How to cut videos "frame perfect"?

For example “Split At Playhead” function. How can I select exact frame where I want to cut video? Because with a mouse I can select only seconds at best. Same with source windows. I can move current position with shifting pixels, but I can’t select which part of video I want to transfer to Timeline in pixels accuracy. Thank you.

You can only split at frames (video is a string of stills, one still = one frame). Use the scroll keys to advance or rewind a frame at a time.