This is the something-from-nothing, never-seen-before moment-- one of the most exciting but also challenging steps! The translator(s) discuss their understanding of the passages with the exegetical team, and film the very first draft in JSL.
How
Usually it is not done in one shot. Translators might go verse by verse or section by section, and at this point they are just trying to get a fairly coherent portrayal of the passage on video. The team edits together these sections to create an Initial Draft and marks off verses and chapters in the video.
Why
You have to start somewhere! Also, the better the quality of this initial draft, the easier the following revisions will be as they have a good foundation to work from.