Make a form that will create a bbcode

Hello,

I trying to create a form that will create some sort of bbcode, so I can put it on my phpbb forums. I have no idea how I can explain this, so I'll just use an example in the hope that you can understand what I'm trying to create. 

I use forums quite a lot and I have made a basic bbcode format that I use on a daily basis. It's a bit annoying to post links and titles within the [codes]. I saw someone with a form from Jortform where you could easily fill in some details and Jotform would create a bbcode after you submitted it.

So, for example, I have an [img][/img] tag in my code. I want to create a field where I can just paste the code in and it will create the code like this: [img]youtubeurl[/img]

I hope you understand what I'm trying to create here. I seen people do it, but I can't really figure out how. 

Would you kindly share for instance a link where BBCode has been implemented or how you want it implemented in Jotform and we can see how we can approach it as from the explanation its still not very clear what is to be achieved