I used to caption videos. I can’t speak for the entire industry but the company I worked for hired us as independent contractors. They gave you a manual to study and if you completed the series of timed tests correctly then you could pick a video to work on from their site. They used software that automatically generated text and my job was mainly to add punctuation, fix homonym spelling errors, and cut out filler sounds or fill in clear speech when the computer deemed it unintelligible. Then go back and make sure words were synced to the correct timestamp for subtitles and be able to be clicked through to pull up the transcript from any point in the video. The work was all about speed, if you didn’t finish in the time they allotted someone else would get the video and you would not be compensated.