If it helps, I tried to launch your project from my smartphone and it works (mobile Google Chrome)!
I think it is a browser compatibility issue. Technically, you can try to make the video play in all browsers, but it's actually more of a technical work, not the localization, and it could be challenging.
Eh… I guess in its current state it’s fine. Besides… don’t people watch videos MOSTLY on mobile devices anyway these days? If my project is fully operational on mobile devices… good enough for my first audiovisual translation 😊 Buuut… just out of curiosity: what exactly would I need to do to tackle these browser compatibility problems? Have also an .srt copy of subtitles ready or what…? Apparently some browsers just WON’T ACCEPT WebVTT. Only SRT. (There are also others, but these are even more niche?)Or is it a programing thing? I don’t know! Advice will be appreciated 🙂
As far as I know, it's more about coding the video player with compatibility in mind 😅
For example: https://developer.mozilla.org/en-US/docs/Web/Media/Audio_and_video_delivery/cros...
