We typically encourage our clients to caption any video they put on the web. I do not know the exact metrics to SEO rank jumping based on captions vs non-captions. That could be a experiment for Moz and their lab. In my experience though, it's a benefit beyond just the simple SEO. It's about general accessibility.
1st off, Google will try and auto caption your video whether you want them to or not. Typically it does an absolutely horrible job. So if someone is trying to watch your video with captions, it may make little to no sense.
2nd, Google will take those captions and translate them into any language it needs. Much like a bad game of telephone, we have found that bad translations just keep getting worse as google auto translates them.
3rd, it's been mentioned a few times that google does in fact scrape and index captions. They are what tells google what your video is about because Google doesn't have the AI intelligence to watch and understand. At least not until it goes full skynet and takes over. Here are a few links that may help.
http://moz.com/blog/hosting-and-embedding-for-video-seo
http://www.reelseo.com/youtube-closed-captions-seo/
http://www.3playmedia.com/2014/01/10/future-accessibility-video-captions-according-google-youtube/
On an implementation note, there are a few different ways to ease the burden.
- If it's script based it's easily upload-able yourself. While youtube is fairly awful at understanding, it can listen and align pretty well. If we have a script we simple copy and paste and are good to go.
- Hire out a professional transcription subtitle person. We do these on large scale projects. They transcribe and send us a nice and clean .srt file that we upload directly to youtube.
- Errand services. I have had friends that use services like Task Rabbit to hire out people to do the work. Never underestimate the power of 50 bucks when someone can type up a few things from home while sitting in their underwear.
- INTERNS! I'm sure nothing pleases an intern more than to sit in a dark room transcribing video all day long. I'm fairly positive it's what they live for... at least that's what are interns say when we are not forcing them to battle to the death with nerf swords.
