Making an accessible course relying largely on human v/o and closed captions?

I have made accessible courses with full v/o. On the initial screen, I allow the user to specify their preferences by adding buttons that enable them to toggle the audio and closed captioning on and off.  

Unfortunately , the closed caption feature in Storyline 360 ( I think it is in 3 as well) does not work when you pause or stop the audio so you have to create custom CC if you allow them to turn off the audio. The way I do this is to put the text version for each slide on a layer which will only display if the user enables the cc option on the first slide.

I usually design my slides so that there is some space at the bottom of each slide to display the text without interfering with the content. 

Another thing that I do is if there are special instructions for people using screen readers, I add the text to the slides but make it the same colour as the background. This way the screen reader will pick up the text but other viewers will not see it.

As for not using alt tags on images - my understanding is that people with accessibility issues are entitled to a comparable experience as other users so images should be described. 

As Léonie Watson said: “I used to have sight so I appreciate descriptive alt text on decorative images because it evokes memories of things in my mind.”

Another thing I sometimes do, not always, is play a sound when the nav buttons are  "clicked" with a mouse or tab + enter to signify the action has occurred.

Hope this helps.

Thanks very much for the detailed advice. You're giving me a lot to work with. I have created custom captions before, so that's good to know about the new Storyline CC limitations.

Re alt tags on images: my reluctance to use these tags was because I planned that these screens would already have v/o to present the core content of the course. I was concerned that the screen reader calling out alt tag text at the same time as the v/o was playing would be confusing. (I admittedly am very much a novice with screen readers and I don't know if skilful users can get around this.)

I guess my conflict comes down to these two approaches:

1 - My original plan was for "podcast with pictures and closed captions" where the v/o content would be used by all students with audio capabilities (CC added to match that script exactly). I would add brief display text, images and figures to keep the interest of anyone approaching the course visually, but would "hide" these elements from screen readers to avoid conflict with v/o. Think of something like this: https://youtu.be/oQbei5JGiT8 

If people using screen readers turn off audio in this course design, they will miss most of the course content.

2 - The alternative would be to keep all v/o as a brief intro to each screen, then go silent while using more comprehensive display text and imagery. Alt text and tabbing through text boxes would give those with screen readers the whole experience. But this could be a really text-heavy course, given the scope of the topic.

Thanks again!

if they turn off the audio, i would give them the option to diplay the transcript directly on the slides using the layer idea i mention about. 

You can do this by creating a button that toggles a true/false variable on and off when clicked.  just add a trigger to each slide to show the layer at the start of timeline when variable is true and another trigger to hide the layer if varable is false.

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Good idea! I'll have to just build a prototype and test out my original concept with screen space for everything. I can re-use my existing code which toggled CC on and off. I'm also designing another course with a transcript area at the side so that there's enough room for text without scrolling. Using the built-in Notes tab (labelled Transcript) might also be an option.

I really need to get more practice with NV Access ...

yes, i have used the built-in notes tab for this as well.