I've been a bit surprised by how quick the GoPro and Yi camera battery runs out of juice...

So is it a good idea to direct power from PDB / BEC 5V regulated power ?

Yes you should be fine doing that, good things are:
you save the weight of the camera battery which is normally around 20-30g
never run out of battery as long as you are flying

downsides would be
ejecting your gopro in a crash and corrupting the footage. Other than that you save weight and don't have to worry about swapping batteries.
Also you cannot switch on the camera until quad is powered on...

you will waste some energy for converting from LiPo voltage to 5V with your PDB voltage regulator.
Plus, the Yi gets hot when recording with TV out and charging.

Also be aware / check first if your PDB can supply that amount of current for the camera on top of your FC/RX/OSD etc... so you don't upset those devices.

GoPro or Yi normally draw more than 500mA current, plus your other stuff that's more than 700mA... i think it would kill most of the PDB on the market with linear BEC hehe...
Just be careful with over heating if you decided to do that. or maybe get a dedicated switching BEC for your camera (although then you don't get much of the benefit of weight saving)

If you're not doing it for weight reduction i would recommend getting something like this which will allow you to simultaneously charge 3 batteries but also comes with 2 batteries allowing you to have 3 times the recording time. Hope this helps

http://www.amazon.co.uk/Smatree-Replacem...ro+battery

To put a GoPro on my new 180 quad, I definitely want to ditch the battery. I'm planning on powering it through the GoPro's USB port, from the 5V BEC on the Matek 5-in-1 PDB. It's rated for 3A. My Vtx runs directly off the (LC filtered) flight battery, and the HS1177 cam runs off the Vtx, so the only 5V amp draw I have is:

- Flight controller: about 100mA
- X4R: about 100mA
- GoPro 3: 500mA (https://gopro.com/support/articles/what-...e-charging)

So less than 1A from a 3A BEC… I'd say that's a safe margin  

I already have the cable from HobbyKing and have tested it on the bench off a spare ESC… yep, the GoPro powers up from 5V and records video.

I like the whole concept of powering the cams from the lipo, but I consider it impractical on a race quad, or rather any quad. hex etc that you plan on flying proximity.
My GoPro's take a solid beating and just about every part of it has scratches, dents and to have a usb plug hanging out the side is just asking for trouble..You crash, tumble 6 milion times and the usb plug snaps off inside the gopro and meanwhile active wires are waving all over the place just waiting to touch the carbon fibre frame of the quad, resulting in Chernobyl.

But..I do have a very vivid imagination. :-)