Squat Form Check

I am trying to do Olympic squat and front squat cuz I have some lower back issue. I have some problem to keep my torso upright, I think it’s because of the poor ankle mobility makes me have to lean forward to keep balance. My toe will automatically slide out a bit when I trying to squat deeper than parallel, according to Kelly Starrett (mobilitywod.com), it’s a sign of lacking ankle mobility.

I did some mobility drills in the beginning of the vid, just wanna give you an idea if I have any lack of mobility. Please critic my form and please give me some advice on how to squat deeper and more upright. Thanks!