What is variable frame rate (VFR) and how does it work?

So, what is Variable Frame Rate?

Variable frame rate, or VFR as it is more commonly known, or Varispeed on some high-end professional cameras, is a term widely used within the film industry to shoot at a different frame rate to that of your recording/clip timeframe to achieve either slow-motion or speed ramping in-camera. 

So, in short, VFR, is a way to record internal slow-motion or speed ramping (speeding up) within your camera, and without having to work video editing magic later on when editing. How many frames per second you can record up to in VFR mode and in what codec is limited from camera to camera, so your mileage may vary. However, it is more common these days to see cameras record VFR to at least 120fps or above on higher-end models.

Example:

Let's say you want to record a time-lapse across a cityscape within your video camera. You have set a project for a 30fps timeline for your recordings, but you want this final time-lapse to look very fast in your final project. Using variable frame rate and recording this at, say, 15 frames per second means your camera will record half the frames you need in order to fulfil that 30fps requirement. Thus, when you play this footage back in-camera or on your computer, the footage will play back at double the speed at which you shot it.

So, a 10-second recording shot at 15fps on a 30fps timeline will actually be five seconds worth of footage, producing instant hassle-free speed-mapping that requires no technical knowledge in your video editing software. This is a pure record, drag and play option, which makes video editing later a more stress free experience.

To further understand frame rates and variable frame rates, take a look at this informative video by B&H that shows the true power of VFR and how you can use it within your next project to create captivating visuals:

This VFR effect/option can also be used for slow-motion, but rather than your recording being double the speed at which you shot it, it naturally becomes twice as slow. If you want to shoot a water balloon being popped in slow-motion, you can set your camera to record a VFR clip at twice the frame rate of your project, thus creating a 2x slow-motion playback in-camera rather than having to try to calculate frame rates and speed adjustments in a video editor.

It is worth noting that VFR is not implemented on every camera that can shoot video, but more commonly found on cinema cameras or prosumer cameras geared towards a “video first” approach. It can also be said that these effects can be done within the editing studio; however, when you start looking at your post production editing options, they are severely lacking when compared to producing VFR in-camera.

So why not go out and see what you can capture? You might even surprise yourself in how easy and laid back the VFR experience is, and it might even be your preferred method going forward.

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