This API lets MediaSource apps more effectively customize the HTMLMediaElement.seekable range logic by providing (or removing) a single seekable range that is union'ed with the current buffered ranges to result in a single seekable range which fits both, when media duration is infinite.
Docs: https://www.w3.org/TR/media-source/#dom-mediasource-setliveseekablerange https://www.w3.org/TR/media-source/#dom-mediasource-clearliveseekablerange https://www.w3.org/TR/media-source/#htmlmediaelement-extensions
Samples: https://googlechrome.github.io/samples/media/live-seekable-range.html