Add the countdown in a videdo editing application. It will be a lot faster to do it there.
Are you making one big, long video file of slo-mo clips? Or something else? Please elaborate for better advice.
Why exactly is it more difficult to add a countdown? Do you need a countdown before each individual clip or just at the beginning of all the clips?
I take it that you have 200 video clips now slowed down and rendered to a single movie but you now want to insert a count down at the head of each of these 200 shots.
That's not the way I would have approached the project at all. If there are no cuts inside each of the videos then there's a script that you can get that will look for each cut and slice up the videos into comps.
If each of these 200 videos, which are now one longer video that is rendered, then:
- I hope you rendered to a lossless or nearly lossless codec to so that when you re-render you don't introduce a bunch of compression artifacts and spoil the look of the project.
- I hope you have some kind of easily identifiable mark or consistent time that is going to make it easy to make the 200 cuts necessary to separate the videos into individual pieces.
The fastest way to add and render a countdown or slate to a video is to use a non linear editor like Premiere Pro or Final Cut. Most of the time a slate must contain information about the shot like the name, duration, and other pertinent information. You're going to be putting a fair amount of time into just creating the countdown and slates. Again, I'd do this in a NLE.
Please tell us a little more about your project. Maybe we're misunderstanding what you want to do.