Hi Eduard,

I do see that part of the code. But what should I do ?

This is the content of the css style:

.flowplayer { border: 1px solid #ff0000 !important; }

.flowplayer { margin: 0 auto 28px auto; display: block; }
.flowplayer.fixed-controls { margin: 0 auto 58px auto; display: block; }
.flowplayer.has-abloop { margin-bottom: 52px; }
.flowplayer.fixed-controls.has-abloop { margin-bottom: 82px; }
.flowplayer.has-caption, flowplayer.has-caption * { margin: 0 auto; }
.flowplayer .fp-controls, .flowplayer .fv-ab-loop, .fv-player-buttons a:active, .fv-player-buttons a { color: #eeeeee !important; background-color: #333333 !important; }
.flowplayer { background-color: #000000 !important; }
.flowplayer .fp-duration, .flowplayer a.fp-play, .flowplayer a.fp-mute { color: #eeeeee !important; }
.flowplayer .fp-elapsed { color: #eeeeee !important; }
.flowplayer .fp-volumelevel { background-color: #3413bb !important; }
.flowplayer .fp-volumeslider, .flowplayer .noUi-background { background-color: #eeeeee !important; }
.flowplayer .fp-timeline { background-color: #666666 !important; }
.flowplayer .fv-ab-loop .noUi-handle { color: #333333 !important; }
.flowplayer .fp-progress, .flowplayer .fv-ab-loop .noUi-connect, .fv-player-buttons a.current { background-color: #3413bb !important; }
.flowplayer .fp-buffer, .flowplayer .fv-ab-loop .noUi-handle { background-color: #eeeeee !important; }
#content .flowplayer, .flowplayer { font-family: Tahoma, Geneva, sans-serif; }
.flowplayer .fp-dropdown li.active { background-color: #3413bb !important }

.fvplayer .mejs-container .mejs-controls { background: #333333!important; }
.fvplayer .mejs-controls .mejs-time-rail .mejs-time-current { background: #3413bb!important; }
.fvplayer .mejs-controls .mejs-time-rail .mejs-time-loaded { background: #eeeeee!important; }
.fvplayer .mejs-horizontal-volume-current { background: #3413bb!important; }
.fvplayer .me-cannotplay span { padding: 5px; }
#content .fvplayer .mejs-container .mejs-controls div { font-family: Tahoma, Geneva, sans-serif; }

.wpfp_custom_popup { position: absolute; top: 10%; z-index: 20; text-align: center; width: 100%; color: #fff; }
.wpfp_custom_popup h1, .wpfp_custom_popup h2, .wpfp_custom_popup h3, .wpfp_custom_popup h4 { color: #fff; }
.is-finished .wpfp_custom_background { display: block; }
.fv_player_popup { background: #333333; padding: 1% 5%; width: 65%; margin: 0 auto; }

.wpfp_custom_ad { position: absolute; bottom: 10%; z-index: 20; width: 100%; }
.wpfp_custom_ad_content { background: white; margin: 0 auto; position: relative } .wpfp_custom_ad { color: #888888; z-index: 20 !important; }
.wpfp_custom_ad a { color: #ff3333 }

.fv-wp-flowplayer-notice-small { color: #eeeeee !important; }

.fvfp_admin_error { color: #eeeeee; }
.fvfp_admin_error a { color: #eeeeee; }
#content .fvfp_admin_error a { color: #eeeeee; }
.fvfp_admin_error_content { background: #333333; opacity:0.75;filter:progid:DXImageTransform.Microsoft.Alpha(Opacity=75); }

.fp-playlist-external > a > span { background-color:#808080; }
.fp-playlist-external > a.is-active > span { border-color:#bb0000; }
.fp-playlist-external.fv-playlist-design-2014 a.is-active,.fp-playlist-external.fv-playlist-design-2014 a.is-active h4,.fp-playlist-external.fp-playlist-only-captions a.is-active,.fp-playlist-external.fv-playlist-design-2014 a.is-active h4, .fp-playlist-external.fp-playlist-only-captions a.is-active h4 { color:#bb0000; }
.fp-playlist-vertical { background-color:#808080; }

.flowplayer .fp-subtitle span.fp-subtitle-line { font-size: 16px; } .flowplayer .fp-subtitle span.fp-subtitle-line { font-family: inherit; } .flowplayer .fp-logo { bottom: 30px; left: 15px }
.flowplayer .fp-subtitle span.fp-subtitle-line { background-color: rgba(0,0,0,0.5); }

Hi! Thank you both for your help, were else can I find such support!

Martin, you were right: the loader animation is due to a conflict with something in my setup. After your suggestion, I tested it on my personal website and the loader was showing.
I use WPLMS theme, so I tried to disable many plugins (not all though, but all the wplms ones and others), I also try disabling all my custom css: still no loader.
I switched to the twenty fifteen default theme, but then I got a javascript error on all videos so I couldn’t test if the conflict was caused by wplms theme. By inspecting the code I managed to get the loader showing by adding this css, so it works now! (the opacity was on 0 somehow).

.flowplayer .fp-waiting em { opacity: 1 !important; }

Alec, thank you so much for your help and for taking the time to test further! Just so Martin doesn’t worry too much lol:
– My loader is now working :-)
– There was no subtitles on all the videos you tested: we only subtitle artist masterclasses. (I recorded all the courses videos in both language -sorry for the english- so when people switch language, the video speaking is in the chosen language). Here is a link to a test page I had with subtitles at the very end, see if they work on your side pls:
https://harp-school.com/flowplayer-test/
– The links not working under the videos is because they point to the course units which are only accessible for subscribers. And the plus on the right are default theme icons I have to replace.. Thanks for your feedback, I take note that for someone new it could look like an error.
– The “html5: Unsupported video format” you got on firefox is not cool though. All the videos are loading fine on my end (chrome, firefox and safari, pc mac iOS android)… But, and this is something I wanted to report in a new topic: sometimes if I launch a video and go to another tab or app while it loads, I would get these errors messages and have to refresh page. It is not all the time so I’ll try to find the exact scenario.

Thank you again for your time, I am a very happy with your player, and super-confident in my choice, as above the very high quality of your plugin, your support is amazing! Cheers from sunny south of France!