The iPhone 7 Plus and Pixel XL capture some of the best 4K video coming out of a smartphone. The Pixel tends to record a little more detail, but is a tiny bit noisier. Oddly, it is the iPhone that has the noticeably warmer output in video, with the Pixel remaining neutral - it was the other way around in stills.
Both smartphones record mono audio, which is at odds with their flagship status. Still, the iPhone did a somewhat better job with noise cancellation - some heavy winds in the following two videos shots side-by-side and the Pixel XL is noticeably noisier.
iPhones have been revered for their excellent electronic image stabilization, and the iPhone 7 Plus does indeed set the standard in this respect. The Pixel could have snatched the crown here as well though, as it does an equally good job of stabilizing both small vibrations and global movement. The issue is that it exhibits abrupt jolts every now and then as the processing catches up with reality. This will obviously vary with hand steadiness, walking style and subject matter, but we did observe it in our time with it.
In low light the videos from both phones get noisier, naturally, but the Pixel tends to hold on to detail noticeably better. Check out these videos shot at dusk.
As befitting a flagship, these two deliver excellent 2160p video footage, with the high levels of detail and very good stabilization when shooting handheld.
Video winner: Tie. The Pixel scores points for detail and color rendering, but the iPhone's stabilization is superior, as is noise cancellation.