diff --git a/package.json b/package.json
index 3b2cf15..03d1c5a 100644
--- a/package.json
+++ b/package.json
@@ -8,6 +8,8 @@
   "scripts": {
     "start": "node src/server/index.js",
     "dev": "nodemon src/server/index.js",
+  "audio:convert": "node scripts/convert-to-opus.js",
+  "audio:convert:dry": "node scripts/convert-to-opus.js --dry-run",
     "years:resolve": "node scripts/resolve-years.js",
     "years:resolve:10": "node scripts/resolve-years.js --max 10",
     "years:force": "node scripts/resolve-years.js --force",
@@ -27,6 +29,7 @@
   },
   "devDependencies": {
     "@eslint/js": "^9.11.1",
+  "ffmpeg-static": "^5.2.0",
     "eslint": "^9.11.1",
     "eslint-config-prettier": "^9.1.0",
     "eslint-plugin-import": "^2.29.1",
diff --git a/scripts/convert-to-opus.js b/scripts/convert-to-opus.js
new file mode 100644
index 0000000..15bb6ed
--- /dev/null
+++ b/scripts/convert-to-opus.js
@@ -0,0 +1,162 @@
+#!/usr/bin/env node
+// Batch convert audio files in data/ to Opus using ffmpeg
+// Usage: node scripts/convert-to-opus.js [--force] [--dry-run] [--bitrate 96] [--concurrency 2]
+// Requires: ffmpeg in PATH or dev dependency ffmpeg-static
+
+import fs from 'fs';
+import path from 'path';
+import { fileURLToPath } from 'url';
+import { spawn } from 'child_process';
+import { createRequire } from 'module';
+
+const __filename = fileURLToPath(import.meta.url);
+const __dirname = path.dirname(__filename);
+const ROOT = path.resolve(__dirname, '..');
+const DATA_DIR = path.resolve(ROOT, 'data');
+
+function parseArgs(argv) {
+  const args = { force: false, dryRun: false, bitrate: 96, concurrency: 2 };
+  const skip = new Set();
+  for (let i = 2; i < argv.length; i++) {
+    if (skip.has(i)) continue;
+    const a = argv[i];
+    if (a === '--force' || a === '-f') args.force = true;
+    else if (a === '--dry-run' || a === '-n') args.dryRun = true;
+    else if (a === '--bitrate' || a === '-b') {
+      const next = argv[i + 1];
+      const v = Number(next);
+      if (!Number.isFinite(v) || v <= 0) throw new Error('Invalid --bitrate');
+      args.bitrate = v;
+      skip.add(i + 1);
+    } else if (a === '--concurrency' || a === '-j') {
+      const next = argv[i + 1];
+      const v = Number(next);
+      if (!Number.isFinite(v) || v <= 0) throw new Error('Invalid --concurrency');
+      args.concurrency = Math.max(1, Math.floor(v));
+      skip.add(i + 1);
+    } else {
+      throw new Error(`Unknown arg: ${a}`);
+    }
+  }
+  return args;
+}
+
+function ensureDataDir() {
+  if (!fs.existsSync(DATA_DIR)) {
+    throw new Error(`Data directory not found: ${DATA_DIR}`);
+  }
+}
+
+function listSources() {
+  const exts = ['.mp3', '.wav', '.m4a', '.ogg'];
+  return fs
+    .readdirSync(DATA_DIR)
+    .filter((f) => exts.includes(path.extname(f).toLowerCase()))
+    .map((f) => ({ src: path.join(DATA_DIR, f), base: f }));
+}
+
+function opusPathFor(base) {
+  const name = base.replace(/\.[^.]+$/i, '.opus');
+  return path.join(DATA_DIR, name);
+}
+
+function findFfmpeg() {
+  // Prefer local ffmpeg-static if present
+  try {
+    const require = createRequire(import.meta.url);
+    const ff = require('ffmpeg-static');
+    if (ff) return ff;
+  } catch {}
+  return 'ffmpeg';
+}
+
+function convertOne({ src, dst, bitrate, dryRun }) {
+  return new Promise((resolve) => {
+    const args = [
+      '-y',
+      '-i',
+      src,
+      '-vn',
+      '-c:a',
+      'libopus',
+      '-b:a',
+      `${bitrate}k`,
+      '-application',
+      'audio',
+      dst,
+    ];
+
+    if (dryRun) {
+      return resolve({ ok: true, skipped: true, reason: 'dry-run', src, dst });
+    }
+
+    const ffmpegBin = findFfmpeg();
+    const child = spawn(ffmpegBin, args, { stdio: ['ignore', 'pipe', 'pipe'] });
+    let stdout = '';
+    let stderr = '';
+    child.stdout.on('data', (d) => (stdout += d.toString()));
+    child.stderr.on('data', (d) => (stderr += d.toString()));
+    child.on('error', (err) => resolve({ ok: false, src, dst, error: String(err) }));
+    child.on('close', (code) => {
+      if (code === 0) resolve({ ok: true, src, dst, stdout, stderr });
+      else resolve({ ok: false, src, dst, code, stdout, stderr });
+    });
+  });
+}
+
+async function run() {
+  try {
+    const { force, dryRun, bitrate, concurrency } = parseArgs(process.argv);
+    ensureDataDir();
+    const sources = listSources();
+    if (sources.length === 0) {
+      console.log('No source files found in data/.');
+      return;
+    }
+    const jobs = sources.map((s) => {
+      const dst = opusPathFor(s.base);
+      const exists = fs.existsSync(dst);
+      const skip = exists && !force;
+      return { ...s, dst, skip };
+    });
+
+    const toDo = jobs.filter((j) => !j.skip);
+    const skipped = jobs.filter((j) => j.skip);
+    if (skipped.length)
+      console.log(`Skipping ${skipped.length} existing .opus files (use --force to overwrite)`);
+    console.log(
+      `Converting ${toDo.length} file(s) to Opus @ ${bitrate} kbps with concurrency ${concurrency}...`
+    );
+
+    let ok = 0;
+    let fail = 0;
+    const queue = [...toDo];
+    const workers = new Array(Math.min(concurrency, queue.length)).fill(null).map(async () => {
+      while (queue.length) {
+        const job = queue.shift();
+        const res = await convertOne({ src: job.src, dst: job.dst, bitrate, dryRun });
+        if (res.ok) {
+          ok++;
+          console.log(
+            `✔ ${path.basename(job.src)} -> ${path.basename(job.dst)}${dryRun ? ' [dry-run]' : ''}`
+          );
+        } else {
+          fail++;
+          console.error(
+            `✖ Failed: ${path.basename(job.src)} -> ${path.basename(job.dst)} (${res.code ?? res.error ?? 'error'})`
+          );
+        }
+      }
+    });
+
+    await Promise.all(workers);
+    console.log(
+      `Done. Success: ${ok}, Failed: ${fail}, Skipped: ${skipped.length}${dryRun ? ' (dry-run)' : ''}`
+    );
+  } catch (e) {
+    console.error('Error:', e.message);
+    process.exitCode = 1;
+  }
+}
+
+run();
diff --git a/src/server/routes/audio.js b/src/server/routes/audio.js
index a8df76e..c1ce7e7 100644
--- a/src/server/routes/audio.js
+++ b/src/server/routes/audio.js
@@ -1,12 +1,23 @@
+import path from 'path';
 import { TOKEN_TTL_MS_DEFAULT, putToken, getToken } from './audio/tokenStore.js';
 import { resolveSafePath, fileExists, statFile, getMimeType } from './audio/pathUtils.js';
 import { headFile, streamFile } from './audio/streaming.js';
 import { getCoverForFile } from './audio/coverService.js';
 
