There's also the problem of content which doesn't have subtitles to begin with---YouTube's automatic subtitle generation is great, but could be improved and expanded to languages other than English.
It is expanded, at least to Japanese. What's also fun is you can then have it auto translate the auto generated subs. The results are... not typically great, but the potential!
A long time ago, I tried the "autosub" feature with anime and it replaced understanding with unintentional (dry) humour. The output had phrases that resembled a news transcript, which is probably what they were training the system on.
FTFY