Blackmagic Mini Converter Sync Generator with power supply. Has holes in case from previous mounting - does not impact operation.
From the manufacturer: The Blackmagic Design CONVMSYNC is a sync generator. This generator will generate a reference signal in either high definition or standard definition parmeters. It is part of the Mini Convertor series and offers six BNC outputs.
Many video standards are supported including, NTSC, PAL, 1080i/59.94, 1080i/50, 1080psf/23.98, 1080psf/24, 720p/59.94 and 720p/50 formats, plus new formats can be added via USB.
