Video quality
there is no quality list shown in settings

your different video sources must be served by data() function like this
videoSource: [
{
src: '..link/to/video-360.mp4',
resolution: '360p',
}, {
src: '..link/to/video-480.mp4',
resolution: '480p',
}, {
src: '..link/to/video-720.mp4',
resolution: '720p',
},
],
if they do it should work.
There is only one video in server uploaded in (720px) with one src.
How can the resolution work.
or back end must work with it to make different resolution for one video or what
or back end must work with it to make different resolution for one video or what -> yes.
This player only gives you the possibility to switch between already existing resolutions, it won't do the transcoding for you.
Either you transcode the different resolutions by yourself and upload them one by one, or you let the server do the transcoding. Possible tool for this is ffmpeg.
Good luck!