How do others give clients a preview of your video?

I've got some different workflows now that are more internal at the company I'm at, but when I was freelancing I would use Vimeo to share. It's a lot like YouTube except it's higher quality video. You can share a link but you can also password-protect the video, which can also add another layer of protection against it being shared early. Another recommendation I would have on that is to add a timecode to your reference to help people to know it's not final. Vimeo also has some higher levels that offer more review tools, kind of like what Frame.io offers, but the early stuff I talked about should all be free.

A very common one is to use Frame.io or Wipster. They provide plugins within PrPro, and a 'player' for the client. The client can view the exported H.264 file in the player, and even comment on specific frames.

Neil