Add microphone gain control with live slider on dashboard

- Software gain applied per chunk in audio_ws via struct pack/unpack (S16_LE, clamped)
- Default gain 2.0 (200%) – compensates for quiet USB mics
- GET/POST /api/audio-gain to read and persist gain to /var/lib/babycam/audio-gain
- index.html: Mikrofon-Lautstärke slider card (0–500%), updates live with 300ms debounce
- Gain survives service restarts (loaded from file at startup)

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

app/main.py

@@ -10,6 +10,7 @@ import subprocess
 import re
 import time
 import os
+import struct
 import threading
 from flask import Flask, Response, render_template, request, jsonify
 from flask_sock import Sock
@@ -114,6 +115,30 @@ def stream():
 AUDIO_SAMPLERATE = 16000
 AUDIO_CHUNK = 512  # ~32ms bei 16kHz
 
+GAIN_FILE = "/var/lib/babycam/audio-gain"
+_audio_gain: float = 2.0  # Default 200 % – USB-Mics sind oft leise
+
+
+def _load_audio_gain():
+    global _audio_gain
+    try:
+        with open(GAIN_FILE) as f:
+            _audio_gain = max(0.0, min(10.0, float(f.read().strip())))
+    except Exception:
+        pass
+
+
+_load_audio_gain()
+
+
+def _apply_gain(chunk: bytes, gain: float) -> bytes:
+    """Verstärkt 16-bit PCM LE in-place (clamped)."""
+    if abs(gain - 1.0) < 0.005:
+        return chunk
+    n = len(chunk) // 2
+    samples = struct.unpack(f"<{n}h", chunk)
+    return struct.pack(f"<{n}h", *(max(-32768, min(32767, int(s * gain))) for s in samples))
+
 
 def find_audio_device() -> str:
     """Findet die USB-Soundkarte dynamisch anhand des Namens."""
@@ -148,7 +173,7 @@ def audio_ws(ws):
             chunk = process.stdout.read(AUDIO_CHUNK)
             if not chunk:
                 break
-            ws.send(chunk)
+            ws.send(_apply_gain(chunk, _audio_gain))
     except Exception:
         pass
     finally:
@@ -300,6 +325,27 @@ def wifi_connect():
     })
 
 
+# ---------------------------------------------------------------------------
+# Audio-Gain API
+# ---------------------------------------------------------------------------
+
+@app.route("/api/audio-gain", methods=["GET"])
+def api_audio_gain_get():
+    return jsonify({"gain": _audio_gain})
+
+
+@app.route("/api/audio-gain", methods=["POST"])
+def api_audio_gain_set():
+    global _audio_gain
+    data = request.get_json()
+    value = max(0.0, min(10.0, float(data.get("gain", 1.0))))
+    _audio_gain = value
+    os.makedirs(os.path.dirname(GAIN_FILE), exist_ok=True)
+    with open(GAIN_FILE, "w") as f:
+        f.write(str(value))
+    return jsonify({"success": True, "gain": _audio_gain})
+
+
 # ---------------------------------------------------------------------------
 # System
 # ---------------------------------------------------------------------------

app/templates/index.html

@@ -237,6 +237,14 @@
       <label>Laufzeit</label>
       <div class="value">{{ status.uptime }}</div>
     </div>
+    <div class="card">
+      <label>Mikrofon-Lautstärke</label>
+      <div style="display:flex;align-items:center;gap:.75rem;margin-top:.5rem;">
+        <input type="range" id="gain-slider" min="0" max="500" step="10" value="200"
+               style="flex:1;accent-color:#1976d2;cursor:pointer;">
+        <span id="gain-label" style="font-size:.95rem;font-weight:500;min-width:3.5rem;text-align:right;">200%</span>
+      </div>
+    </div>
     <div class="card">
       <label>System</label>
       <div style="display:flex;gap:.4rem;margin-top:.3rem;flex-wrap:wrap;">
@@ -264,6 +272,31 @@
 </div>
 
 <script>
+  // Mikrofon-Gain
+  (async () => {
+    try {
+      const res = await fetch("/api/audio-gain");
+      const { gain } = await res.json();
+      const pct = Math.round(gain * 100);
+      document.getElementById("gain-slider").value = pct;
+      document.getElementById("gain-label").textContent = pct + "%";
+    } catch (e) {}
+  })();
+
+  let gainTimer;
+  document.getElementById("gain-slider").addEventListener("input", function () {
+    const pct = parseInt(this.value);
+    document.getElementById("gain-label").textContent = pct + "%";
+    clearTimeout(gainTimer);
+    gainTimer = setTimeout(() => {
+      fetch("/api/audio-gain", {
+        method: "POST",
+        headers: { "Content-Type": "application/json" },
+        body: JSON.stringify({ gain: pct / 100 }),
+      });
+    }, 300);
+  });
+
   let selectedSSID = null;
 
   async function scanNetworks() {