Color Blotch: No kind of " interaction between the vibration frequency of the strings and the frequency of the video capture" can produce such asymmetrical effects on strings. Regardless of capture frequency, any single stopped frame shot by a camera that captures the image as a whole represents the actual shape that string has at that particular moment. A camera without rolling shutter effect would have captured strings as slightly curved lines. No kind of complex "oscilloscope-like" shapes actually run through strings, those are capturing effects caused by the fact that upper lines of the image represent different moment of time than the lower ones.
@JMartinP, so you mean the whole string moves as a whole, all of it goes to one direction of the other, the only standing wave is that of the fundamental tone, so there are no nodes, vibration modes and standing waves of harmonics?. You have just changed acoustics principles for ever.@Color Blotch, a string doesn't produce a sine wave, but the sum of many sine waves which are the harmonics of the fundamental tone, my arm is not flexible enough to do that. Maybe my granny's would, it's very wobbly :-)If the shutter speed is high enough you'll see the harmonics, if not they would blur out and you'll only see the fundamental and believe the string moves as a whole. It doesn't.
There are many videos on youtube where you can see the waveshape of guitar and other instruments:
The strings actually move in that "asymetrical" way. Strings and any other resonating object vibrate in many harmonic frequencies at the same time, and the actual shape of the string at any given time is the result of the addition of all those harmonics, resulting in the shapes you see. That's what's called timbre, and is what makes a guitar, a flute a trumpet and a violin sound different even if they are playing the same note, what is called the harmonic content.
The iphone video's effect has nothing to do with the rolling shutter, but on the actual capture of the string's shape at any given time, and the shape moving left or right is the effect of the phase difference between the string's vibration and the camera's frame rate, you would see the same effect if you lighted the strings with a stroboscopic light with the same frequency and burst duration of the camera.
Kiril Karaatanasov: ok this is misleading the cool effect of having sine is not due to rolling shutter at all.
On may blame rolling shutter for the distorted sine in the lowest string, though I think the cause is again in how different frequencies combine to produce something not seen.
Color Blotch's comment is wrong, see my reply to him