VNC Recorder

Cua sandboxes include a noVNC fork with built-in recording capabilities. This lets you capture human demonstrations as replayable session files for training data collection, evaluation baselines, or debugging.

Recording with the Cua CLI

The easiest way to record demonstrations is with the cua skills command.

1. Start recording

Connect to a sandbox and start recording:

# Record from a Cua Cloud sandbox
cua skills record --sandbox my-sandbox

# Or record from any VNC URL
cua skills record --vnc-url http://localhost:8006/vnc.html

This opens the VNC interface with recording enabled. You'll be prompted for a skill name and description after recording.

2. Perform your demonstration

Interact with the sandbox normally. All mouse and keyboard input is captured along with video.

3. Stop and save

Click Stop Recording in the VNC panel. The CLI processes the recording, generates captions using a VLM, and saves the skill to ~/.cua/skills/<name>/.

4. Replay

View the recorded video:

cua skills replay my-skill

List all saved skills:

cua skills list

Read a skill's prompt:

cua skills read my-skill

Manual Recording

1. Start a sandbox and open the VNC UI

Start a sandbox using Docker or Cua Cloud. The VNC UI will be available at:

• Docker: http://localhost:8006
• Cloud: https://{sandbox-name}.sandbox.cua.ai/vnc.html

2. Enable recording

Add autorecord=1 to the VNC URL to automatically start recording when you connect:

http://localhost:8006/vnc.html?autoconnect=1&autorecord=1

Or click the record button in the control bar before connecting.

3. Perform your demonstration

Interact with the sandbox normally. All VNC traffic (screen updates and input events) is captured.

4. Download the recording

Click Stop Recording, then Download to save the session as a .js file.

5. Replay the recording

Start the playback UI:

# Clone the noVNC fork
git clone https://github.com/trycua/novnc
cd novnc

# Move your recording into the recordings folder
mv ~/Downloads/vnc-recording-*.js ./recordings/

# Start the local server
./utils/novnc_proxy

Then open the playback URL:

http://localhost:6080/tests/vnc_playback.html?data=../recordings/your-recording.js

Streaming to External Server

For automated pipelines, stream recordings directly to a custom server using the record_url parameter. The recording data is streamed as a websockify stream over WebSocket.

Here's a simple recording server:

import asyncio
import websockets

async def handle_recording(websocket):
    with open("recording.bin", "wb") as f:
        async for message in websocket:
            f.write(message)
    print("Recording saved")

async def main():
    async with websockets.serve(handle_recording, "localhost", 6090):
        print("Recording server running on ws://localhost:6090")
        await asyncio.Future()

asyncio.run(main())

Then connect with streaming enabled:

http://localhost:8006/vnc.html?autoconnect=1&autorecord=1&record_url=ws://localhost:6090

Recording data streams to disk in real-time via WebSocket, so the file is ready immediately when the session ends.

URL Parameters

For more details on prompting agents with demonstrations, see Demonstration-Guided Skills.

Reference

For related capabilities, see:

• ShowUI-Aloha - Human-taught GUI agent that learns from demonstrations