You've probably done it dozens of times if you've done it at all. You know, accidentally started recording video when you didn't mean to. If you're lucky, you only ended up with a five-minute sequence of the inside of your camera bag, or upside-down landscape bobbing and bouncing as you saunter along unaware that the camera is merrily recording every moment.
If the video gremlins have been up to their usual mischief, it probably used up the rest of your tape and/or batteries. But if they've been particularly unkind, you find that unfortunate sequence instead of what you really wanted. You remember that feeling as you play it back for the first time: your heart crawls up your throat as you see the camera being brought unsteadily to bear on your subject, and them bam! ... it ends at exactly the moment you wanted to record.
Now, granted, most video cameras ding or play some audio sequence to let you know you're about to start recording. Except that in a noisy crowd—say, at an amusement park, or in a noisy gathering—you just can't hear it.
And there may be an icon that appears in one corner or another to let you know you're recording. Except that your attention may be on keeping the subject in-frame, and you may not notice the absence of such an icon way off in the periphery.
So the problem persists.
Well, the problem exists because the same gesture is used to start recording as to stop it, namely, pressing that small red button. And by accidentally pressing it, the camera changes state on you, so the next time you press the button with intent, the outcome is not what you intended.
You thought you were starting to record, when in fact you were stopping.
Now in a critical environment where the stakes are higher, such an interaction—namely having the same gesture do an action and its opposite —would simply not be allowed to exist. Could you imagine, for example, pressing the same button in the same way to put your car into drive and reverse gears?
Ooops! I thought I was backing out of the garage, but...
Or, by the same token, the same pedal applying both gas and the brake? Imagine how many more accidents there would be. Fortunately, the auto industry has learned that a single control that toggles opposites in such a high-risk environment is plain old bad design, so it isn't done.
But video cameras continue to do so to this day. I'm guessing this is out of habit: the first camcorder of yore—or maybe the first popularly successful one—had a single button, and all the rest have followed suit in a me-too sort of way. The camera manufacturers aren't sweating bullets over this: you go through more tapes (good for them) and you're more likely to buy that backup battery (also good for them.)
And even now, I can imagine designers of such devices playing blame-the-user: "Look, we make it ding, and we show the icon. You just need to pay attention to these clues to avoid this condition." That's true, we could do all these things.
But we don't exist to serve the camera. We're busy doing other things, and the camera exists to serve us, so it should be accomodating our needs ... and our shortcomings, (namely of attention, and time at that crucial moment we're hoping to capture.)
So, what's the alternative? I'm thinking a simple rocker switch—such as the zoom control uses—would do the trick. Flicking it up starts recording, and flicking it down stops recording. No more missed video turning the recorder off when you wanted to turn it on.
Two distinct gestures for two opposite actions.