feat(radio): add 2-second pre-buffer to reduce audio lag

Buffer 384 KB of PCM data (~2 seconds at 48kHz stereo) via PassThrough
stream before starting Discord playback. Falls back to immediate start
after 3s timeout for slow streams. Cleanup integrated into stopAudio.

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

server/src/plugins/radio/index.ts

@@ -1,5 +1,6 @@
 import type express from 'express';
 import { spawn, type ChildProcess } from 'node:child_process';
+import { PassThrough } from 'node:stream';
 import {
   joinVoiceChannel, createAudioPlayer, createAudioResource,
   VoiceConnectionStatus, StreamType, getVoiceConnection, entersState,
@@ -37,6 +38,7 @@ interface GuildRadioState {
   channelId: string;
   channelName: string;
   volume: number;
+  prebufferTimeout?: ReturnType<typeof setTimeout>;
 }
 
 interface Favorite {
@@ -75,6 +77,7 @@ function setFavorites(favs: Favorite[]): void {
 function stopAudio(guildId: string): void {
   const state = guildRadioState.get(guildId);
   if (!state) return;
+  if (state.prebufferTimeout) clearTimeout(state.prebufferTimeout);
   try { state.ffmpeg.kill('SIGKILL'); } catch {}
   try { state.player.stop(true); } catch {}
   guildRadioState.delete(guildId);
@@ -168,18 +171,53 @@ async function startStream(
     }
   });
 
+  // ── Pre-buffer: 2 Sekunden PCM puffern bevor Wiedergabe startet ──
+  // 48kHz × 2ch × 2byte = 192.000 B/s → 384 KB ≈ 2s
+  const PRE_BUFFER_BYTES = 384 * 1024;
+  const bufferedStream = new PassThrough({ highWaterMark: PRE_BUFFER_BYTES });
+  let buffered = 0;
+  let prebufferDone = false;
+
+  ffmpeg.stdout!.on('data', (chunk: Buffer) => {
+    bufferedStream.write(chunk);
+    if (!prebufferDone) {
+      buffered += chunk.length;
+      if (buffered >= PRE_BUFFER_BYTES) {
+        prebufferDone = true;
+        startPlayback();
+      }
+    }
+  });
+  ffmpeg.stdout!.on('end', () => bufferedStream.end());
+  ffmpeg.stdout!.on('error', (err) => bufferedStream.destroy(err));
+
   // AudioResource + Player (inlineVolume für Lautstärkeregelung)
   const vol = getVolume(guildId);
-  const resource = createAudioResource(ffmpeg.stdout!, {
+  const resource = createAudioResource(bufferedStream, {
     inputType: StreamType.Raw,
     inlineVolume: true,
   });
   resource.volume?.setVolume(vol);
 
   const player = createAudioPlayer();
-  player.play(resource);
   connection.subscribe(player);
 
+  // Starte Wiedergabe erst wenn Pre-Buffer voll ist (oder nach 3s Timeout)
+  function startPlayback() {
+    if (player.state.status !== 'idle') return; // Already started
+    player.play(resource);
+    console.log(`[Radio] Pre-buffer filled (${Math.round(buffered / 1024)} KB), starting playback`);
+  }
+
+  // Fallback: starte nach 3s auch bei langsamen Streams
+  const prebufferTimeout = setTimeout(() => {
+    if (!prebufferDone) {
+      prebufferDone = true;
+      startPlayback();
+      console.log(`[Radio] Pre-buffer timeout, starting with ${Math.round(buffered / 1024)} KB`);
+    }
+  }, 3000);
+
   player.on('error', (err) => {
     console.error(`[Radio] Player error:`, err.message);
     stopStream(guildId);
@@ -191,7 +229,7 @@ async function startStream(
     stationId, stationName, placeName, country,
     streamUrl, startedAt: new Date().toISOString(),
     ffmpeg, player, resource, channelId: voiceChannelId, channelName,
-    volume: vol,
+    volume: vol, prebufferTimeout,
   });
 
   broadcastState(guildId);