Verify local Mumble audio frequency round trip

gumble/gumble/integration_audio_test.go

@@ -58,10 +58,11 @@ func TestLocalMumbleAudioRoundTrip(t *testing.T) {
 	}
 	time.Sleep(500 * time.Millisecond)
 	frame := make([]int16, sendConfig.AudioFrameSize())
-	for i := range frame {
-		frame[i] = int16(12000 * math.Sin(2*math.Pi*440*float64(i)/gumble.AudioSampleRate))
-	}
 	for i := 0; i < 8; i++ {
+		for sample := range frame {
+			index := i*len(frame) + sample
+			frame[sample] = int16(12000 * math.Sin(2*math.Pi*440*float64(index)/gumble.AudioSampleRate))
+		}
 		raw, err := sender.AudioEncoder.Encode(frame, len(frame), sendConfig.AudioDataBytes)
 		if err != nil {
 			t.Fatal(err)
@@ -70,21 +71,45 @@ func TestLocalMumbleAudioRoundTrip(t *testing.T) {
 			t.Fatal(err)
 		}
 	}
+	// Discard the first few decoder warm-up frames before measuring pitch.
+	var packet *gumble.AudioPacket
+	for i := 0; i < 3; i++ {
+		select {
+		case packet = <-listener.packets:
+		case <-time.After(8 * time.Second):
+			t.Fatal("timed out waiting for relayed audio")
+		}
+	}
 	select {
-	case packet := <-listener.packets:
+	case packet = <-listener.packets:
 		peak := 0
-		for _, sample := range packet.AudioBuffer {
-			v := int(sample)
+		crossings := 0
+		previous := 0
+		// The decoder returns interleaved stereo; inspect one channel. A rising
+		// zero-crossing estimate verifies the 440 Hz source survived Opus rather
+		// than merely proving that arbitrary non-silent audio was relayed.
+		for i := 0; i < len(packet.AudioBuffer); i += gumble.AudioChannels {
+			v := int(packet.AudioBuffer[i])
 			if v < 0 {
-				v = -v
-			}
-			if v > peak {
+				if -v > peak {
+					peak = -v
+				}
+			} else if v > peak {
 				peak = v
 			}
+			if previous <= 0 && v > 0 {
+				crossings++
+			}
+			previous = v
 		}
 		if peak < 500 {
 			t.Fatalf("received silent audio peak=%d", peak)
 		}
+		samples := len(packet.AudioBuffer) / gumble.AudioChannels
+		frequency := float64(crossings*gumble.AudioSampleRate) / float64(samples)
+		if math.Abs(frequency-440) > 120 {
+			t.Fatalf("received frequency %.1f Hz, want generated 440 Hz", frequency)
+		}
 	case <-time.After(8 * time.Second):
 		t.Fatal("timed out waiting for relayed audio")
 	}