SysEx Not Delivered to RtMidi Virtual Ports on macOS

[shemeshg]

Reference:

• https://stackoverflow.com/questions/21907923/using-rtmidi-midisendsysex-sends-no-events-to-virtual-ports
• SysEx is not propagated shemeshg/MidiRouterClient#9

How to Reproduce

1. Send a SysEx message using
   https://studiocode.dev/webmidi-tester/
   to IAC_Driver.
   Verify in a MIDI monitor that the SysEx message is received correctly.

2. Send the same SysEx message using an RtMidi virtual output port.
   Check the MIDI monitor again — the SysEx message is not received.

Expected Behavior

SysEx messages sent through an RtMidi virtual port on macOS should be received the same way as when using the built‑in IAC_Driver virtual port.

[insolace]

What happens when you send a note-on?The reason I ask is that the virtual ports are tied to the application, they don’t behave like the IAC driver ports. If you send a sysex message to an rtmidi virtual port, it is received inside the application when you read the port with rtmidi, and wont show up in midi monitor. In the application if you write a message to the virtual port, it will show up in midi monitor.On Jan 14, 2026, at 2:59 AM, shemeshg ***@***.***> wrote:shemeshg created an issue (thestk/rtmidi#366) Reference: https://stackoverflow.com/questions/21907923/using-rtmidi-midisendsysex-sends-no-events-to-virtual-ports shemeshg/MidiRouterClient#9 How to Reproduce Send a SysEx message using https://studiocode.dev/webmidi-tester/ to IAC_Driver. Verify in a MIDI monitor that the SysEx message is received correctly. Send the same SysEx message using an RtMidi virtual output port. Check the MIDI monitor again — the SysEx message is not received. Expected Behavior SysEx messages sent through an RtMidi virtual port on macOS should be received the same way as when using the built‑in IAC_Driver virtual port. —Reply to this email directly, view it on GitHub, or unsubscribe.You are receiving this because you are subscribed to this thread.Message ID: ***@***.***>

[shemeshg]

Hi,

I’ve tested this thoroughly. Messages like note on, as well as others such as time and midi sense, are all coming through correctly — so this doesn’t appear to be an application‑level issue.

For testing, I’m using a minimal C++ main that includes RtMidi.h, with a virtual MIDI input and output connected via callback. All “ignore MIDI type” options are set to false.

consider something like

#include <iostream>
#include <vector>
#include "RtMidi.h"

RtMidiOut *midiOut = nullptr;

// Forward everything received on the input to the output
void midiCallback(double timeStamp, std::vector<unsigned char> *message, void *userData)
{
    if (!message || message->empty()) return;

    // Forward to output
    midiOut->sendMessage(message);
}

int main()
{
    try {
        // Create virtual output port
        midiOut = new RtMidiOut();
        midiOut->openVirtualPort("myport");

        // Create virtual input port
        RtMidiIn midiIn;
        midiIn.openVirtualPort("myport");

        // Set ignoreTypes(false, false, false)
        // meaning: do NOT ignore sysex, timing, or sensing messages
        midiIn.ignoreTypes(false, false, false);

        // Set callback
        midiIn.setCallback(&midiCallback);

        std::cout << "Virtual MIDI ports created. Forwarding all messages..." << std::endl;

        // Keep running
        while (true) {
            // Sleep a bit to avoid busy loop
            std::this_thread::sleep_for(std::chrono::milliseconds(100));
        }

    } catch (RtMidiError &error) {
        error.printMessage();
        return 1;
    }

    return 0;
}