Returns an array of objects based on available captions. Information for each object may vary depending on the caption types.
The event is only triggered when captions are present. The list is cleared on each
Sideloaded Captions (VTT, SRT, DFXP)
|id ||The URL of the sideloaded caption file|
|label ||The label that is configured in the player setup.|
|id ||The index of the caption.|
|label ||The label specified within the embedded captions|