Variable Frame Rate Check

Is your video variable framerate (VFR)? Find out here!

This in-browser VFR check will quickly analyze your file – without it ever leaving your computer.

What's a frame?

A video is just a bunch of pictures, called frames. They flash before our eyes fast enough that it looks like motion.

What is frame rate?

Every video has what's called a frame rate which is the number of pictures that get displayed each second.

Some common numbers for framerates are 23.98, 25, 29.97, 30, 59.94, and 60 fps (frames per second).

Why is constant frame rate best?

When it comes time to edit a video, most editing programs like Adobe Premiere and DaVinci Resolve make the assumption that every frame is the same length, also known as constant frame rate (CFR).

This makes it easy to do the math on the frames, basically. If you ask "hey, seek to time 10:37" a program can quickly figure out which frame that is, if every frame is the same length.

When they're not the same length, that math becomes a (slow) pain to do. If the frame length can change at any time, it would have to look at every frame before the time you asked for.

What causes variable frame rate?

Sometimes, a video's frame rate isn't constant. This is where variable frame rate (VFR) comes in. It's most common in screen recordings, video game captures, and some phone videos.

It usually happens because the recorder has trouble keeping up – and to make up for that, it stretches or squishes the time between some frames.

An analogy: How a video recorder works

Imagine you were working on an assembly line screwing caps onto tubes of toothpaste. Let's say you do one tube every 5 seconds, and that's great.

(the toothpaste tubes are the video frames in this analogy ... and the gaps between them are how long each frame should be displayed for. Bear with me here)

You're keeping up, everything is fine. And then you feel a sneeze coming on! You turn away for a split second to sneeze... but when you turn back, you see that 5 seconds have passed, and now you're behind! So you screw the cap on a little faster to catch up, and maybe you do the next couple a bit faster than usual too.

This is like what a video recorder is doing. If it hits any hiccups – maybe saving to disk takes longer than usual, the encoder hits a very detailed frame that takes longer than usual – it has to catch up by stretching or squishing the time between frames.

Why is the video out of sync with the audio?

Variable framerate videos usually confuse programs like Adobe Premiere. Their assumption that frames are equally-spaced goes out the window, and the result is usually a video that's out of sync with its audio.

The desync can happen immediately, or it can the audio can be in sync at the start, but then slowly drift out of sync over time. It all depends on how many frames are squished or stretched, and when. It's pretty much random.

How to convert to Constant Frame Rate

This tool will tell you if your video is variable framerate or not. If it is, you're best off converting it to constant framerate before editing it in most video editing programs.

You can convert to constant framerate for free using tools like Handbrake or FFmpeg.