Frame Rate Conversion Calculator
When post-production requires video to be delivered at a different frame rate than it was shot, the conversion method matters. A simple conform (reinterpret, no new frames) changes playback speed and audio pitch. A true frame-rate conversion inserts or removes frames to keep the duration the same. This calculator shows the conform speed ratio, the resulting audio pitch change, and the corrected clip duration after a simple conform.
Conform ratio formula
Speed ratio = target fps / source fps
New duration (s) = original duration x (source fps / target fps)
Pitch shift (semitones) = 12 x log2(target fps / source fps)
Example: 24 fps source, 25 fps target. Speed ratio = 25/24 = 1.042 (4.2% faster). 60-second clip becomes 60 x (24/25) = 57.6 seconds. Pitch shift = 12 x log2(25/24) = 0.71 semitones higher.
Common frame rate conversions
- 24 fps to 25 fps (film to PAL): 4.2% speed increase, 0.71 semitone pitch rise. Classic European broadcast conform.
- 23.976 fps to 29.97 fps: ratio 1.25x (telecine with pulldown adds frames).
- 25 fps to 29.97 fps: ratio 1.199x conform, or full conversion using frame interpolation.
- 60 fps to 24 fps: often used intentionally for 2.5x slow-motion playback.
Frame rate conversion: frequently asked questions
What is frame rate conversion?
Frame rate conversion changes a video from one frame rate to another. There are two approaches: conform (interpret the source frame rate as the target without adding or removing frames, which changes playback speed) or pulldown (add or remove frames to change the timeline duration while keeping speed the same).
What is the 24p to 25p conform process?
Conforming 24 fps content to 25 fps means playing each frame at 25 fps instead of 24 fps. This speeds up the video by 25/24 = 1.042x and raises the audio pitch by about 0.7 semitones. This was the standard conversion for film to PAL broadcast television.
How does 3:2 pulldown convert 24 fps to 30 fps?
3:2 pulldown (telecine) distributes 24 film frames into 30 video frames by repeating fields. Every 4 film frames become 5 video frames (two frames hold 3 fields, two hold 2 fields). This is how 24 fps film was broadcast on NTSC (29.97 fps) television.
What happens to audio pitch when conforming frame rates?
When you conform (speed up or slow down without resampling), pitch changes proportionally. Pitch change in semitones = 12 x log2(target fps / source fps). A 24-to-25 conform shifts pitch by 12 x log2(25/24) = about 0.71 semitones higher.
How do I avoid the speed and pitch change when converting frame rates?
Use a retiming (motion-blur frame interpolation) workflow in software like DaVinci Resolve or After Effects. Optical flow retiming creates new intermediate frames and uses time-stretching on audio, preserving both speed and pitch at the cost of some motion artifacts.
Official sources
- SMPTE ST 12-1: Time and Control Code (frame rate standards). SMPTE.org.
- ITU-R BT.709: Parameter values for HDTV standards (frame rate specifications). ITU.int.
Reviewed by the CalculatorHub team, edited by James Graham, 15 June 2026. See our methodology.