Some video streaming sites use so called - video-in-video trick/technique.
/Two video windows are one-on-another on screen and the upper one is blank/empty/.
The real video is playing on that window, which is below that blank video window.
The Play icon is starting video, (icons are pressed by mouse cursor at the same time).
Now - when the mouse cursor is pressed on another active button - per example on the audio volume
regulator - the video stops (equal with pushing Stop button in video player).
Such kind of tricks. And the real video playing window URL stays unrecognized for watcher -
because - for the start you initiate/start only that upper, blank video window URL.
Such technique is used per example, for subtitles (only) are exposed on upper video window
and video file without subtitles is streaming on video window below.
On screen it looks like you are watching regular .mp4 video with hardcoded subtitles.
When trying to download such video (with subtitles) - the outcome is -
downloaded video is without subtitles.
(because subtitles are playing on another video window, above)
