With HLS adaptive streaming, the video player automatically switches to the bitrate version in accordance with the internet connection of the visitor. The visitor can also select a bitrate version manually via the settings button (the radar icon on the right).  

 

And here an HLS video with .webm fallback, multilingual subtitles and without a poster image. HLS shows the first frame of a video if no poster image is set. The subtitles show automatically here (you can set the behavior of subtitles per video/audio or via default settings):