Much of the initial concern about the EOS 5D Mark IV's video has been about its substantial 1.64x crop (relative to the full width of the sensor, 1.74x compared to the 3:2 region) and its use of the inefficient Motion JPEG compression system (which limits the ability to use SD cards with any dependability).

However, upon shooting with the camera we found it to have significant rolling shutter. We've demonstrated the effect alongside the EOS-1D X Mark II, which reads out its sensor fast enough to exhibit pretty low levels of rolling shutter, and the Sony a6300, which shows a relatively high level of rolling shutter at 24p, albeit less so at 30p.

Detailed demonstration

Now we're allowed to show footage from the camera, we can show more clearly the difference between the EOS-1D X II, which showed very low levels of rolling shutter in our real world videography, and the EOS 5D Mark IV's footage, which we believe you'll need to be much more careful with. Particularly when it comes to using 4K video to shoot action at high frame rates, either for video or for 4K frame grabs.

Fast pan

EOS-1D X Mark II (60p) EOS 5D Mark IV (30p)

As before, these grabs were taken from a relatively fast pan with both cameras attached by an arm so that they're being moved at exactly the same speed. Unlike before, these were shot at 1/1000th of a second shutter speed, so reflect the behavior when trying to shoot for frame grabbing.

Slow pan

EOS-1D X Mark II (60p) EOS 5D Mark IV (30p)

These grabs come from a slower pan, much more like the kind you might wish to include in your own shooting. The 1D X II displays so little rolling shutter as to not be an issue at all at these speeds, while the 5D Mark IV continues to exhibit enough rolling shutter as to render a very odd looking frame grab.

What does this mean?

While rolling shutter isn't a huge deal at 1080p on the 5D Mark IV, 4K footage risks having panned or moving objects skewed diagonally across the frame and, potentially worse, a 'jello effect' to hand-held video. The jello effect can particularly show up in footage shot while walking, which isn't an unreasonable use-case for this camera for, say, wedding cinematographers. 

The 1D X II shows far better performance in this regard, and the ramifications extend beyond video shooting. We were - and continue to be - quite excited at the ability to use using the 1D X II for, effectively, 60 fps action shooting with (Dual Pixel) AF, thanks to the Canon's excellent 4K Frame Grab feature and very capable video AF. While you can do the same, albeit at 30 fps, with the 5D Mark IV, the reality is that the very fast action shots, or fast-moving subjects, that would benefit from the high frame rate of capture are the ones that will be most adversely affected by the decreased rolling shutter performance.

Ultimately, if you're careful with the way you move the camera, this rolling shutter effect may not be too apparent; however, there will be scenarios where it becomes distracting, at which point you may have better luck rolling the 5D Mark IV back to 1080p.