I want to use a Canon T4i for vlogging and I wanna know how the autofocus works... is it automatic during recording ? And how do the modes work and what do they do? Thank you
It does have auto-focus in video recording. It has an early version of the hybrid AF. For your vlogging, are you looking for smooth fast video focus or are you mostly going to be sitting there like a news person?
If you are moving not too much or moving slowly, the the t4i can get it done.
If you are wanting very good AF, I suggest you get a different camera. Which one will depend on if you want to record over 30 minutes.
In general the best SLR types for video are the Panasonic GH series. The GH3 does 1080p, the gh4 and 5 have 4k support. The GH3 is quite a lot cheaper. If you are going to be walking around, take some time to consider what sort of vlog you want to produce. You might need stabilization (tripod, steadycam, etc) unless you want a jerky sea-sick like video similar to The Blair Witch Project.