label-schema.vcs-ref=$VCS_REF \
+#      org.label-schema.vendor=$VENDOR \
+#      org.label-schema.version=$VERSION \
+
+VOLUME /app/config
+
+CMD ["./two-tone-detector"]
diff --git a/go.mod b/go.mod
new file mode 100644
index 0000000..480f141
--- /dev/null
+++ b/go.mod
@@ -0,0 +1,24 @@
+module git.savin.nyc/alex/go-two-tone-detector-file
+
+go 1.25
+
+require (
+	github.com/bluenviron/gortsplib/v4 v4.16.2
+	github.com/go-audio/audio v1.0.0
+	github.com/go-audio/wav v1.1.0
+	github.com/pion/rtp v1.8.21
+)
+
+require (
+	github.com/bluenviron/mediacommon/v2 v2.4.1 // indirect
+	github.com/go-audio/riff v1.0.0 // indirect
+	github.com/google/uuid v1.6.0 // indirect
+	github.com/pion/logging v0.2.4 // indirect
+	github.com/pion/randutil v0.1.0 // indirect
+	github.com/pion/rtcp v1.2.15 // indirect
+	github.com/pion/sdp/v3 v3.0.15 // indirect
+	github.com/pion/srtp/v3 v3.0.7 // indirect
+	github.com/pion/transport/v3 v3.0.7 // indirect
+	golang.org/x/net v0.43.0 // indirect
+	golang.org/x/sys v0.35.0 // indirect
+)
diff --git a/main.go b/main.go
new file mode 100644
index 0000000..42edb07
--- /dev/null
+++ b/main.go
@@ -0,0 +1,479 @@
+package main
+
+import (
+	"flag"
+	"fmt"
+	"log"
+	"log/slog"
+	"math"
+	"os"
+	"os/signal"
+	"sync"
+	"syscall"
+	"time"
+
+	"github.com/bluenviron/gortsplib/v4"
+	"github.com/bluenviron/gortsplib/v4/pkg/base"
+	"github.com/bluenviron/gortsplib/v4/pkg/description"
+	"github.com/bluenviron/gortsplib/v4/pkg/format"
+	"github.com/bluenviron/gortsplib/v4/pkg/url"
+	"github.com/go-audio/audio"
+	"github.com/go-audio/wav"
+	"github.com/pion/rtp"
+)
+
+// Command-line flags
+var (
+	rtspURL       = flag.String("rtsp", "", "RTSP stream URL (e.g., rtsp://localhost:8554/stream)")
+	minAms        = flag.Int("minA", 1000, "Minimum Tone A duration (ms)")
+	minBms        = flag.Int("minB", 3000, "Minimum Tone B duration (ms)")
+	gapMaxMs      = flag.Int("gap", 5000, "Max gap between A and B (ms)")
+	winMs         = flag.Int("win", 100, "Window size (ms)")
+	hopMs         = flag.Int("hop", 50, "Hop size (ms)")
+	ratioThresh   = flag.Float64("ratio", 0.65, "Power ratio threshold for tone detection")
+	rmsThresh     = flag.Float64("rms", 300.0, "Minimum RMS for valid signal")
+	silenceThresh = flag.Float64("silenceThresh", 100.0, "RMS threshold for silence detection")
+	silenceDurMs  = flag.Int("silenceDur", 5000, "Duration of silence (ms) to stop recording")
+)
+
+// decodeMuLaw converts a mu-law encoded byte slice to PCM (int16) samples
+func decodeMuLaw(data []byte) ([]int16, error) {
+	const (
+		bias = 0x84
+		clip = 32635
+	)
+	// Mu-law decoding table (simplified from standard mu-law algorithm)
+	muLawTable := [256]int16{
+		-32124, -31100, -30076, -29052, -28028, -27004, -25980, -24956,
+		-23932, -22908, -21884, -20860, -19836, -18812, -17788, -16764,
+		-15996, -15484, -14972, -14460, -13948, -13436, -12924, -12412,
+		-11900, -11388, -10876, -10364, -9852, -9340, -8828, -8316,
+		-7932, -7676, -7420, -7164, -6908, -6652, -6396, -6140,
+		-5884, -5628, -5372, -5116, -4860, -4604, -4348, -4092,
+		-3900, -3772, -3644, -3516, -3388, -3260, -3132, -3004,
+		-2876, -2748, -2620, -2492, -2364, -2236, -2108, -1980,
+		-1884, -1820, -1756, -1692, -1628, -1564, -1500, -1436,
