- Implemented.

Safari/iPhone recording now uses MP4/AAC when WebM is unavailable.
WebM remains the default when supported and FFmpeg is disabled.
Added optional FFmpeg profiles: recommended M4A/AAC-LC or requested 
MP4/H.264 + AAC.
Added MIME-aware, playsinline audio playback.
Added dashboard controls under Plans & Platform → Voice Transcoding / 
FFmpeg.
Added Apache/Nginx media MIME configuration and documentation.
Core implementation: voice_transcoder.php (line 72), messages.php (line 
86), and cyberchat-app.js (line 635).

README.md

@@ -13,6 +13,7 @@ CyberChat is a framework-free PHP, SQLite, JavaScript, and HTML5 chat applicatio
 - Premium-configurable recording presence for both sending and viewing
 - Premium-configurable automatic voice sending
 - Tier-configurable automatic playback of newly received voice clips
+- Optional FFmpeg voice transcoding to iPhone-compatible AAC/M4A or H.264/AAC MP4
 - Administrator tier overrides that grant plan features without payment
 - Single-worker queued polling with cursor catch-up, request timeouts, deduplication, bounded retry backoff, and a capped browser message buffer
 - Plan-based custom username colors
@@ -29,6 +30,7 @@ CyberChat is a framework-free PHP, SQLite, JavaScript, and HTML5 chat applicatio
 - A web server with HTTPS for production
 - Write access to `db/`, `archive/`, `uploads/voice/`, and `config.json`
 - A modern browser with `MediaRecorder` for voice recording
+- Optional: FFmpeg with AAC support; `libx264` is also required for the H.264 profile
 - Optional: PDO MySQL for the MySQL/MariaDB mirror
 
 ## Installation
@@ -38,7 +40,7 @@ CyberChat is a framework-free PHP, SQLite, JavaScript, and HTML5 chat applicatio
 3. Configure Apache with the included `.htaccess`, or adapt `nginx-example.conf`.
 4. Open `admin.php` and sign in with the initial password `changeme123`.
 5. Immediately change `admin.password` in the Configuration tab.
-6. Open **Plans & Platform** to configure tiers, Mailgun, Stripe, and optional MySQL mirroring.
+6. Open **Plans & Platform** to configure tiers, Mailgun, Stripe, optional voice transcoding, and MySQL mirroring.
 
 The SQLite schema and default Free, Plus, and Pro tiers are created automatically on first use.
 
@@ -115,6 +117,21 @@ Stripe references:
 - <https://docs.stripe.com/api/checkout/sessions/create>
 - <https://docs.stripe.com/webhooks>
 
+## Voice Compatibility and FFmpeg
+
+Browsers that support WebM continue to record WebM by default. Safari and iPhone may record MP4/AAC instead, which the upload API also accepts.
+
+Under **Admin > Plans & Platform > Voice Transcoding / FFmpeg**, configure:
+
+- Enable or disable server-side transcoding
+- FFmpeg executable name or absolute path
+- `M4A / AAC-LC`, recommended for audio-only playback on iPhone, Safari, Android, and desktop
+- `MP4 / H.264 + AAC`, which adds a tiny black H.264 video track for systems requiring a conventional MP4
+- Audio bitrate and conversion timeout
+- Whether to retain the original source when conversion fails
+
+When transcoding is disabled, the original browser recording is stored. WebM remains the preferred default on supported browsers. When enabled, new uploads are converted; existing voice files are unchanged.
+
 ## Archives
 
 The application archives daily messages into:
@@ -143,7 +160,7 @@ Set a PDO MySQL DSN in the dashboard, enable the mirror, and optionally enable a
 <script>
   window.CYBERCHAT_BASE = '/chat';
 </script>
-<script src="/chat/assets/js/cyberchat-app.js?v=20260609.5"></script>
+<script src="/chat/assets/js/cyberchat-app.js?v=20260609.6"></script>
 <script>
   CyberChat.init('#my-chat');
 </script>
@@ -166,6 +183,7 @@ api/stripe-webhook.php       Stripe event synchronization
 assets/js/cyberchat-app.js   Browser application
 lib/mailer.php               Reusable Mailgun sender
 lib/stripe.php               Stripe REST client and subscription sync
+lib/voice_transcoder.php     Optional FFmpeg voice compatibility pipeline
 lib/mysql_mirror.php         Optional SQLite-to-MySQL mirror
 ```