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MIDIDMX is an exporter that sends DMX data directly to VRChat worlds using the VRC-MIDIDMX system. This provides an alternative to video streaming, with lower latency and direct channel control.

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What is VRC-MIDIDMX?

VRC-MIDIDMX is a system created by Micca ([email protected]) that enables DMX control in VRChat worlds via MIDI:
  • Direct DMX control: No video encoding/decoding overhead
  • Low latency: Faster response than streaming
  • 16,384 channels: Supports up to 8 banks of 2,048 channels each
  • Watchdog system: Ensures connection stability
VRC-MIDIDMX must be installed in the VRChat world you want to control. It cannot be added client-side.

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Prerequisites

1

Install loopMIDI

Download and install loopMIDI to create virtual MIDI ports on Windows.
  1. Install loopMIDI
  2. Open loopMIDI
  3. Create a new port (e.g., “loopMIDI Port”)
  4. Keep loopMIDI running
2

Verify VRChat World Support

Ensure the VRChat world you’re using has VRC-MIDIDMX installed and configured. Check with the world creator or documentation.
3

Configure VRChat Audio

In VRChat, set your audio input device to the loopMIDI port:
  1. Open VRChat settings
  2. Go to Audio settings
  3. Set Microphone to “loopMIDI Port” (or your custom port name)

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Configuration

MIDIDMX is added as an exporter in your show configuration.

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Basic Setup

exporters:
  - !MIDIDMX
    midiDevice: loopMIDI Port
    channelsPerUpdate: 100
    idleScanChannels: 10
    useEditorLog: false
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midiDevice
string
default:"loopMIDI Port"
required
The name of the MIDI output device to use. Must match a device name from your system.Set to (none) to disable output.
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channelsPerUpdate
integer
default:"100"
Maximum number of channels to update per frame. Keeps bandwidth usage controlled.
Keep this at 100 or lower until VRChat fixes their buffer limitations. Higher values may cause data loss.
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idleScanChannels
integer
default:"10"
Number of channels to scan during idle periods. Ensures all channels eventually sync even if unchanged.Lower values reduce bandwidth usage but increase time to full sync.
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useEditorLog
boolean
default:"false"
Use Unity Editor log instead of VRChat log for watchdog detection. Only useful during development.

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Adding MIDIDMX in HNode UI

1

Open Exporters Section

In the HNode interface, navigate to the Exporters panel.
2

Add MIDIDMX Exporter

Click the + button and select MIDIDMX from the list of available exporters.
3

Configure MIDI Device

  1. Click in the MIDI Device field
  2. Type the exact name of your loopMIDI port (e.g., “loopMIDI Port”)
  3. Or select from the detected devices list if displayed
4

Adjust Settings (Optional)

  • Leave Channels Per Update at 100 (recommended)
  • Leave Idle Scan Channels at 10 (recommended)
  • Leave Use Editor Log unchecked (unless developing)
5

Reconnect if Needed

If you change the MIDI device or need to reset the connection:Click the Reconnect MIDI Device button in the MIDIDMX settings panel.

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How MIDIDMX Works

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Connection Process

1

Initial Connection

HNode connects to the specified MIDI device and enters ConnectedWait status.
2

World Knocking

HNode sends a sequence of control messages to “knock” on the VRChat world:
  1. KnockStart (CC 127 = 101)
  2. KnockMiddle (CC 127 = 120)
  3. KnockFinish (CC 127 = 107)
The world must respond to establish the connection.
3

Watchdog Monitoring

HNode continuously sends watchdog packets (CC 127 = 127) and monitors the VRChat log file for “MIDIREADY” responses.When detected, status changes to ConnectedSendingData.
4

Data Transmission

DMX data is sent as MIDI note events:
  • Channels 0-1023: Note On events
  • Channels 1024-2047: Note Off events
  • Channel value split into 7-bit MIDI velocity and note number
  • Banks switched via Control Change messages

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Bank System

MIDIDMX supports 8 banks of 2,048 channels each (16,384 total channels):
  • Bank 0: Channels 0-2047 (Universes 0-3)
  • Bank 1: Channels 2048-4095 (Universes 4-7)
  • Bank 2: Channels 4096-6143 (Universes 8-11)
  • Bank 3: Channels 6144-8191 (Universes 12-15)
  • Bank 4: Channels 8192-10239 (Universes 16-19)
  • Bank 5: Channels 10240-12287 (Universes 20-23)
  • Bank 6: Channels 12288-14335 (Universes 24-27)
  • Bank 7: Channels 14336-16383 (Universes 28-31)
Banks are automatically switched when sending channels in different ranges.

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Status Indicators

MIDIDMX provides three connection states:

Disconnected

No MIDI device connection. Check device name and loopMIDI.

ConnectedWait

Connected to MIDI, waiting for VRChat world to respond. Make sure you’re in a world with VRC-MIDIDMX.

ConnectedSendingData

Actively sending data to VRChat. Lights should respond to DMX input.

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Troubleshooting

  • Verify loopMIDI is running
  • Check the MIDI device name exactly matches your loopMIDI port
  • Click “Reconnect MIDI Device” in HNode
  • Try restarting loopMIDI
  • Ensure no other application is using the MIDI port
  • Verify you’re in a VRChat world with VRC-MIDIDMX installed
  • Check VRChat’s audio input is set to the loopMIDI port
  • Ensure VRChat is actually running (not just the loader)
  • Look for “MIDIREADY” in the VRChat log file:
    • Location: %AppData%\..\LocalLow\VRChat\VRChat\output_log_*.txt
  • Try leaving and rejoining the world
  • Verify status is ConnectedSendingData
  • Ensure ArtNet is being sent to HNode (check HNode statistics)
  • Verify the world’s gridnode configuration matches your serializer
  • Check that fixture addresses in your lighting console match the world’s setup
  • Try sending a simple static value generator to test: 
    generators:
  - !GeneratorStaticValue
    startChannel: 0
    endChannel: 50
    value: 255
  • Lower channelsPerUpdate (try 50 or 75)
  • Increase idleScanChannels slightly (try 20)
  • Check VRChat performance (low FPS affects MIDIDMX reception)
  • Ensure HNode is running at target framerate (check statistics)
  • Close other applications using the MIDI port
The watchdog system should maintain connection, but if it drops:
  • Check VRChat didn’t crash or reload
  • Verify loopMIDI is still running
  • Look for errors in the VRChat log
  • Try increasing the watchdog timeout (requires code modification)
The log file location:
C:\Users\YourName\AppData\LocalLow\VRChat\VRChat\output_log_*.txt
  • Multiple log files may exist; HNode uses the most recent
  • If using Unity Editor for world development, enable useEditorLog: true

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Performance Optimization

Limit Channel Updates

Keep channelsPerUpdate at 100 or lower. Higher values may overwhelm VRChat’s buffers.

Optimize Idle Scanning

Lower idleScanChannels (5-10) reduces bandwidth but increases sync time. Balance based on your needs.

Use Appropriate Universes

Only use the banks/universes you need. Unnecessary channels still consume update bandwidth.

Match Framerate

Set HNode’s targetFramerate to match your lighting console’s output rate (typically 30-40 FPS).

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Combining MIDIDMX with Streaming

You can use MIDIDMX alongside video streaming for redundancy or different purposes: 
exporters:
  - !MIDIDMX
    midiDevice: loopMIDI Port
    channelsPerUpdate: 100

# Still output via Spout for OBS streaming
spoutOutputName: HNode Output
serializer: !VRSL
This allows:
  • Direct DMX control via MIDIDMX (low latency)
  • Video visualization via streaming (for viewers)
  • Fallback if one system fails

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Advanced: Editor Development Mode

When developing VRC-MIDIDMX worlds in Unity Editor: 
exporters:
  - !MIDIDMX
    midiDevice: loopMIDI Port
    useEditorLog: true
This reads from the Unity Editor log instead of VRChat’s log file, enabling testing without launching VRChat.

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Next Steps

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