Here’s an idea! Let’s make an an HTML <video> play inside the shape of some letters. Like "Knockout Text" except instead of an image behind, it’s video. A live demo will explain more clearly:
See the Pen basic pen by Giulio Mainardi (@mgiulio) on CodePen.
A key objective here is to develop this responsively. The idea is to not only scale the video in size to fit the parent container (as video generally does), but scale the text as well, maintaining the size relationship between the type and underlying video.