First release

This release does not support authentication. A host on this PC accepts connections based on your approval choice, not on a password. Details are in Authentication is not in this release below.

Network MIDI 2.0 carries MIDI over your existing Ethernet or Wi-Fi network, with no MIDI cables and no audio interface in between. A device connected this way appears in Windows like any other MIDI device, so your DAW and other MIDI software can use it straight away.

Windows can work in either direction, and both at once:

• As a client, this PC connects out to a synth, an interface, or another computer.
• As a host, this PC accepts connections from other devices.

To set any of this up, use the Network MIDI 2.0 Setup app. This page does not repeat what that app does; see Network MIDI 2.0 Setup for the walkthrough.

What you need

The two ends must be on the same network and the same subnet. Devices announce themselves locally, and those announcements do not normally cross between separate networks, or between a guest network and your main one.

To accept incoming connections, the service must be allowed through the firewall. This is the single most common reason other devices can see this PC but cannot connect to it: they see the advertisement, and their connection request is dropped before the service ever sees it. See Adding Network MIDI 2 to your firewall.

Connecting out from this PC does not need a firewall change.

Wired is better than Wi-Fi for anything timing-critical. A Wi-Fi radio sleeps between messages, so the first message after a quiet moment waits for it to wake. Most wired networks give round trip times under a millisecond.

Authentication is not in this release

The Network MIDI 2.0 specification defines two optional authentication schemes: a shared password for a host, and a user name and password per user. Neither is supported in this release of Windows MIDI Services. Support is planned as a later update.

What that means in practice:

• A host on this PC cannot be password protected. Control who may connect using the approval policy instead: choose Ask me first so that nothing connects until you allow it, and use Block to refuse a device permanently. This is a real control, and for a home or studio network it is usually the right one.
• This PC cannot connect to a remote device that requires a password. The remote device will ask for authentication and Windows will end the session rather than pretend to authenticate.
• A host asking for authentication will not start at all. If a configuration file names "authentication": "password" or "user", that host is refused at configuration time with AuthenticationNotImplemented. It is deliberately not downgraded to an unprotected host, because silently removing protection somebody asked for would be worse than refusing.

If you need to keep other devices off a host, put it on a network you control, or use Ask me first and approve only the devices you recognize.

How connections behave

Discovery is automatic. Devices that advertise themselves appear on their own, usually within a few seconds. There is nothing to scan.

Connecting can need action at the other end. Many devices will not simply accept an incoming connection; they wait for you to approve it on a web page, a companion app, or a physical button. If a connection sits at “Connecting”, check the device itself. Windows keeps trying, so once you allow it at the other end the connection completes on its own.

Connections are remembered and re-established on their own. A connection you set up survives a restart of the service or the PC, with no app running. If the device is switched off, the entry stays and connects when the device reappears.

A device that does not advertise can be connected by address. Advertised connections are more efficient, because Windows waits for an announcement rather than repeatedly probing an address.

Naming. Leave the name empty and Windows uses whatever the device calls itself. Give a name and that is what appears everywhere in Windows, including your DAW’s device list.

MIDI 1.0 ports are created by default. Alongside the modern UMP endpoint, Windows creates classic MIDI 1.0 ports so that older software, which does not understand the newer combined API, can use the device. Most apps today fall into that category. This applies in both directions: to devices this PC connects out to, and to devices that connect in to a host here. You can turn it off per entry if you only want the UMP endpoint.

Details

The rest of this page is for people who want to understand the transport itself, or who edit the configuration file by hand.

What is implemented

The transport implements the MIDI Association Network MIDI 2.0 (UDP Transport) specification, M2-124-UM version 1.0.

A command the transport does not recognize is answered inside an established session with NAK, reason CommandNotSupported, and is ignored outside one. Commands added to the specification later are therefore refused cleanly rather than half-handled.

Identity on the network

A host is advertised over DNS-SD as _midi2._udp.local.

Datagrams are capped at a 1400 byte UDP payload, which keeps the whole packet inside a standard 1500 byte Ethernet MTU for both IPv4 and IPv6. DontFragment is set, so an oversized datagram is dropped rather than fragmented.

The configuration file

Settings live in C:\ProgramData\Microsoft\MIDI\WindowsMidiServices.midiconfig.json, under the Network MIDI 2.0 transport’s identifier.

