The Safari browser on iOS uses the native Safari video player.
Safari on the desktop also uses its native player when using FairPlay or when the
useNativePlayback flag is enabled.
For displaying webvtt subtitles, Safari on iOS requires the
SUBTITLES attribute in the
EXT-X-STREAM-INF tag of the m3u8 file.
SUBTITLES attribute is optional on browsers such as Chrome and Firefox and when Safari does not use its native video player.
TTML subtitles aren't supported through native Safari. However THEOplayer should be able to handle TTML subtitles on desktop Safari as long as FairPlay is not being used and the
useNativePlayback flag is not enabled.
CEA608 and CEA708 subtitles are supported.
When multiple subtitles with mode
hidden are configured, only one will fire its events such as
cuechange when using Safari's native player.
The following resources provide more information: