Editor’s note:  This is the first in a series on iPhone 5s features.

The fact that the new iPhone 5s can record 720p HD video at 120fp is a big deal. Unfortunately, most people have no idea what that sentence means, so let’s break it down.


That pesky little option at the bottom of YouTube videos makes a world of difference, but what do those numbers mean? These numbers refer to the video resolution, measured in pixels.

Resolutions are described by the number of vertical lines displayed, and that’s exactly what 720 means. The 720 High Definition format is 720 pixels tall, by 1280 pixels wide.  The other common HD format you’ve probably heard of is 1080, which is (you guessed it) 1080 pixels tall, by 1920 pixels wide.

Video Resolutions ComparedWe live in a confusing world of video formats, but for reference, Standard Definition in the US is commonly referred to as NTSC and is 480 vertical lines. In other parts of the world it’s a standard called PAL, which is 576 lines.

Bottom Line: The bigger the number, the more pixels in the video frame. In most cases this also means better detail.

Frame Rate and Slow-mo

Slow-motion is awesome. Cool things tend to look even cooler in slow-mo. But how does slow motion become, well, slow? That’s all thanks to some fancy frame-work.

Let’s take a quick step back and remember that video is all an illusion. All that video consists of is lots of individual photos, or frames, shown quickly enough so that the brain thinks that the photos/frames are moving. Way back when (aka the late 1800’s) a few smart people discovered this trick, and soon enough motion pictures were born. (See? That name makes more sense now.)

What those brilliant folks discovered is that it takes at least 24 frames each second to give the illusion of fluid motion. That’s the frame-rate at which feature films are shown. TV in the US is shown at 30 frames-per-second (or FPS), and elsewhere in the world TV is shown at 25. There are fascinating technical reasons why, but that’s an in-depth for another day.

Overcranking Slow Motion

via Wikipedia.com

Back to slow-motion. There are a couple of ways slow-motion can be done, but the way the new iPhone does it is one of the most common. Video is shot at a higher frame rate than the rate it’s played back. This makes motion appear to move slowly. In our example up top, the new iPhone can shoot 720p video at 120 frames per second. When you play that footage back at a normal frame rate, for example 30fps, it will appear to move four times slower than normal.

Bottom Line: Slow-mo can be achieved a couple of ways, but the iPhone does it by shooting at a high frame rate.

So what can the new iPhone do?

Like iPhones before it, the 5s can shoot 1080p HD video at 30 frames per second. While this isn’t uncommon among consumer devices, the iPhone 5s delivers great video quality at this normal speed. What’s really remarkable is the new slow-motion feature.

Shooting at higher frame rates used to be possible by cranking a film camera at a faster speed than normal, hence slow-motion’s traditional name of overcranking. As film was replaced with sensors, overcranking was only achievable at low resolutions due to the high data rates needed. Alternatively, cameras may shoot at HD resolutions, but only offer slightly higher frame-rates, like 60fps. The iPhone 5s however, shoots at a remarkable 120fps without sacrificing quality at 720p HD.

You can now carry a device with you which, in addition to being a great phone, can bring out the true detail in life by slowing it down 75%. And we all know that a high-five viewed four times slower than normal is also four times more awesome than normal.

[youtube http://www.youtube.com/watch?v=xOUP_H4s9TQ&w=425&h=350]

What do you think of the new iPhone’s camera? Have slow-motion videos to show off? Share them in the comments below!