Function zoom_keyframes 

pub fn zoom_keyframes(
    seg: &ZoomSegment,
    ramp_frames: Frame,
) -> Vec<ZoomKeyframe>

The keyframes of a zoom’s scale curve, for the dopesheet (ED.13): identity at both edges, full amount across the hold, eased between. Four keyframes when there’s a hold; three (a triangle peak) when the ramps fill the window. This is the dopesheet’s view of zoom_at — pass the same ramp_frames.