When a MIDI output connection is closed on Windows, this results in a call to midiOutReset. This sends "all notes off" and "reset all controllers" MIDI commands to every MIDI channel, 32 commands in all.

For the application I'm working on, this is at least unnecessary, and possibly harmful, depending on my hardware setup. The app targets a controller, only, and this activity could have undesirable side-effects on other devices. It also seems somewhat out of keeping with midir's low-level target functionality.

However, the documentation for midiOutReset also specifies that it stops processing of pending output buffers. midiOutClose will return an error if output is still pending (MIDIERR_STILLPLAYING). I wonder if that's why the call to midiOutReset exists. It might be better to retry midiOutClose until that error no longer occurs (similar to what happens on a call to midiOutUnprepareHeader on a send).

If there's interest in such a change I could try it out, and produce a pull request.

https://learn.microsoft.com/en-us/windows/win32/api/mmeapi/nf-mmeapi-midioutreset