The thing about transcribing is that it's not always going to be easy. When I did transcription work, I remember doing subtitles for a couple ads, and those were just two minute videos. But here's the problem, sometimes it's hard to tell what a person is saying in a video. Due to that, you may have to re-listen to the audio over a few times to get the subtitles as correct as possible.
There are some sites that pay you to transcribe. I forget what site it was I worked on, but it was a legit one, one of the popular ones I'm sure. And for the work you do, I don't know if it's really worth the time. There is some audio that is tough to decipher and you can get stuck on short audio/videos. I stopped doing it, because I realized it needs your utmost attention and it can take a while to get the transcription 100% as good as you can get it.
Some audio you won't be able to get, so you have to mark it in the subtitles as unknown or unrecognizable. But a lot of these services want the best transcriptions, because I think as you work on, you eventually get work on movies and tv. I don't know if I could handle working on movies or tv, though it would probably be a lot easier to understand the audio.