 export function createAudioToken(name, ttlMs = TOKEN_TTL_MS_DEFAULT) {
-  const resolved = resolveSafePath(name);
+  let resolved = resolveSafePath(name);
   if (!resolved) throw new Error('Invalid path');
   if (!fileExists(resolved)) throw new Error('Not found');
+
+  // Prefer .opus sibling for streaming, to save bandwidth
+  const ext = path.extname(resolved).toLowerCase();
+  if (ext !== '.opus') {
+    const opusCandidate = resolved.slice(0, -ext.length) + '.opus';
+    if (fileExists(opusCandidate)) {
+      resolved = opusCandidate;
+    }
+  }
+
   const stat = statFile(resolved);
   const type = getMimeType(resolved, 'audio/mpeg');
   return putToken({ path: resolved, mime: type, size: stat.size }, ttlMs);
diff --git a/src/server/routes/audio/pathUtils.js b/src/server/routes/audio/pathUtils.js
index ce59db4..a44c6c4 100644
--- a/src/server/routes/audio/pathUtils.js
+++ b/src/server/routes/audio/pathUtils.js
@@ -29,5 +29,8 @@ export function statFile(p) {
 }
 
 export function getMimeType(p, fallback = 'audio/mpeg') {
-  return mime.getType(p) || fallback;
+  const t = mime.getType(p) || fallback;
+  // Some clients expect audio/ogg for .opus in Ogg container
+  if (/\.opus$/i.test(p)) return 'audio/ogg';
+  return t;
 }
diff --git a/src/server/tracks.js b/src/server/tracks.js
index 54bd46b..07847e6 100644
--- a/src/server/tracks.js
+++ b/src/server/tracks.js
@@ -6,10 +6,23 @@ import { loadYearsIndex } from './years.js';
 
 export async function listTracks() {
   const years = loadYearsIndex();
-  const files = fs.readdirSync(DATA_DIR).filter((f) => /\.(mp3|wav|m4a|ogg)$/i.test(f));
+  const files = fs
+    .readdirSync(DATA_DIR)
+    .filter((f) => /\.(mp3|wav|m4a|ogg|opus)$/i.test(f))
+    .filter((f) => {
+      // If both base.ext and base.opus exist, list only once (prefer .opus)
+      const ext = path.extname(f).toLowerCase();
+      if (ext === '.opus') return true;
+      const opusTwin = f.replace(/\.[^.]+$/i, '.opus');
+      return !fs.existsSync(path.join(DATA_DIR, opusTwin));
+    });
   const tracks = await Promise.all(
     files.map(async (f) => {
-      const fp = path.join(DATA_DIR, f);
+      // Prefer .opus for playback if exists
+      const ext = path.extname(f).toLowerCase();
+      const opusName = ext === '.opus' ? f : f.replace(/\.[^.]+$/i, '.opus');
+      const chosen = fs.existsSync(path.join(DATA_DIR, opusName)) ? opusName : f;
+      const fp = path.join(DATA_DIR, chosen);
       let year = null;
       let title = path.parse(f).name;
       let artist = '';
@@ -19,8 +32,8 @@ export async function listTracks() {
         artist = meta.common.artist || artist;
         year = meta.common.year || null;
       } catch {}
-      const y = years[f]?.year ?? year;
-      return { id: f, file: f, title, artist, year: y };
+      const y = years[f]?.year ?? years[chosen]?.year ?? year;
+      return { id: chosen, file: chosen, title, artist, year: y };
     })
   );
   return tracks;