OneTaskBy Tim King · Updated
Frame Rate Detector
Find a Video's FPS and Check for Variable Rate
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How the Frame Rate Detector works
This frame rate detector plays the start of your video silently, times every frame and tells you its fps, snapped to the nearest standard rate such as 23.976, 25 or 29.97. It also shows whether the clip is constant or variable frame rate. The video is read in your browser and never uploaded.
Frame rate decides how motion looks and whether clips will cut together cleanly. Mixing 25 and 29.97 fps footage on one timeline causes stutter, and variable frame rate clips from phones and screen recorders are the most common cause of sound drifting out of sync in editors.
How the frame rate detector works
Browsers do not reveal the frame rate stored in a file, so the tool measures it. While the clip plays muted, the requestVideoFrameCallback API reports the media timestamp of each frame as it is shown. The detector takes the gaps between those timestamps and uses the median, which ignores the odd frame dropped by a busy computer. One divided by the median gap is the measured rate. If a standard rate lies within 1.5% of it, that rate is shown.
Constant or variable frame rate?
In a constant frame rate (CFR) file every frame lasts the same time. In a variable frame rate (VFR) file the gaps change, often dropping to half speed in dark scenes or when a screen recording shows nothing moving. The detector compares the gap at the 90th percentile with the one at the 10th; if they differ by more than 20%, the clip is reported as variable.
| Rate | Typical source |
|---|---|
| 23.976 / 24 | Cinema, streaming drama, many cameras' "cinematic" mode |
| 25 / 50 | TV and video in Europe, Australia and other PAL regions |
| 29.97 / 30 | TV in North America and Japan, most phones by default |
| 59.94 / 60 | Sports, gaming, smooth phone video, screen recordings |
Tips and pitfalls
Longer samples are more reliable. Two seconds is enough for a clean camera file. Use 10 or 30 seconds for screen recordings or anything you suspect is variable.
A slow computer can drop frames. Dropped frames appear as long gaps. They do not change the median, but if the gap range looks wild, close other tabs and press Measure again.
High frame rate clips. Some displays refresh at 60 Hz, so a 120 fps clip may only show every other frame and measure as 60. Slow-motion phone clips are often stored at 30 fps anyway.
How to read the result
Frame rate is the answer to use in editors. Type tells you whether to convert a clip to constant rate first. Download saves every frame's time and gap as a CSV for a closer look.
FAQ
How can I tell what fps my video is?
Drop the file here. The detector plays a few seconds silently, measures the time between frames and shows the frame rate, snapped to a standard value such as 24, 25, 30 or 60 when the measured figure is within 1.5% of one.
What does variable frame rate mean?
The frames are not evenly spaced. Phones and screen recorders save power or space by holding frames longer when little changes. Editors expect even spacing, so variable clips can drift out of sync with their sound over a long timeline.
Why does it say 29.97 instead of 30?
North American TV slowed its 30 fps rate by 0.1% when colour was added, and the standard stuck. Most phones and cameras in that region record at 29.97 fps, which is 30000 frames for every 1001 seconds.
Is my video uploaded to measure it?
No. The video plays in your own browser and only the timing of each frame is recorded. Nothing is sent to any server, so private footage stays on your computer throughout the whole measurement.
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