Sienna has published a recommended practice proposal RP-NDI-DMX_2019_12 which details a proposal for unambiguous carriage of DMX information via NDI Metadata connections.

This mechanism is already implemented in Sienna's ArtnetDMX Interface module in the NDI Processing Engine which interfaces Artnet to DMX devices.
There is also an NDI-DMX send test (along with NDI-MIDI, and NDI-GPI send tests) in the Sienna NDI Signal Generator for macOS.

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