Vito supports attaching WebVTT (or VTT) files to pre-recorded videos. This is a specific format of text file with timestamps that video players can use to display an overlay of captions and/or subtitles for the audio track of your video. These can be toggled on or off by the participant, using the media player controls.
Currently, you need to head to the admin pane to upload a custom thumbnail for a pre-recorded video. Click on the Content tab and choose Videos from the drop-down. Navigate to the relevant video and click Add caption or subtitle:
Enter the language and label (these should match) and upload your VTT file. It will be attached to the video right away, but you may need to republish content in the hub for the captions icon to appear.