Youtube and Dailymotion clips are able to have external subtitles (closed captions). External means that they are not part of the video frame. So they can be turned off and for one clip may be available several different subtitles.
Note, subtitles are available only in case if the author have uploaded those along with the video. Thus not all videos have subtitles.
On Youtube in addition to regular subtitles are also available two other kinds of subtitles: Automatic Speech Recognition (ASR) and auto-translated subtitles (machine translation of one of regular subtitles or ASR, available only when the clip has some of them).
Filter has options to fine-tune which subtitles to use. They are placed under
Quality Download subtitles options group. Each type of subtitles (regular / ASR / auto-translated) has separate configuration there.
Filter downloads selected subtitles at opening so they will be available at playback. Example:
Names of auto-translated subtitles are appended with "[AT]" string, ASR subtitles - "[ASR]" string. To do not mix all types of subtitles now at first are listed regular subtitles, then ASR, then auto-translated. Within each type they are sorted by language tag (i.e. language code + optional script code or country code).
Help Miscellaneous Subtitles support