This is a paid asset, but now you can download AVPro DeckLink Free.
Detail this asset from Unity Store: Original Link
AVPro DeckLink v1.8.6 (Latest version)
Adds native support for Blackmagic Design’s DeckLink hardware to Unity (currently Windows only).
*DOWNLOAD THE TRIAL VERSION HERE*
Features:
+ *NEW* Unity 2020 support
+ *NEW* Auto bit-depth detection
+ *NEW* DeckLink 8K Pro support
+ Free watermarked trial version available
+ Broadcast standard video input and output
+ Up to 8K video input and output
+ Automatic video input mode detection
+ Multiple inputs supported
+ Low latency output
+ Alpha channel output supported
+ Internal and external keyer supported
+ Audio input and output + IMGUI and uGUI support
+ Material mapping support
+ Easy to use
+ Includes example scenes
+ Include drag and drop components
+ Unity 5.6 and above supported