I tried all sorts of makeshift video solutions: three digital cameras with good video capability; then my iPhone; various mounts on the bike and body. None of 'em was satisfactory.
So I finally broke down and got a proper video camera. It works much better.
Mine is an Ion Speed Pro, but there are others for under $100: Contour Roam; Polaroid; at least half a dozen knockoffs of GoPros under various names. And many more inexpensive dash cams.
Some will be weatherproof as-is. Others will need a rainproof housing. Some use self-contained batteries, others - notably dash cams - need an external pack.
I record almost every ride. Most are boring and uneventful. Sometimes I just delete everything. Occasionally I'll save them via Lightroom with a tag or keyword for "junk" or "delete" so I'll know a few months later which files to quickly identify and delete to make more room on the external hard drive. The videos I save that are boring are to prove where I was and what I was doing in case there's a complaint. For example, if I stop to snap some photos along the way I'll keep those videos for awhile in case some ninny files a police report complaining about some guy "spying" on his wildflowers.