How does the player on seasonvar.ru/hdrezka.me work?

Question

Software players

Hello!
Need expert advice on how the player is made on seasonvar.ru/hdrezka.me? Interested in the following question:
The player has a choice of different voice acting, subtitles and video quality, how is this done? Separate videos for each choice? Then you get a lot of videos:
1 voice-over - 3 qualities
And for 1 episode there are 3-5 voice-overs, respectively, in the region of 15 different videos for just 1 episode. There isn't enough space.
Or is it done through HLS? But, here the question also arises with the fact that for each episode you need to sit and manually synchronize the tracks with the voice acting and the vidos itself. Too goofy in my opinion.
Please tell me, maybe I'm missing something.