When loading a media resource for use by an or element, the TimeRanges interface is used for representing the time ranges of the media resource that have been buffered, the time ranges that have been played, and the time ranges that are seekable.
TimeRanges
MDN Reference
The TimeRanges.length read-only property returns the number of ranges in the object.
TimeRanges.length
The end() method of the TimeRanges interface returns the time offset (in seconds) at which a specified time range ends.
end()
The start() method of the TimeRanges interface returns the time offset (in seconds) at which a specified time range begins.
start()