There are many ways to display captions with videos in Roku. I am going to show you one popular caption format within one Roku SDK example channel.
Things you will need:
Videoplayer and example from Roku SDK.
Caption Software (if you are doing the captioning, try Subtitle Workshop).
For SRT Captions (Videoplayer Example)
Open showfeed.brs in the source folder of the videoplayer example. Scroll down near the bottom and paste in this code.
Next, open your xml feed and place the <srt> tag after <title>tag. See my example below.
Note:Placing TTML caption files within the srt tag works. I don't know why!
Test playback on Roku for caption display.
Note: Make sure captions are enabled on your device. Go to settings, then captions.