The RX100 IV marks a big step forward for video in this series of cameras. Video has always been something of a strength for the series, but the Mark IV brings changes that make it much more attractive to video shooters.

The most obvious change is the addition of 4K (UHD) video. This is useful regardless of whether you intend 4K to be your end-point. UHD is twice the size of 1080 in each direction, which means it can be downscaled to give much more detailed footage. Alternatively, it provides plenty of scope for punching-in or digitally correcting any camera shake, because you've captured so much additional information around a 1080 frame.

In addition to this, the RX100 IV gains several video features introduced in the a7S, that make video more attractive.

Video specifications:

The RX100 IV can shoot at a variety of resolutions and compression rates. The highest quality options utilize the company's XAVC S format, allowing the capture of 4K (UHD) at 30/25/24p at bitrates of up to 100Mbps, albeit with a small (1.09x) crop. 1080 footage can be recorded at 120/100p at 100Mbps or 60/50/30/25/24p at 50Mbps.

In 4K the camera can record up to 5 minutes of footage and the user should wait before re-starting (presumably to allow the camera to cool down). This means it's not the right camera for recording school plays or long speeches, but it shouldn't place too much of a restriction on videographers, who are likely to be cutting between multiple short clips. Only standard, optical image-stabilization is available for 4K footage.

The RX100 IV doesn't have a separate tab for movie options but most of the core settings are clustered together.

However, other options such as Picture Profile (Shooting Menu tab 6), Zebra (Custom Menu tab 1) and Peaking (Custom Menu tab 2) are scattered quite broadly.

The camera includes a wide range of support tools, including focus peaking and zebra, to make it easier to assess focus and exposure while recording. There are also some surprisingly high-end features, including the Picture Profile system introduced in more video-focused alpha 7S.

Sadly, the lack of Mic socket limits how good the camera's audio is going to be. This probably means having to buy and use an external recorder if you want good quality audio with your footage (something that makes a huge difference to viewer perception of quality).

Focus in video

There are some odd omissions, though: AF-S mode isn't available in video mode, so you can't use it to set focus before recording or to selectively re-focus during recording. Also, automatic focus magnification via MF Assist isn't available either before or during recording, so you'll need to assign it to a button if you wish to manually focus. That's a shame, as dedicating one of the precious few buttons - on a camera with the AF capabilities of the RX100 IV in still shooting - to focus magnifier is simply wasteful. Speaking of manual focus: the magnifier only gives you a 4x magnified view in video mode, as opposed to the 17.1x magnification for stills shooting.

An important update over Mark III is the availability of all focus areas area modes (previously, only 'Wide' was available). The tracking 'Lock-on' AF area modes are not available though, oddly, the separate 'Center Lock-on AF' function that requires a press of the center button to confirm the subject, is. This is awkward to access and awkward to initiate, compared with the area modes that just require a tap of the shutter button to start tracking. It's not clear why Sony has persisted with this two-tier system.

Face detection is also available in all video modes save for 120/100 fps. Eye detection, however, is not available in video at all.

This video shows two of the camera's main AF options in video: manually re-positioning the AF point and letting the camera rack focus between the two subjects, and Face Detection mode.

Although the camera can be a bit quick to jump, rather than smoothing progressing, between focus subjects, it's impressive how little it wobbles to check and re-check focus, so long as the camera and subject don't move too much. This is usually a problem for contrast-detection AF systems.

Video capture test

This still of our studio scene gives an idea of how the camera is capturing the scene. This varies, depending on the resolution you're capturing and whether you've engaged either of the digital image stabilization modes.

Image stabilization in video

One of the first thing you'll hear from anyone who's shot video with the latest RX100 cameras is 'I can't believe I got this footage from a shaky bus on dirt road!'. Indeed, 'SteadyShot' can be incredibly effective in video, as 'active' modes combine optical image stabilization (in-lens) with digital (electronic) stabilization to correct for most types of movement. Though not explicitly advertised as such, we suspect the 'active' modes to be capable of 5-axis stabilization, though roll is probably least effectively removed, as roll correction tends to cost a lot of resolution. Note that 'active' modes are not available in 4K, HFR, or 1080/120p video modes, which default to 'standard' optical stabilization only.

In the video below we shake the camera in various IS modes; have a look at how effective the various modes are.

Here we shake the camera to give you a look at how effective the various IS modes are. The bottom right inset is a video of us shaking the camera, while the main frame is the video from the camera being shaken.

'Standard' uses in-lens optical stabilization only, while 'Active' and 'Intelligent Active' use progressively more digital stabilization, at the cost of image cropping to yield smoother and smoother video.

You may have noticed the video crops progressively further and further in as we engage some of the IS modes. The diagram below shows the exact areas of the camera's different crops in the different IS modes, as well as the crop of the sensor used for 4K. The camera's Steadyshot Active and Steadyshot iActive modes crop further and further into the sensor, to let the camera capture more of a border around the main image frame, which can then be used if the camera is shaken.

100% crop from mode selected below.

As you can see, using the camera's digital stabilization has a resolution cost.
IS Off / Standard (Optical) IS Active IS iActive

120/100p modes

In addition to the high frame rate modes we'll discuss later in this review, the RX100 IV can also shoot at 1080/120p and 100p, depending on whether you're in NTSC or PAL mode. Unlike the High Frame Rate modes, you're not restricted to two or four seconds of shooting. However, the camera will also not slow the footage down to a more common frame rate for playback, so you'll have to slow them down in post-processing software if you want to use it as slow-mo footage.

And, because the camera is continuously shooting so many frames (potentially beyond the capacity of its DRAM buffer), several restrictions are placed on the mode: DRO, which tries to lighten shadows while protecting highlights isn't available. You can still use a relatively flat Picture Profile if you need to be able to incorporate a wide dynamic range into your footage, though. Face-detection and Center Lock-on AF are also unavailable, as are 'active' image stabilization modes, again likely due to the processing burdens.

Rolling shutter

We were curious about Sony's claims of decreased rolling shutter in video, so we mounted both RX100 III and IV cameras to a dual rail system and panned back and forth rapidly to look for any rolling shutter. We aligned the videos in Adobe Premiere and grabbed frames from each camera's video shot at exactly the same moment.

RX100 IV 60p RX100 III 60p
RX100 IV 120p

Note the more upright verticals, compared to the shot on the right
RX100 III 60p

Sadly, so far as we can tell, the promised rolling shutter improvement only appears to apply when using electronic shutter in stills mode and in 120 fps video. 4K video is highly prone to rolling shutter and most of the 1080p modes appear to offer little, if any, improvement when compared to the RX100 Mark III. Only 1080/120p shows a noticeable improvement.

The good news is that rolling shutter was already quite well controlled on the Mark III; however, if you are really concerned about minimizing rolling shutter, you'll want to avoid 4K and shoot in 1080/120p, after which you can either conform the footage to a lower frame rate by slowing it down (5x to 24p, for example), or convert it to 60p by dropping every other frame, or 24p by only keeping the 1st of every 5-frame chunk. 120p footage is surprisingly versatile that way.

Frankly, though, we're perplexed as to why lower frame rate (24, 30, 60p) HD video doesn't show any improvement in rolling shutter. Furthermore, the fact that 4K has significantly more rolling shutter than 1080p points to different read-out modes, which makes us wonder if 1080p employs some level of pixel-binning, whereas 4K reads more of the pixels which, then, results in slower read-out.