New in Adobe Captivate 2019, overlay slides enable you to add a slide to a specific frame along an interactive video’s Timeline. While the video is playing, when it reaches that frame, it pauses, and the slide appears as an overlay.
The video resumes when the overlay ends. It may continue from where it left off or from another bookmarked frame along its Timeline (either back or forward).
Adobe provides an excellent example in the Resources section. It’s called “2019 Release – Interactive Video”.Following a similar technique, I created a short course titled “Are You Ready to Learn?”

In this article, I’ll discuss some of the questions which led me to experiment with overlay slides, and the answers I discovered through testing.

1. Bookmarking Overlay Slides

Question: Can an overlay and a bookmark exist in the same location along the Timeline such that it is possible to jump directly from one overlay to another?
Answer:
Yes.
Initially, I created bookmarks and overlays separately. Then, I accidentally added a bookmark by double-clicking a frame that was already inhabited by an overlay, and “voila!” I had a bookmarked overlay.
I also followed the same process to add overlays to existing bookmarks.

Bookmarks and overlays on the Timeline.

2. Overlay Slide Backgrounds

Question: Are overlays slides required to have a background?
Answer: No.
These images illustrate the effect of overlays slides with and without backgrounds. As you can see, backgrounds create a focal point and can be visually appealing, but they are not essential.

An overlaid slide without a background.

An overlaid slide with a transparent background.

3. Scored Quiz Questions (Not Knowledge Checks)

Question: How can I add scored quiz questions to overlay slides?
Answer: Create custom quiz questions using buttons, smart shapes, and Custom Actions (and possibly JavaScript too).

This image shows custom, scored quiz questions I added to some of the overlay slides. In this situation, the scoring does nothing (because they are acting as knowledge checks), but it is possible.

Quiz reporting.

4. Animation

Question: Do animations work on overlay slides?
Answer: Yes. Perfectly. No problems. No workarounds.
These images show animations on overlay slides.

An animation on an overlay slide.

Animations on an overlay slide.

5. Audio and Closed Captioning

Question: Can audio and closed captioning be added to overlay slides separate from the main video audio?
Answer: Yes.
As you can see from the image, overlay slides can have dedicated audio and closed captions. When the video pauses to display the overlay slide, its audio pauses as well, and its closed caption disappears.

The overlay slide’s audio takes over (very smoothly), as does its closed captions.

Independent audio and closed captions on an overlay slide.

Note: I found it necessary to add a single “space” caption to the point on the main Timeline just before the overlay. Otherwise, when the video resumed, the last caption on the main Timeline flashed briefly before being updated.