I sometimes watch movies/scenes with sutitles downloaded from this site.

SRT always works. VTT does not work with my TV.

Has anybody tested VTT succesfully with a TV? Which brand?

VTT does not work with my TV either.
The best way is to convert VTT into SRT.
TV supported only certain files and with certain rules.
For example, my TV can't display an SRT with two subtitles at the same time, my TV stop the video or turns off. But my SmartTV is old.

In reply to Lionfacial:

For example, my TV can't display an SRT with two subtitles at the same time, my TV stop the video or turns off. But my SmartTV is old.

I actually never tried that. Interesting thought.

Example:

movie.mp4
movie.en.srt
movie.de.srt
movie.fr.srt

Correct?

I never tried that.

I assumed only this syntax works:

movie.mp4
movie.srt

I think it works for me with MKV and subtitles within, but I guess that works for yours, too.

Sorry for the confusion, that's not exactly what i meant, it's more something like in the same SRT when you got two lines at the same time.