mlx-whisper — Local Voice Transcription for Apple Silicon

Enables automatic transcription of voice notes in OpenClaw using Apple's MLX framework. No API key required. Works fully offline. ~60× faster than standard Whisper on M1/M2/M3/M4.

How it works

1. User sends a voice note (Telegram .ogg / WhatsApp .opus)
2. OpenClaw downloads the audio file
3. Passes it to mlx-whisper-transcribe.sh via {{MediaPath}}
4. Transcript is injected as the message body
5. Agent replies to the text content

Setup

Step 1 — Install mlx-whisper

pip3 install mlx-whisper

Verify:

python3 -c "import mlx_whisper; print('OK')"

Step 2 — Install the wrapper script

Find the Python bin path:

python3 -m site --user-base
# e.g. /Users/\x3Cyou>/Library/Python/3.9

Copy bin/mlx-whisper-transcribe.sh from this skill to \x3Cuser-base>/bin/mlx-whisper-transcribe.sh, then make it executable:

PYBIN=$(python3 -m site --user-base)/bin
cp {baseDir}/bin/mlx-whisper-transcribe.sh "$PYBIN/mlx-whisper-transcribe.sh"
chmod +x "$PYBIN/mlx-whisper-transcribe.sh"

Test it:

"$PYBIN/mlx-whisper-transcribe.sh" /path/to/audio.ogg
# First run downloads the model (~465MB). Subsequent runs are instant.

Step 3 — Configure OpenClaw

Add to ~/.openclaw/openclaw.json under tools.media.audio:

{
  "tools": {
    "media": {
      "audio": {
        "enabled": true,
        "models": [
          {
            "type": "cli",
            "command": "\x3Cuser-base>/bin/mlx-whisper-transcribe.sh",
            "args": ["{{MediaPath}}"],
            "timeoutSeconds": 60
          }
        ]
      }
    }
  }
}

Replace \x3Cuser-base> with the output of python3 -m site --user-base.

Step 4 — Restart OpenClaw

openclaw gateway restart

Or restart the OpenClaw app from the menu bar.

Models

The wrapper uses whisper-small-mlx by default (465MB, good balance of speed and accuracy). To change, edit bin/mlx-whisper-transcribe.sh and update path_or_hf_repo:

Language hint (optional)

Pass a language code as the second argument to skip auto-detection (faster):

mlx-whisper-transcribe.sh audio.ogg zh   # Chinese
mlx-whisper-transcribe.sh audio.ogg en   # English

In openclaw.json, add the language to args:

"args": ["{{MediaPath}}", "zh"]

Performance (M3 MacBook Pro, 8GB)

Troubleshooting

• mlx_whisper not found: Run pip3 install mlx-whisper again
• Empty transcript: Audio may be silent or music-only (Whisper transcribes speech only)
• Timeout: Increase timeoutSeconds for long audio files
• Wrong language: Add "language": "zh" or the target language code to args
• Model download fails: Check internet connection; models are cached after first run in ~/.cache/huggingface