Feature: Add pipeline that generates 'video "seam" previews'

[paulhchoi]

Is your feature request related to a problem? Please describe.

There are times when we run the full video generation process, only to find that the "seam" from the end of the intro clip (where donny says 'thank you for watching', etc) to the start of the main clip (generally the scripture reader walking up to the stage) is either mistimed, because the timestamps we added were wrong, or "frozen"/"stuck"/"glitchy" etc etc etc, for a second or so.

Describe the solution you'd like

Creating something like make preview or something, where the processor generates and outputs two clips:

1. a clip of just the last 5 seconds of the intro, merged with the first 5 seconds of the main video
2. a clip of just the last 5 seconds of the main, merged with the first 5 seconds of the outro video
   This way the user running the processor can get a quick 'preview' of the "seam" that they've chosen, where they can validate that the timestamp was correct and that that seam doesn't have any glitches.