Frames & rate
By target duration (optional)
Enter a duration to see the frame count it needs.
Length
- 4n+1 (Wan)
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- Interpolated frames
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- Final fps (same length)
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- Frames for target
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Length = frames ÷ fps. Wan-style models accept only 4n+1 frame counts (e.g. 81); interpolation ×N gives (frames−1)×N+1 frames at N× the fps for the same length.
A calculator that instantly converts between frames, seconds, and fps (frame rate): seconds = frames ÷ fps, and frames = seconds × fps. It's simple math, but doing the division by hand every time you generate Wan/Hunyuan video in ComfyUI, or trim a timeline in After Effects or Blender, gets old fast. Type in a frame count and fps and the length in seconds appears right away; enter a target length in seconds instead and it works backwards to the frame count you need. It also covers a couple of AI-video specific frictions. Models like Wan 2.1/2.2 only accept frame counts of 4n+1 (a multiple of four plus one, e.g. 81 frames), so the tool checks whether your frame count qualifies and, if not, shows the nearest valid frame count above and below — handy for landing on 81 or 121. Frame interpolation (RIFE and similar) changes both the frame count and the fps, so enter an interpolation factor (×2 / ×4) and it computes the interpolated frame count (frames inserted between adjacent frames) and the final fps (fps × factor) for smooth playback at the same length. It's pure calculation with no external API or data, so the numbers you type are never sent anywhere — everything runs locally in your browser.
How to use
- Enter a frame count and fps (frame rate); the length in seconds shows instantly.
- Generating with Wan? Check the 4n+1 status and snap to the nearest valid frame count (e.g. 81) if needed.
- Enter an interpolation factor for the interpolated frame count and final fps. Enter a target duration to get the frames needed.
FAQ
How do you convert frames to seconds?
Length in seconds = frames ÷ fps. For example, 81 frames played at 16 fps is 81 ÷ 16 ≈ 5.06 seconds. Enter a target duration instead and it shows the frames needed = seconds × fps, rounded to the nearest whole frame.
Are the numbers I enter sent to a server?
No. The math runs entirely in your browser, with no external API or data. The frame count, fps, and factors you enter are never uploaded, stored, or sent anywhere — they are processed only on your device.
What is 4n+1 and why is it shown?
Video models like Wan 2.1/2.2 only accept frame counts of a multiple of four plus one (4n+1, e.g. 1, 5, 9 … 81, 121). Other counts may error out or get rounded, so the tool checks whether your value qualifies and, if not, shows the nearest valid frame count above and below — useful for landing on 81 or 121.
What does the interpolation factor change?
Frame interpolation (RIFE and similar) inserts new frames between adjacent ones to raise the frame count. A factor of ×2 makes the interpolated count (original frames − 1) × 2 + 1, and the final fps for smooth playback at the same length becomes the original fps × 2. The length in seconds stays the same.
Can I use it for After Effects or Blender?
Yes. Converting between frames, seconds, and fps is tool-agnostic math, so it works just as well for After Effects compositions, Blender timelines, or matching durations in any video editor. The 4n+1 check is an AI-video helper — for general use you can ignore it and just use the frames/seconds conversion.