Discord: refine voice message handling

docs/channels/discord.md

@@ -393,6 +393,22 @@ Default gate behavior:
 | moderation                                                                                                                                                               | disabled |
 | presence                                                                                                                                                                 | disabled |
 
+## Voice messages
+
+Discord voice messages show a waveform preview and require OGG/Opus audio plus metadata. OpenClaw generates the waveform automatically, but it needs `ffmpeg` and `ffprobe` available on the gateway host to inspect and convert audio files.
+
+Requirements and constraints:
+
+- Provide a **local file path** (URLs are rejected).
+- Omit text content (Discord does not allow text + voice message in the same payload).
+- Any audio format is accepted; OpenClaw converts to OGG/Opus when needed.
+
+Example:
+
+```bash
+message(action="send", channel="discord", target="channel:123", path="/path/to/audio.mp3", asVoice=true)
+```
+
 ## Troubleshooting
 
 <AccordionGroup>