@Tom: Thanks for the feedback! We recently added a "Preload" option for slide background iframes. I have gone ahead and added the same option for our regular iframe element now too.

If you select an iframe in the editor, you'll find this new Preload checkbox in the toolbar. When you insert new iframes the preload setting defaults to your most recent preference.

I'm a new (pro) user, so maybe I've missed something as I'm climbing the learning curve. Do I understand correctly from this thread that iframed slides cannot be preloaded now? This is an important feature for us in our lab -- we do lots of presentations to, err, *impatient* audiences, and have embedded tableau/shiny/etc visualizations that take 20-30 sec to load. Watching the "Loading..." message cycle after a slide transition is not really an option.

Is there a way at this time for me to preload slides, either all at once at the beginning of the presentation or n-slides in advance?

If not, can we get this feature reinstated?

hmmm ... I want just the opposite. I want the preloading back on, or an option to turn it on/off and/or set the number of slides to preload.

I would like an ability to request the loading of an iframe some tunable number of slides before the slide holding the iframe.

The delay loading a YouTube video when showing the fragment that has the iframe of the YouTube video looks amateurish.

We revised this a week ago; iframes now only load for the current slide when it becomes visible, no preloading. Iframes are now also unloaded as soon as the slide is hidden.

Note that this change only applies to the new Slides editor released in September 2014. Decks created prior to that will still preload iframes three slides ahead.

I'd really like this feature to be implemented. I'm teaching a class that uses interactive javascript graphics rendering and when all of my iframes load at once, the whole presentation grinds to a halt. Can you please fix this?

It's a bit better but you still run into a problem if the nearest 3 slides are all loading in iframe content.

This is a good default but granular control of each iframe would be best. When we host our own reveal.js instances we have some simple javascript running in the back ground that allows us to do this.

Thanks for reporting. There has been regression here – we have logic in place for only loading iframes in the nearest three slides but it's stopped working. We'll report back when it's been fixed.