[BUG]: Preview MIDI 1 loopbacks with Chromium WebMIDI makes browser unresponsive (was Chromium-based browsers ANR)

[Libamidi]

Windows Version

25H2

Service Installation Method

GitHub

SDK version, if appropriate

1.0.17-rc4.25

Location

Other or Unsure (please indicate in additional notes section below)

Type of bug

Performance not as expected

Steps to reproduce

1. Open chromium-based browser (e.g. Edge)
2. Open https://spessasus.github.io/SpessaSynth/
3. Grant MIDI permission
4. Select Settings, disable MIDI input, and change MIDI output to a MIDI 1 loopback
5. Play a MIDI file
6. Browser ANR

Expected behavior

Browser works fine, like a normal application

Additional notes

Firefox doesn't have this issues.

[Psychlist1972]

I have no idea what "ANR" is, but here's what I was able to replicate

Using Edge
Used the demo song "Jump".

• If I use one of the new MIDI 1.0 basic loopbacks, all instances of the browser process go unresponsive.
• If I kill the browser and start fresh, and use one of the MIDI 2.0 loopbacks, the browser remains responsive.

When monitoring the output with the MIDI 1.0 basic loopback, it's very choppy. Not so with the MIDI 2.0 loopback.

Conclusion: something in the MIDI 1 loopback implementation needs fixing. Title changed to reflect this.

Thanks

Pete
Microsoft