+		-1372, -1308, -1244, -1180, -1116, -1052, -988, -924,
+		-876, -844, -812, -780, -748, -716, -684, -652,
+		-620, -588, -556, -524, -492, -460, -428, -396,
+		-372, -356, -340, -324, -308, -292, -276, -260,
+		-244, -228, -212, -196, -180, -164, -148, -132,
+		-120, -112, -104, -96, -88, -80, -72, -64,
+		-56, -48, -40, -32, -24, -16, -8, 0,
+		32124, 31100, 30076, 29052, 28028, 27004, 25980, 24956,
+		23932, 22908, 21884, 20860, 19836, 18812, 17788, 16764,
+		15996, 15484, 14972, 14460, 13948, 13436, 12924, 12412,
+		11900, 11388, 10876, 10364, 9852, 9340, 8828, 8316,
+		7932, 7676, 7420, 7164, 6908, 6652, 6396, 6140,
+		5884, 5628, 5372, 5116, 4860, 4604, 4348, 4092,
+		3900, 3772, 3644, 3516, 3388, 3260, 3132, 3004,
+		2876, 2748, 2620, 2492, 2364, 2236, 2108, 1980,
+		1884, 1820, 1756, 1692, 1628, 1564, 1500, 1436,
+		1372, 1308, 1244, 1180, 1116, 1052, 988, 924,
+		876, 844, 812, 780, 748, 716, 684, 652,
+		620, 588, 556, 524, 492, 460, 428, 396,
+		372, 356, 340, 324, 308, 292, 276, 260,
+		244, 228, 212, 196, 180, 164, 148, 132,
+		120, 112, 104, 96, 88, 80, 72, 64,
+		56, 48, 40, 32, 24, 16, 8, 0,
+	}
+
+	pcm := make([]int16, len(data))
+	for i, b := range data {
+		pcm[i] = muLawTable[b]
+	}
+	return pcm, nil
+}
+
+// Goertzel struct for frequency detection
+type goertzel struct {
+	N     int
+	fs    float64
+	k     int
+	coeff float64
+}
+
+func newGoertzel(targetHz float64, fs float64, N int) *goertzel {
+	g := &goertzel{N: N, fs: fs}
+	g.k = int(0.5 + (float64(g.N)*targetHz)/fs)
+	omega := (2.0 * math.Pi * float64(g.k)) / float64(g.N)
+	g.coeff = 2.0 * math.Cos(omega)
+	return g
+}
+
+func (g *goertzel) Power(x []float64) float64 {
+	var s0, s1, s2 float64
+	for i := 0; i < g.N; i++ {
+		s0 = x[i] + g.coeff*s1 - s2
+		s2 = s1
+		s1 = s0
+	}
+	omega := (2.0 * math.Pi * float64(g.k)) / float64(g.N)
+	real := s1 - s2*math.Cos(omega)
+	imag := s2 * math.Sin(omega)
+	return real*real + imag*imag
+}
+
+func windowHann(x []float64) {
+	n := float64(len(x))
+	for i := range x {
+		x[i] *= 0.5 * (1.0 - math.Cos(2.0*math.Pi*float64(i)/(n-1.0)))
+	}
+}
+
+func pcmToFloat(buf []int16, N int) []float64 {
+	out := make([]float64, N)
+	for i := 0; i < N && i < len(buf); i++ {
+		out[i] = float64(buf[i])
+	}
+	return out
+}
+
+func rmsPCM(buf []int16) float64 {
+	var s float64
+	for _, v := range buf {
+		f := float64(v)
+		s += f * f
+	}
+	if len(buf) == 0 {
+		return 0
+	}
+	return math.Sqrt(s / float64(len(buf)))
+}
+
+// twoToneDetector for detecting tone sequences
+type twoToneDetector struct {
+	fs             int
+	winN           int
+	hopN           int
+	ratioThresh    float64
+	rmsThresh      float64
+	minAms         int
+	minBms         int
+	gapMaxMs       int
+	freqs          []float64
+	gzBank         []*goertzel
+	inA            bool
+	aFreq          float64
+	aAccumMs       int
+	aStart         time.Time
+	waitingB       bool
+	bFreq          float64
+	bAccumMs       int
+	bStart         time.Time
+	bEnd           time.Time
+	gapRemainMs    int
+	recording      bool
+	silenceAccumMs int
+	recordBuf      []int16
+}
+
+func newTwoToneDetector(fs, winN, hopN int, ratioThresh, rmsThresh float64, minAms, minBms, gapMaxMs int) *twoToneDetector {
