A video shot in slow motion often has problems with flicker. It’s common that light fluctuations that you can’t see with the naked eye show up when shot at high frame rates (slomo) like 240fps or 480 or even higher. The lights may be of poor quality or the electrical current may fluctuate more than normal and the resulting video will need to be deflickered.
So we get asked a lot about how to fix flicker in slow motion footage. In this post I’ll discuss using Flicker Free to deflicker the video. There are examples of most of the host apps we support: After Effects, Premiere Pro, Davinci Resolve and Final Cut Pro.
You can download Flicker Free here
TL;DR
I’ll go into more detail below but for those that just want to try something quick:
With slow motion, the flicker can be very fast or very slow. So deflickering may require different approaches.
- See if one of the presets fixes the flicker.
- If not, start with the default preset (Rolling Bands) and turn off Detect Motion
- Even if it’s blurry, is the flicker gone? Then try to fix the blurring.
- Turn on Motion Compensation
- If that works, and flicker is very fast (e.g. every other frame) try setting Time Radius to a lower value to speed up renders.
Alternatively, sometimes with flicker that is slower, say flickering over 10-20 frames, you may need to increase the Time Radius or Time Step to increase the time range Flicker Free is looking at. i.e. Time Radius of 7 will look at 7 frames before the frame being analyzed and 7 frames after for a total of 1/2 second of video (@ 30fps). If you increase Time Step to 2, that will double the time range to one second, as it will look at every other frame instead of every frame.
However, the more frames you’re looking at the slower it will render and the more chance for artifacts like blurring, which will require Detect Motion or Motion Compensation turned on (or both).
The above instructions will fix the flicker for a lot of footage but you may need to dive deeper into the settings.
The Nitty Gritty Flickery Details
Alright, let’s go more in depth.
Rather watch a video than read? Here are video tutorials for some of the different host apps we support! (or scroll down to read)
Davinci Resolve Premiere Pro
After Effects Final Cut Pro
Let’s check out Flicker Free.
Again, you want to start with presets. These are just collections of settings that we’ve found to work on some footage. Don’t get too hung up on the names. The Stage Lights preset may work for slow motion footage and the Slow Motion preset may not, but will work for neon lights. Try them out and see what happens.
If none of the presets work for footage, start with the default Rolling Bands preset.It’s sometimes helpful to turn off Detect Motion and increase the Time Radius just to see if the footage gets deflickered. (it might be blurry)
To deal with blurring, use Detect Motion, Motion Compensation or both. They work differently and sometimes one or the other will work fine and sometimes you need both. Detect Motion renders faster, so start with that.
A lower Time Radius will also reduce the chance of artifacts or blurring. This tells Flicker Free how many frames to look at. The more frames you’re looking at, the more chance for blurriness or other problems. So a lower value is helpful if it works.
Time Radius also increases render times, so again, the lower this is set, the better. If you have very fast flicker you can sometimes get away with setting this to 3 or 4 as we did with the football footage in the above videos.More often a value of 8 works pretty well but for slow flicker, flicker that happens over a long time period, you may need to increase Time Radius and/or use Time Step.
Time Step is a new feature. It’s a multiplier for Time Radius. For example, if it’s set to 2, it doubles how much time Flicker Free is looking at. i.e. a Time Radius of 7 will look at 7 frames before the frame being analyzed and 7 frames after for a total of 0.5 second of video (@ 30fps). If you increase Time Step to 2, that will double the time range to one second, as it will look at every other frame instead of every frame. If you increase it to 3, it’ll look at every third frame (and triple the time range to 1.5 seconds.
If you’re still struggling, you’re welcome to send us a few seconds of the footage and we’ll recommend settings. Email us at cs@digitalanarchy.com
