Seems to just be a browser-native <video> tag with an overlay that pretty simply controls the quality/time/subtitles. The logic for the controls is at video.js[1] and the logic for the subtitles is at subtitles.js[2] (check the `playSubtitles` function for VTT[3] decoding). All of the sources (the videos for each quality, and the VTT files for each subtitles track) are specified as HTML attributes in vid2.shtml, the linked page.
