How to sync video with projectile firing in VR

I have a green screen video of someone throwing a ball every 5 seconds. I then have a spawnpoint to instantiate a ball projectile, but it moves out of sync slowly, presumably because of the fluctuating frame rate of the VR game vs the steady frame rate of the video (25fps). Does anyone have a fix for syncing these events in Unity? I have tried many methods and am now thinking that cinemachine and timeline with an event trigger might work best. But does anyone have any experience with this type of interaction and have a solution that works?

Many thanks

Nick