How lighting conditions can induce a different per-frame exposure time in a camera and cause a stroboscopic + rolling shutter effect, well visualized by this gif [source: https://buff.ly/2X5Oo0i ]pic.twitter.com/PBvMnPyKyx
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Yes exactly, common confusion between frame rate and shutter speed. When the light gets brighter the camera adjusts to a faster shutter speed, thus freezing each frame and revealing the rolling shutter effect that was previously hidden by motion blur.
Worth noting that the frame rate *can* change. Once the lighting gets dark enough that the shutter speed is slower than the frame rate, the frame rate drops too. Either the file ends up with duplicate frames, or missing ones (modern video formats support variable frame rates).
