I've always found yoga by video frustrating, since I find it hard to follow and be sure I'm in the right position. I'd recommend at least doing a class or two to start if possible. Beyond that, it's a matter of figuring out what kind of yoga you are interested in. One mistake I made with videos was doing a "fitness yoga" class that included a bunch of traditional bodyweight exercises which is great except that I am doing lots of pushups and such at other times.

One option is to search around on the internet for recommended yoga sites. However, one that was recommended by Jen Comas Keck when she was interviewed on the Fitcast was YogaGlo, which sounded really good so I took note of it (haven't tried it yet).

I think you have to subscribe but there may be trial options or sample classes--I haven't explored it yet so am not vouching for it, just saying it might be worth looking at. It gives a lot of choice for the type of yoga and class and then has filmed classes.

A little something from Jen on yoga (if you aren't familiar with her, also to her site): http://www.jencomaskeck.com/2014/04/you-cant-be-good-at-yoga-and-other.html

The Bad Yogi site is fun and educational too. I've found it helpful in correcting my form on some poses.

doyogawithme.com is a FANTASTIC resource for at-home videos. It's free and you can search by class length, class type, instructor, etc.

In all seriousness, though, I would strongly urge you to look into drop-in rates for yoga classes. A lot of studios, especially near college campuses, will also have occasional freebies (say on Sunday nights) and that's a good way to get some foundation in what the poses should look like, breathing, etc. Even classes through your local Y can be good depending on who's teaching, and there's a lot of value in having someone there who can check your form.

I've just started Hot Yoga (38 degrees) once a week and am loving it. It's a 60 min class which is perfect for me as I don't like to meditate/hold a pose too long (boring) so a 60 min class moves through the transitions quicker. Am hoping to improve my flexibility & mobility.