MulticastView v1.0.0

A native macOS app that shows the multicast actually flowing on a network
segment, labelled in the terms an AV operator uses: "sACN universe 12", not
239.255.0.12.

Install

Download MulticastView-v1.0.0.zip below, unzip, and move the app where you like.

The app is unsigned and un-notarised by design — raw packet capture is
impossible in an App Sandbox, and signing for distribution needs a paid Apple
Developer Program membership. A browser download is quarantined, so macOS will
refuse to open it. To open it anyway, either:

• macOS 15 and later — double-click it once and let it be blocked, then go to
  System Settings → Privacy & Security, scroll to the bottom, and click
  Open Anyway. (Apple removed the old Control-click → Open bypass in
  macOS 15; on macOS 13 and 14 that shortcut still works.)

• Any version — clear the quarantine attribute directly:

  xattr -dr com.apple.quarantine /path/to/MulticastView.app

Or skip all of that and
build from source:
a locally built app is never quarantined and simply opens.

Capture privileges

Reading packets needs access to /dev/bpf*, which macOS restricts to the
access_bpf group. Install Wireshark's ChmodBPF helper and log out and back
in. The app detects the problem and explains it rather than just failing.

Requirements

macOS 13 or later. To see past your own port you need a SPAN/mirror port or a
tap — plugged into an ordinary wall port you will see very little, and that is
correct behaviour, not a fault.

Known limits

• Layer-2-only protocols (SoundGrid, CobraNet, AVB/Milan) are invisible: they
  are not IP, and the capture filter accepts IPv4 multicast only.
• The SNMP half has never been exercised against a real agent. Its BER encoding,
  GetBulk walk and PortList decoding are covered by byte-level unit tests only,
  and not every switch exposes multicast forwarding over SNMP at all.
• Interface removal mid-capture is handled in code but untested.

See the README for what
it does and how it is put together.