[linux] No option to use external player.

[darshanCommits]

Theres an option "Launch playerin a separate window (advanced)" that is a boolean. All it does is launch the player in mpv like window. It does not make use of the system mpv(which I want) but some barebones player that only has basic functionalities.

Dynamically selecting player or using the env var VIDEO_PLAYER should be the ideal choice (and to extend work done here to stremio-web #f5a0bc8)

tested on: nix pkgs, flatpak