I've played around with flying videos and even the most expensive "helmet cameras" were of crap quality compared to even a cheap consumer camcorder.
Their advantage is small size and being waterproof, but while fixing a camera outside the aircraft improves the image quality considerably, it is easy only on some types, and is always illegal (on a CofA type) unless signed off by the right people so you can't go around doing it overtly.
Also all the helmet cameras suffer from prop effects caused by very fast shutter speeds. These can be minimised with a neutral density filter which forces a slower shutter.
The last mini camera I used was the Sony HQ1 (from Dogcampro) which was used to make
this video (flying into Tempelhof). IMHO the quality is crap, and that is after cropping it a bit to remove the worst distortions (which were
not caused by the aircraft window).
There was a much more pricey helmet camera, from Sony too, at about £1000 but I never found anybody who had stock.
For a comparison,
this video came from what today would be a £250 camcorder. Take your pick
Using a camcorder is easier nowadays because they have enough storage to run on their own for hours. The old DV ones could not run for more than an hour so could not be set up and started on the ground and just left. They had to be either messed with during the flight (bad news if you are busy) or wired up in the "showroom demo" mode whereby providing it with constant external power and switching it to Record provides a nonstop video output, like a high quality webcam.
A high Q webcam is another way to approach it but I have found the quality poor also. I also started to experiment with taking a still pic (with the webcam) every second and then combining them into 25fps movies, which gives you a 25x speedup and can be fun for filming a whole flight which would otherwise be mostly boring.
This one (a flight from Brac, Croatia to Canakkale, Turkey) was made with the most expensive webcam - the £50 Micro$oft USB one. Note the prop effects. I removed it from the top of the panel pretty fast after landing, just in case, this being Turkey
If you are happy with this quality then this is easy because it just plugs into any laptop, etc. and there is any number of little progs which can take a snapshot ever 1 sec and save it to a 640x480 jpeg, and then you combine the jpegs into a movie using Premiere etc etc. or you could use windoze movie maker to just record the whole movie (a few MB per second) to the hard disk of the laptop but then you have the job of editing it.
A camcorder is also totally self contained, whereas any of the other solutions involve wires, power supplies, etc, unless you go for one of the solid state recorders which places like Dogcampro sell (not cheap).