I tried learning from videos from scratch about five years ago, and it seemed easy enough - just repeat the movements and you're good. The first two months were fine, but then my back started hurting. Turned out I was distributing the load wrong in forward bends because nobody pointed out what to pay attention to. Eventually I went to a trainer anyway - in one session he showed me a ton of nuances I wouldn't have found in videos for months.
My advice: YouTube videos are great, but do at least a session or two with someone who can give you feedback. You don't have to go for a whole month - even a couple of sessions will help you understand how to safely get into poses without risk. After that, videos will be way more useful because you'll already know what to look for. It's cheap compared to treating back problems later.