Originally posted by watchingskyfallatm - would you recommend the K-3 for someone shooting primarily video?
Sorry to say but Pentax isn't up to par with most other brands regarding video, you can get great results with a K3 for sure (even the K-50 isn't all that bad) but it is not your best option for the price IMO.
Originally posted by watchingskyfallatm - should I get the K-3 instead of for example a second-hand 5D mkii?
The 5DmkII is still regarded as great for video. But proper lenses for it will cost you.
Originally posted by watchingskyfallatm - does it matter that it's not full frame?
Not touching this one...
Originally posted by watchingskyfallatm - for those of you who shoot a lot of video, what are the advantages/disadvantages?
Again, someone else could elaborate on this one
Originally posted by watchingskyfallatm - are there AA battery pack converter thingies available for the K-3? Ie the ones that take 3 AAs and slide into the battery compartment? Or would I be looking at one of those base-mounted things?
You need to get a battery grip to be able to use AA... 6 of them by the way (and 4 for the K-50, not 3) But if you're planning on using only for video, you should consider an AC adapter.
Originally posted by watchingskyfallatm - any other advice/suggestions?
At the moment Panasonic gets a lot of hype with their GH4, even the older GH3 will give you very good results. Being an M4/3 it opens you to a whole whack of lenses from a lot of manufacturer. And with a proper adapter you can use pretty much any lens on it.
It looks like you want to "up your game" but you should ask yourself what you really need. A 5DmkII or mkIII can give you close to motion picture quality footage but isn't it a bit overkill for youtube? I for one still watch Youtube video @ 360 to save bandwidth... You should also think of what you are looking for, AF while shooting? Better video format/compression/RAW? 4K? Stepless exposure controls? Compatibility?
The camera plays only a minor part of the end result... Lenses, lighting, technique, composition, post production will have a greater impact. There are amazing videos shot with very low end cameras or with smartphones