Add device-side E2E audio recording test with Goertzel

Records 1s of 48kHz audio via AAudio input stream and verifies
the captured signal contains a dominant 440Hz tone.

Author: xaionaro@dx.center

tests/e2e/audio-recording-e2e/main.go

@@ -0,0 +1,121 @@
+// E2E test: records audio from AAudio input stream at 48 kHz and verifies
+// the captured signal contains a 440 Hz tone using the Goertzel algorithm.
+//
+// Exit 0 = PASS (440 Hz detected), exit 1 = FAIL.
+package main
+
+import (
+	"fmt"
+	"math"
+	"os"
+	"unsafe"
+
+	"github.com/xaionaro-go/ndk/audio"
+)
+
+// goertzelMagnitude computes the magnitude of a specific frequency in
+// a buffer of int16 PCM samples using the Goertzel algorithm.
+func goertzelMagnitude(samples []int16, targetFreq float64, sampleRate float64) float64 {
+	n := len(samples)
+	k := int(0.5 + float64(n)*targetFreq/sampleRate)
+	w := 2.0 * math.Pi * float64(k) / float64(n)
+	coeff := 2.0 * math.Cos(w)
+
+	var s0, s1, s2 float64
+	for _, sample := range samples {
+		s0 = coeff*s1 - s2 + float64(sample)
+		s2 = s1
+		s1 = s0
+	}
+
+	return s1*s1 + s2*s2 - coeff*s1*s2
+}
+
+func main() {
+	builder, err := audio.NewStreamBuilder()
+	if err != nil {
+		fmt.Fprintf(os.Stderr, "FAIL: create builder: %v\n", err)
+		os.Exit(1)
+	}
+	defer builder.Close()
+
+	builder.
+		SetDirection(audio.Input).
+		SetSampleRate(48000).
+		SetChannelCount(1).
+		SetFormat(audio.PcmI16).
+		SetPerformanceMode(audio.LowLatency).
+		SetSharingMode(audio.Shared)
+
+	stream, err := builder.Open()
+	if err != nil {
+		fmt.Fprintf(os.Stderr, "FAIL: open stream: %v\n", err)
+		os.Exit(1)
+	}
+	defer stream.Close()
+
+	actualRate := float64(stream.SampleRate())
+	fmt.Printf("stream opened: rate=%.0f Hz, channels=%d\n", actualRate, stream.ChannelCount())
+
+	if err := stream.Start(); err != nil {
+		fmt.Fprintf(os.Stderr, "FAIL: start stream: %v\n", err)
+		os.Exit(1)
+	}
+
+	// Read ~1 second of audio.
+	totalFrames := int32(actualRate)
+	buf := make([]int16, 1024)
+	var captured []int16
+
+	for int32(len(captured)) < totalFrames {
+		framesToRead := int32(len(buf))
+		if remaining := totalFrames - int32(len(captured)); remaining < framesToRead {
+			framesToRead = remaining
+		}
+		n, err := stream.Read(unsafe.Pointer(&buf[0]), framesToRead, 1_000_000_000)
+		if err != nil {
+			fmt.Fprintf(os.Stderr, "FAIL: read: %v\n", err)
+			os.Exit(1)
+		}
+		if n == 0 {
+			fmt.Fprintf(os.Stderr, "FAIL: read returned 0 frames\n")
+			os.Exit(1)
+		}
+		captured = append(captured, buf[:n]...)
+	}
+
+	stream.Stop()
+
+	fmt.Printf("captured %d frames\n", len(captured))
+
+	// Goertzel: check 440 Hz vs a few other frequencies.
+	targetFreq := 440.0
+	targetMag := goertzelMagnitude(captured, targetFreq, actualRate)
+
+	// Check energy at non-target frequencies for comparison.
+	otherFreqs := []float64{200, 600, 1000, 2000, 5000}
+	var maxOtherMag float64
+	for _, f := range otherFreqs {
+		mag := goertzelMagnitude(captured, f, actualRate)
+		fmt.Printf("  %.0f Hz magnitude: %.2e\n", f, mag)
+		if mag > maxOtherMag {
+			maxOtherMag = mag
+		}
+	}
+	fmt.Printf("  440 Hz magnitude: %.2e\n", targetMag)
+	fmt.Printf("  max other magnitude: %.2e\n", maxOtherMag)
+
+	// Pass criteria:
+	// 1. 440 Hz energy must be significantly above noise floor.
+	// 2. 440 Hz must be at least 10x stronger than any other checked frequency.
+	if targetMag < 1e10 {
+		fmt.Fprintf(os.Stderr, "FAIL: 440 Hz energy too low (%.2e < 1e10)\n", targetMag)
+		os.Exit(1)
+	}
+	if maxOtherMag > 0 && targetMag/maxOtherMag < 10 {
+		fmt.Fprintf(os.Stderr, "FAIL: 440 Hz not dominant (ratio=%.1f, need >=10)\n", targetMag/maxOtherMag)
+		os.Exit(1)
+	}
+
+	fmt.Println("PASS: 440 Hz tone detected")
+}