Here's the set-up: I'm broadcasting a live video stream in one location, and viewing that stream in a different location on my iPhone using the Facebook app. I'm then using ChromeCast to send the video to my Smart TV, which is running Android. My TV doesn't support Facebook or the Livestream app, so the only way to eliminate the iPhone from the equation is to substitute a laptop computer.
Our streaming provider is Livestream.com (now owned by Vimeo). We are using the Livestream Producer application. We are not using any sort of closed captioning solution. When I watch the video through the Livestream website there are no closed captions and no option to display closed captions.
I have set up our Livestream account to simulcast to Facebook Live, and when I watch one of our videos on Facebook via my computer, there is an option to display captions. Since I'm not sending any captions at the point of origin, and Livestream is not adding captions automatically, my conclusion would be that Facebook is somehow generating captions automatically. All the documentation I've been able to find from Facebook suggests that they don't do this, however, and rely on you to provide captions.
On my iPhone, I've confirmed that closed captioning is turned off in my Accessibility settings, and when I watch a video on my phone, no captions are displayed unless I specifically turn them on. However, when I use ChromeCast to send the video to my Smart TV, there are captions and I can't get rid of them. This is annoying because the captions are delayed. I don't necessarily mind if these captions are available for the hearing impaired, but I don't want to see them on my own Smart TV. I've checked the settings on my TV, and it's not configured to display captions either. I'm not sure what to do beyond putting a cardboard box in front of the bottom-left corner of my TV to hide the captions.