I’m working on a mobile-only project with interactive videos which should only display portrait (not landscape) and full screen in any mobile phone device.
In landscape mode it would preferably show a message saying the project is suitable for portrait mode only.
I’m having a hard time figuring out whether I should use fluid boxes and how to use them for this purpose.
I wonder why nobody responds to your question so far. Well, I never had a task like this, so my answer is a hunch. You say interactive video. As far as I know this media type can't be put into a fluid box. I read that somewhere here in this forum.
I would create a New Project / Blank Project ... Then with devices with high physical resolution in mind (like Retina displays) I'd go for a 9:16 size like i.e. 720x1280 pixels. Then place/layout all necessary elements. Make sure that the video is as well in 9:16 ratio format or at least close to that.
Under File / Publish Settings ... I'd check the option: Disallow phone landscape orientation. I guess with this even if the device is turned to Landscape orientation the presentation would stay portrait, hence a user would voluntarily return to portrait orientation.
This is how I would approach this task. But as I've said I haven't tried that myself. No guarantee.
I didn't answer for the same reasons, because I am really tired of having to guess about the terminology. It is perfectly possible that with 'interactive video' is meant a pure interactive course, not what Captivate designates as 'interactive video'. That type of slide video cannot fit in a fluid box, but moreover it seems bit incongruent to have a video in Portrait mode.
That is the reason I didn't answer, but if your crystal ball is correct creating a non-responsive project could be a choice. However: how to cope with all the differen browser sizes in mobile devices? You do suggest a resolution but AFAIK there is no smartphone with that browser resolution. Not all have 16:9 neither.
Alterntive could be a Breakpoint views workflow, using the Position Properties to make sure that the video is always sized up to the width of any browser resolution on the smartphones. This is also possible with Fluid boxes, if you use no flud box, but seems bit weird. Since the most recent version you can have slides where you use no fluid box but only the Position Properties inherited from the older Breakpoint views workflow.