+	freqs := make([]float64, 0)
+	for f := 300.0; f <= 3000.0; f += 10.0 {
+		freqs = append(freqs, f)
+	}
+	gzBank := make([]*goertzel, len(freqs))
+	for i, f := range freqs {
+		gzBank[i] = newGoertzel(f, float64(fs), winN)
+	}
+	return &twoToneDetector{
+		fs:          fs,
+		winN:        winN,
+		hopN:        hopN,
+		ratioThresh: ratioThresh,
+		rmsThresh:   rmsThresh,
+		minAms:      minAms,
+		minBms:      minBms,
+		gapMaxMs:    gapMaxMs,
+		freqs:       freqs,
+		gzBank:      gzBank,
+	}
+}
+
+func (d *twoToneDetector) stepWindow(pcms []int16, t0 time.Time) (event string, aFreq, aDur, bFreq, bDur float64) {
+	xi := pcmToFloat(pcms, d.winN)
+	windowHann(xi)
+
+	var total float64
+	for _, v := range xi {
+		total += v * v
+	}
+
+	r := rmsPCM(pcms)
+	hopDur := time.Millisecond * time.Duration(int(float64(d.hopN)*1000.0/float64(d.fs)))
+	now := t0
+
+	if r < d.rmsThresh {
+		slog.Debug("Window at %s: RMS %.2f below threshold %.2f, resetting", now.Format(time.RFC3339), r, d.rmsThresh)
+		d.reset()
+		return "", 0, 0, 0, 0
+	}
+
+	// Find frequency with highest power
+	bestIdx := -1
+	bestPow := 0.0
+	for i, gz := range d.gzBank {
+		p := gz.Power(xi)
+		if p > bestPow {
+			bestPow = p
+			bestIdx = i
+		}
+	}
+	ratio := bestPow / (total + 1e-12)
+	if ratio < d.ratioThresh {
+		slog.Debug("Window at %s: ratio %.3f below threshold %.3f, resetting", now.Format(time.RFC3339), ratio, d.ratioThresh)
+		d.reset()
+		return "", 0, 0, 0, 0
+	}
+	freq := d.freqs[bestIdx]
+
+	if !d.inA && !d.waitingB && !d.recording {
+		// Looking for Tone A
+		d.inA = true
+		d.aFreq = freq
+		d.aAccumMs = int(hopDur.Milliseconds())
+		d.aStart = now
+	} else if d.inA && !d.waitingB {
+		// Confirming Tone A
+		if math.Abs(freq-d.aFreq) <= 10.0 {
+			d.aAccumMs += int(hopDur.Milliseconds())
+			if d.aAccumMs >= d.minAms {
+				d.inA = false
+				d.waitingB = true
+				d.gapRemainMs = d.gapMaxMs
+			}
+		} else {
+			slog.Debug("Window at %s: freq %.1f Hz differs from Tone A %.1f Hz, resetting", now.Format(time.RFC3339), freq, d.aFreq)
+			d.reset()
+		}
+	} else if d.waitingB {
+		d.gapRemainMs -= int(hopDur.Milliseconds())
+		if d.gapRemainMs <= 0 {
+			slog.Debug("Window at %s: gap exceeded %d ms, resetting", now.Format(time.RFC3339), d.gapMaxMs)
+			d.reset()
+		} else if math.Abs(freq-d.aFreq) > 10.0 {
+			// Check for Tone B
+			if d.bAccumMs == 0 {
+				d.bFreq = freq
+				d.bStart = now
+			} else if math.Abs(freq-d.bFreq) > 10.0 {
+				slog.Debug("Window at %s: freq %.1f Hz differs from Tone B %.1f Hz, resetting B", now.Format(time.RFC3339), freq, d.bFreq)
+				d.bFreq = freq
+				d.bAccumMs = 0
+				d.bStart = now
+			}
+			d.bAccumMs += int(hopDur.Milliseconds())
+			d.bEnd = now.Add(hopDur)
+			if d.bAccumMs >= d.minBms {
+				event = "TWO_TONE_DETECTED"
+				d.recording = true
+				d.silenceAccumMs = 0
+				d.recordBuf = make([]int16, 0)
+				slog.Info("Two-tone detected, starting recording", "at", now.Format(time.RFC3339))
+				return event, d.aFreq, float64(d.aAccumMs), d.bFreq, float64(d.bAccumMs)
+			}
+		}
+	}
+	return "", 0, 0, 0, 0
+}
+
+func (d *twoToneDetector) reset() {
+	d.inA = false
+	d.aFreq = 0
+	d.aAccumMs = 0
+	d.aStart = time.Time{}
+	d.waitingB = false
+	d.bFreq = 0
+	d.bAccumMs = 0