The file is designed to be portable: copying it to another PC carries your setup with it.

A few rules apply to the whole file:

• All keys are case-sensitive, including GUIDs.
• GUID keys are written braced and upper case, for example {C95DCD1F-...}.
• Port numbers are written as strings, not numbers.
• A "_comment" key may appear anywhere. It is written by the tools to make the file readable and is never read back by the service.

{
  "endpointTransportPluginSettings": {
    "{C95DCD1F-CDE3-4C2D-913C-528CB8A4CBE6}": {
      "_comment": "Network MIDI 2.0 (UDP)",
      "transportSettings": {
        "maxForwardErrorCorrectionCommandPackets": 2,
        "maxRetransmitBufferCommandPackets": 50,
        "outboundPingInterval": 2000,
        "invitationPendingTimeout": 120000,
        "maxHostConnections": 64,
        "directConnectionScanInterval": 20000
      },
      "create": {
        "hosts": {
          "{8E2F1A44-0C7B-4E5D-9A31-6B0F2D8C1E77}": {
            "name": "Windows MIDI Services Host",
            "serviceInstanceName": "studio-pc",
            "productInstanceId": "3263827-5150Net2Preview",
            "networkProtocol": "udp",
            "port": "auto",
            "allowPortFallback": true,
            "enabled": true,
            "advertise": true,
            "authentication": "none",
            "remoteClientPolicy": "requireApproval",
            "createMidi1Ports": true,
            "fallbackMidi1PortCount": 1,
            "allowedClients": [
              { "umpEndpointName": "Bome BomeBox", "productInstanceId": "kb7C5D0A_1" }
            ],
            "deniedClients": []
          }
        },
        "clients": {
          "{971DA520-4559-4A2F-A72E-F9BEA17521CC}": {
            "networkProtocol": "udp",
            "createMidi1Ports": true,
            "fallbackMidi1PortCount": 1,
            "match": {
              "directHostNameOrIP": "192.168.1.253",
              "directPort": "5004"
            }
          }
        }
      }
    }
  }
}

Transport settings

These apply to the transport as a whole rather than to one host or client.

Two behaviors are worth knowing:

Values are clamped, never refused. A value out of range becomes the nearest bound, and a missing or wrong-typed value becomes the default. A warning is written to the trace when anything was corrected. Read the settings back to see what was actually taken.

Sending a partial transportSettings object resets the keys you left out. Parsing starts from the defaults each time; it is not a merge. Read the current settings, change what you need, and send the whole object back.

Lowering maxHostConnections does not disconnect clients that are already connected.

Host entries

A client identity is { "umpEndpointName": "...", "productInstanceId": "..." }. Identity is used rather than IP address, because a device’s address moves and its identity does not.

Client entries

match carries either an advertised identity or a direct address:

A configured client is in one of four states:

MIDI 1.0 ports

A Network MIDI 2.0 device describes itself with function blocks, which it sends when Windows asks it to during endpoint discovery. Those say how many groups the device uses and in which direction, and Windows creates one MIDI 1.0 source and one destination per group from them. A device that describes itself properly needs nothing configured here.

Not every device answers. Some never complete discovery, and unlike USB there are no group terminal blocks to fall back on, so Windows would have nothing to build ports from. For that case the transport supplies a block of its own, and fallbackMidi1PortCount says how wide it is: the value is the number of source ports and also the number of destination ports. It defaults to 1, because a device which does not describe itself is usually a bridge with a single cable, and 16 would mean 32 ports of clutter in every MIDI 1.0 application.

The fallback is ignored the moment the device does describe itself. Function blocks take precedence, so raising the count for a device that declares three groups changes nothing.

Two things behave differently when you change them:

The difference is not arbitrary. Whether an endpoint has MIDI 1.0 ports at all is settled when the endpoint is built and cannot be changed underneath a running one; how many ports it has is driven by properties the service watches, so that can be rewritten live.

Approval

When a host uses requireApproval, an unknown device is held pending until somebody answers. A decision has a scope:

A device left pending is dropped after invitationPendingTimeout, which defaults to two minutes because it is scaled to somebody walking over to a device rather than to a network round trip.

See also

• Network MIDI 2.0 Setup
• Adding Network MIDI 2 to your firewall
• MidiNetworkTransportManager
• MidiNetworkTransportSettings