Get game audio into the browser via PulseAudio + a WebSocket bridge

VNC/noVNC only ever streams video, so game sound needed a completely
separate path. Adds pulseaudio/pulseaudio-utils/libasound2-plugins and
routes ALSA's default device through Pulse (/etc/asound.conf), so
dosbox/scummvm need zero special config. server.sh starts one
PulseAudio daemon and one pcm_ws_bridge.py (from docker-common) for the
container's whole lifetime, capturing Pulse's single default sink via
parec.

Audio is a single shared mix, not per-game - considered and dropped a
per-slot-isolated design (mirroring the video architecture) as
unnecessary complexity per direction. Every running game's audio just
mixes into the one default sink; every /screen/<name> page connects to
the same AUDIO_PORT.

setup_server.py gains GET /screen/<name> (an iframe onto the game's
noVNC screen plus an Enable Sound button - browsers require a user
gesture before audio can start) and GET /pcm-worklet.js. The "Open
Screen" link simplifies from a client-side-JS-built cross-port link to
a plain same-origin relative link, since /screen/<name> now reads the
real host server-side from the request's own Host header.

Found and fixed a real bug along the way: parec --device=@DEFAULT_SINK@.monitor
looks correct but fails with "Stream error: Invalid argument" - the
actual PulseAudio macro is the single token @DEFAULT_MONITOR@.

Verified end-to-end with real audio, not just plumbing: confirmed via
`pactl list sink-inputs` that dosbox connects to Pulse correctly
(unmuted, uncorked), then used xdotool to advance stuntcar past its
silent title screen and captured real audible game audio (RMS ~9292)
through the WebSocket bridge with a raw Python client.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01NiNnj78HGx1KWyCCo39HSz

scripts/setup_server.py

@@ -28,6 +28,14 @@ Each running game gets its own ephemeral X session (Xvnc + fluxbox +
 websockify on their own display/ports) instead of sharing one screen, so up
 to MAX_CONCURRENT_GAMES can run side by side without fighting over focus or
 being invisible to each other. Starting past that cap is refused.
+
+Audio is deliberately *not* per-game: server.sh starts one PulseAudio daemon
+and one pcm_ws_bridge.py (from docker-common) for the whole container's
+lifetime, capturing PulseAudio's single default sink. Every running game's
+audio mixes together there (normal PulseAudio behavior, no per-game routing
+needed), and every /screen/<name> page connects to that same shared
+AUDIO_PORT - simpler than per-slot audio isolation, at the cost of not being
+able to tell games' audio apart when more than one is running.
 """
 
 import html
@@ -45,10 +53,12 @@ SMB_SHARE = "software"
 SMB_DIR = r"Games\dosbox"
 GAMES_HOME = os.environ["GAMES_HOME"]
 SETUP_PORT = int(os.environ.get("SETUP_PORT", "8080"))
+AUDIO_PORT = int(os.environ.get("AUDIO_PORT", "8081"))
 SCREEN_W = os.environ.get("SCREEN_W", "1024")
 SCREEN_H = os.environ.get("SCREEN_H", "768")
 NOVNC_CERT = "/tmp/novnc.pem"
 NOVNC_KEY = "/tmp/novnc.key"
+SCRIPTS_HOME = os.environ.get("SCRIPTS_HOME", "/opt/scripts")
 
 MAX_CONCURRENT_GAMES = 10
 GAME_DISPLAY_NUMS = list(range(90, 90 + MAX_CONCURRENT_GAMES))  # :90..:99, one per game slot
@@ -274,14 +284,8 @@ def render_page():
         status = pending.get(name)
         screen_html = ""
         if name in novnc_ports:
-            port = novnc_ports[name]
-            link_id = f"novnc-{name}"
             status_html = '<span class="status busy">Running</span>'
-            screen_html = (
-                f'<a id="{link_id}" href="#" target="_blank">Open Screen</a>'
-                f"<script>document.getElementById('{link_id}').href = "
-                f"'https://' + window.location.hostname + ':{port}/';</script>"
-            )
+            screen_html = f'<a href="/screen/{name}" target="_blank">Open Screen</a>'
             actions = button("stop", name, "Stop")
         elif status in ("downloading", "extracting"):
             status_html = f'<span class="status busy">{status}...</span>'
@@ -331,6 +335,38 @@ button {{ padding: 0.3em 0.8em; margin-right: 0.3em; }}
 </html>"""
 
 
+def render_screen_page(name, novnc_port, host):
+    return f"""<!doctype html>
+<html>
+<head>
+<title>{html.escape(name)}</title>
+<style>
+html, body {{ margin: 0; padding: 0; height: 100%; overflow: hidden; }}
+iframe {{ border: none; width: 100%; height: 100%; }}
+#audio-btn {{ position: fixed; top: 1em; right: 1em; z-index: 10; padding: 0.5em 1em; }}
+</style>
+</head>
+<body>
+<button id="audio-btn">Enable Sound</button>
+<iframe src="https://{host}:{novnc_port}/vnc.html?autoconnect=true"></iframe>
+<script>
+document.getElementById('audio-btn').addEventListener('click', async () => {{
+  const btn = document.getElementById('audio-btn');
+  const ctx = new AudioContext({{ sampleRate: 48000 }});
+  await ctx.audioWorklet.addModule('/pcm-worklet.js');
+  const node = new AudioWorkletNode(ctx, 'pcm-worklet-processor', {{ outputChannelCount: [2] }});
+  node.connect(ctx.destination);
+  const ws = new WebSocket('ws://{host}:{AUDIO_PORT}/');
+  ws.binaryType = 'arraybuffer';
+  ws.onmessage = (event) => node.port.postMessage(event.data, [event.data]);
+  btn.disabled = true;
+  btn.textContent = 'Sound enabled';
+}});
+</script>
+</body>
+</html>"""
+
+
 class Handler(BaseHTTPRequestHandler):
     def log_message(self, fmt, *args):
         pass
@@ -343,9 +379,34 @@ class Handler(BaseHTTPRequestHandler):
         self.end_headers()
         self.wfile.write(encoded)
 
+    def _send_file(self, path, content_type):
+        try:
+            with open(path, "rb") as f:
+                content = f.read()
+        except OSError:
+            self._send_html("Not found", status=404)
+            return
+        self.send_response(200)
+        self.send_header("Content-Type", content_type)
+        self.send_header("Content-Length", str(len(content)))
+        self.end_headers()
+        self.wfile.write(content)
+
     def do_GET(self):
-        if urlparse(self.path).path == "/":
+        path = urlparse(self.path).path
+        if path == "/":
             self._send_html(render_page())
+        elif path == "/pcm-worklet.js":
+            self._send_file(os.path.join(SCRIPTS_HOME, "pcm-worklet.js"), "application/javascript")
+        elif path.startswith("/screen/"):
+            name = path[len("/screen/"):]
+            with state_lock:
+                info = running_procs.get(name)
+            if info is None:
+                self._send_html(f"<p>{html.escape(name)} is not running.</p>", status=404)
+                return
+            host = self.headers.get("Host", "localhost").rsplit(":", 1)[0]
+            self._send_html(render_screen_page(name, info["novnc_port"], host))
         else:
             self._send_html("Not found", status=404)