Modern video assist is not only about signal reception and distribution, but recording, rough editing, visual effect previz and streaming.
Off-set crew members like producers or clients from remote locations can watch and give notes/directions over video streams.
[2] Director Blake Edwards was the first to use the beam-splitter single-camera system invented by engineer Jim Songer in the 1968 film The Party.
The beam splitter is directly over the ground glass and turns the light again 90 degrees, and projects it onto the chip of the video assist camera—through its own lens system.
On steadicam and remote head or crane operation, the viewfinder and beam splitter is often removed because it's not needed.
HD cameras can output HD-SDI video signals, which, when presented on a high-grade calibrated monitor, is an almost what-you-see-is-what-you-get quality.
The VA software used by the operator keeps a precise log about which take was recorded where, noting the time code or file name.
This is essential for a director to show actors where to change their moves, or to recheck dialogue lines, check shooting angles, correct overlaps, and time camera or stunt actions.
In modern systems, this sync can be done by automated software which takes care of copying the relevant files based on metadata.
The video assist gear often includes an editing software, usually running on the same or a networked machine, so rough cuts can be made by the VA operator right on set.
A portable video mixer, or a similar function built right into the VA software, is useful to check out key, blends or pre-visualize visual effects.
A more complex effect involving motion control or programmable remote heads can see the VA system sending or receiving triggers to such systems, to sync up live and playback images to show the director the effect in real time - for example when the same actor is playing more than one character.