The height of the spacing above the thumbcaption is slightly higher than intended.
https://ru.wikipedia.org/wiki/Википедия:Форум/Технический#Лишний_зазор_в_видео-миниатюрах
This is because .mw-tmh-player is set to be an inline-block element, because audio/video elements are inline elements so we want this behavior for those outside thumb frames.