The play button is generally what a typical user associates with starting a video so I don't think a mouse over effect will improve your engagement. Mouse effects are also a non-existent aspect for mobile users.
What might help stylistically is the way that the video previews are displayed. Users are used to video previews being in a rectangular shape when they are not within a masonry grid. Making your video previews the full width of the container (with the proportional height) and more rectangular should drive the message much more clearly that these are videos meant to be watched.
Another CSS/js effect you could try is slightly animating the play button on hover. A subtle bounce or a growth animation will tell the user that they are dealing with an interactive element and will encourage them to click on the play button. For example, if you hover over the video preview on this udemy course you will see that the play button grows, encouraging the user to click on it.