Problem is solved. I have changed "&$player" to "$player" in the C:\xampp\htdocs\lc.radiologos2023.sk\plugins\sermonspeaker\jwplayer7\jwplayer7.php (line 74). Beacuse it is Joomla 3 plugin, I dont care.
And I have installed MediaElement.js plugin. SermonSpeaker now works.
