Sienna has published a recommended practice proposal RP-NDI-GPI_2019_12 which details a proposal for unambiguous carriage of traditional broadcast GPI information via NDI Metadata connections.

http://www.sienna-tv.com/ndi/gpioverndi.html

This mechanism is already implemented in Sienna's GPI Interface module in the NDI Processing Engine which interfaces with the JLCooper Ebox GPI interface, supporting 24 GPI Inputs and Outputs.

Please feedback any comments to info @ sienna.tv