I enquired because I do have a Steenbeck 4plate from older times. It isvery heavy. The motor is about the size of a large washing machine motor. The film transport out-feed and take-up relies on the weight of the platens and rolls or film or tape in each to achieve grip of a simple clutch of friction material and a metal disk.
The film transport itself is sprocketed rollers, each side of the “gate”. There is no intermittant movement but a sweeping scan of the passing frame via a multifacetted spinning prism. This introduces a sort of pulsing effect on the image which seems to stretch it slightly in a vertical direction as viewed.
The transport consists of two film paths, one for magnetic film for sound track and one for the image film. Each path is separately clutched to the drive motor which has a 24fps playback, a slower playback and a fast playback/fast-forward function.
Either film path might be adequate for moving film. Because the motor cab be clutched out, the transport could be advanced by another means.
When the screen box is taken off, the image can be projected and on a reflective screen, is adequately bright for video camera to record it. I imagine it might not be too difficult to rig some sort of aerial image arrangement to a compact camera.
This might require some surgery to the deck of the Steenbeck to accommodate the bulk of a video camera, something I am not so keen to do as the Steenbeck I prefer to remain as a viewing machine as well.