30 fps
job_6b53f34fb6bb4333The common normalisation target.
ffmpeg -i https://cdn.rendobar.com/assets/examples/sample.mp4 -vf "fps=30" -t 5 out.mp4video filter
The FFmpeg fps filter
Resamples video to a constant frame rate by duplicating or dropping frames.
3 of 3 variants measured Measured 2026-08-20
The part that catches people
fps is a filter and -r is an output option, and they are not the same thing. -r can change timestamps without touching frames; fps actually duplicates and drops so the output is genuinely constant-rate. Mixing both is how you get doubled durations.
Measured, not described
Every row below is a real job. The same 1280x720 five-second H.264 source went through each variant, so the numbers are comparable to each other and to every other filter page on this site. Encode time is the FFmpeg step on its own, separated from the download and the upload.
| Variant | Encode | Output | Cost |
|---|---|---|---|
| 30 fps | 4034 ms | 627.1 KB · 1280x720 | $0.0056 |
| 15 fps | 2620 ms | 612.2 KB · 1280x720 | $0.0042 |
| Film rate | 1167 ms | 513.8 KB · 1280x720 | $0.0044 |
The exact commands
15 fps
job_a97e6778d5b64bf8Halved rate, to show the effect on output size.
ffmpeg -i https://cdn.rendobar.com/assets/examples/sample.mp4 -vf "fps=15" -t 5 out.mp4Film rate
job_92621424f0cb4bcaExact 23.976 as a fraction. Writing 23.976 introduces drift over long files.
ffmpeg -i https://cdn.rendobar.com/assets/examples/sample.mp4 -vf "fps=24000/1001" -t 5 out.mp4How these numbers were produced
Each variant was submitted to the Rendobar API as an ffmpeg job against the same public source file, and the response was recorded verbatim. Encode time is the API's own per-step timing for the FFmpeg step. Output size is the byte count of the file the job produced. Cost is what the job was actually billed.
Nothing here was estimated, and the whole set is re-runnable, so if a figure looks wrong it can be checked rather than argued about. The 72 variants behind this filter reference cost $0.193082 in total to measure.
Frequently asked questions
What does the FFmpeg fps filter do?
Resamples video to a constant frame rate by duplicating or dropping frames.
What is the most common mistake with fps?
fps is a filter and -r is an output option, and they are not the same thing. -r can change timestamps without touching frames; fps actually duplicates and drops so the output is genuinely constant-rate. Mixing both is how you get doubled durations.
How long does fps take to run?
On a 1280x720 five-second H.264 source, the fastest variant on this page (Film rate) spent 1167 ms inside FFmpeg. That figure is the encode step alone, measured separately from the download and the upload, so it is the filter's own cost rather than the round trip.
Do I need FFmpeg installed to use fps?
Not with Rendobar. Every command on this page ran through the Rendobar API against a URL, with no local FFmpeg install and no server. The job id next to each row is the real job that produced the numbers.
Other filters, measured the same way
scale Resizes video to a target width and height, with optional aspect-preserving arithmetic. crop Cuts a rectangle out of each frame, positioned from the top-left corner. transpose Rotates video by 90 degree steps, optionally flipping as it goes. pad Adds bars around the frame to reach a target size without cropping the picture. overlay Composites one video or image on top of another at a chosen position.
Run fps without installing FFmpeg
Every command on this page ran through the API against a URL. No binary, no server.