Nvidia Highlight is a feature within the Nvidia experience platform allowing unassisted video capturing within many of the newer video game titles available.
A list of customizable features can be found ingame which include killstreaks, deaths and funny moments. Each game is fully supported by Nvidia highlights and caters to what you would expect to want highlighted.
You won't have to wait till the game is over. You can upload your highlight clips direct to Youtube or Facebook ingame in just one click.
Files are limited to 15 second clips though the NVH will continue to capture your highlight over multiple files. Each file is roughly 70mb so your HDD won't be impacted too much.