+	d.bStart = time.Time{}
+	d.bEnd = time.Time{}
+	d.gapRemainMs = 0
+}
+
+func saveToWAV(data []int16, sampleRate int) {
+	filename := fmt.Sprintf("dispatch_%d.wav", time.Now().Unix())
+	file, err := os.Create(filename)
+	if err != nil {
+		slog.Error("Error creating WAV file", "error", err)
+		return
+	}
+	defer file.Close()
+
+	enc := wav.NewEncoder(file, sampleRate, 16, 1, 1) // PCM format (AudioFormat=1)
+	intData := make([]int, len(data))
+	for i, v := range data {
+		intData[i] = int(v)
+	}
+	buf := &audio.IntBuffer{
+		Data:           intData,
+		Format:         &audio.Format{SampleRate: sampleRate, NumChannels: 1},
+		SourceBitDepth: 16,
+	}
+	if err := enc.Write(buf); err != nil {
+		slog.Error("Error writing WAV file", "error", err)
+		return
+	}
+	if err := enc.Close(); err != nil {
+		slog.Error("Error closing WAV file", "error", err)
+		return
+	}
+	slog.Info("Saved recording", "fimename", filename, "samples", len(data), "seconds", float64(len(data))/float64(sampleRate))
+}
+
+func main() {
+	logger := slog.New(slog.NewTextHandler(os.Stdout, nil))
+	slog.SetDefault(logger)
+
+	flag.Parse()
+	if *rtspURL == "" {
+		log.Fatal("RTSP URL is required (use -rtsp flag)")
+	}
+
+	const fs = 8000
+	winN := int(float64(fs) * float64(*winMs) / 1000.0)
+	hopN := int(float64(fs) * float64(*hopMs) / 1000.0)
+	if winN <= 0 || hopN <= 0 || hopN > winN {
+		log.Fatalf("Invalid window/hop: winN=%d, hopN=%d", winN, hopN)
+	}
+
+	det := newTwoToneDetector(fs, winN, hopN, *ratioThresh, *rmsThresh, *minAms, *minBms, *gapMaxMs)
+	client := gortsplib.Client{}
+	u, err := url.Parse(*rtspURL)
+	if err != nil {
+		log.Fatalf("Invalid RTSP URL: %v", err)
+	}
+
+	// Convert *url.URL to *base.URL
+	baseURL, err := base.ParseURL(*rtspURL)
+	if err != nil {
+		log.Fatalf("Invalid base URL: %v", err)
+	}
+
+	// Set up signal handling
+	sigChan := make(chan os.Signal, 1)
+	signal.Notify(sigChan, os.Interrupt, syscall.SIGTERM)
+	var wg sync.WaitGroup
+	wg.Add(1)
+
+	// Connect to RTSP stream
+	if err := client.Start(u.Scheme, u.Host); err != nil {
+		log.Fatalf("Failed to connect to RTSP stream: %v", err)
+	}
+	defer client.Close()
+
+	// Find G711 mu-law track
+	session, _, err := client.Describe(u)
+	if err != nil {
+		log.Fatalf("Failed to describe RTSP stream: %v", err)
+	}
+
+	var g711Track *format.G711
+	var selectedMedia *description.Media
+	for _, media := range session.Medias {
+		if g711, ok := media.Formats[0].(*format.G711); ok && g711.MULaw && g711.SampleRate == fs && g711.ChannelCount == 1 {
+			g711Track = g711
+			selectedMedia = media
+			break
+		}
+	}
+	if g711Track == nil || selectedMedia == nil {
+		log.Fatal("No mono 8kHz G711 mu-law track found")
+	}
+
+	// Set up the track
+	_, err = client.Setup(baseURL, selectedMedia, 0, 0)
+	if err != nil {
+		log.Fatalf("Failed to setup RTSP stream: %v", err)
+	}
+
+	// Set up RTP packet handler
+	pcmBuf := make([]int16, 0, 8192)
+	startTime := time.Now()
+	sampleCount := 0
+
+	client.OnPacketRTP(selectedMedia, g711Track, func(pkt *rtp.Packet) {
+		// Decode G711 mu-law to PCM
+		pcm, err := decodeMuLaw(pkt.Payload)
+		if err != nil {
+			slog.Error("Error decoding mu-law", "error", err)
+			return
+		}
+		pcmBuf = append(pcmBuf, pcm...)
+		sampleCount += len(pcm)
+
+		// Process in chunks of ~100ms (800 samples at 8kHz)
+		chunkSize := winN
+		for len(pcmBuf) >= chunkSize {
+			chunk := pcmBuf[:chunkSize]
+			pcmBuf = pcmBuf[chunkSize:]
+			chunkTime := startTime.Add(time.Duration(sampleCount-len(pcmBuf)-chunkSize) * time.Second / time.Duration(fs))
+
+			// Process windows for tone detection
+			for offset := 0; offset <= len(chunk)-winN; offset += hopN {
+				win := chunk[offset:min(offset+winN, len(chunk))]
+				t := chunkTime.Add(time.Duration(offset) * time.Second / time.Duration(fs))
+				event, aFreq, aDur, bFreq, bDur := det.stepWindow(win, t)
+				if event != "" {
+					slog.Info("Detected two-tone sequence:\n")
+					slog.Info("Tone A", "Hz", aFreq, "duration (ms)", aDur)
+					slog.Info("Tone B", "Hz", bFreq, "duration (ms)", bDur)
+					det.reset()
+				}
+			}
+
+			// Recording logic
+			if det.recording {
+				if !det.bEnd.IsZero() && !chunkTime.Before(det.bEnd.Add(100*time.Millisecond)) {
+					r := rmsPCM(chunk)
+					slog.Info("Chunk at %s: RMS=%.2f, silenceThresh=%.2f, silenceAccum=%d ms, recordBuf=%d samples",
+						chunkTime.Format(time.RFC3339), r, *silenceThresh, det.silenceAccumMs, len(det.recordBuf))
+					if r < *silenceThresh {
+						det.silenceAccumMs += int(time.Duration(len(chunk)) * time.Second / time.Duration(fs) / time.Millisecond)
+						if det.silenceAccumMs >= *silenceDurMs && len(det.recordBuf) > 0 {
+							slog.Info("Silence detected, saving recording")
+							saveToWAV(det.recordBuf, fs)
+							det.recording = false
+							det.silenceAccumMs = 0
+							det.recordBuf = nil
+							det.reset()
+						} else {
+							det.recordBuf = append(det.recordBuf, chunk...)
+						}
+					} else {
+						det.silenceAccumMs = 0
+						det.recordBuf = append(det.recordBuf, chunk...)
+					}
+				}
+			}
+		}
+	})
+
+	// Start reading the stream
+	slog.Info("Processing RTSP stream...")
+	if _, err := client.Play(nil); err != nil {
+		log.Fatalf("Failed to play RTSP stream: %v", err)
+	}
+
+	// Wait for signal
+	go func() {
+		<-sigChan
+		slog.Info("Received interrupt, stopping...")
+		if det.recording && len(det.recordBuf) > 0 {
+			slog.Info("Saving final recording")
+			saveToWAV(det.recordBuf, fs)
+		}
+		client.Close()
+		wg.Done()
+	}()
+
+	wg.Wait()
+	slog.Info("Program terminated")
+}
+
+func min(a, b int) int {
+	if a < b {
+		return a
+	}
+	return b
+}