2x faster
job_22571583f69e4332Halve the timestamps to double the speed.
ffmpeg -i https://cdn.rendobar.com/assets/examples/sample.mp4 -vf "setpts=0.5*PTS" -t 5 out.mp4video filter
The FFmpeg setpts filter
Rewrites presentation timestamps, which is how video speed is changed.
3 of 3 variants measured Measured 2026-08-20
The part that catches people
setpts changes video speed and does nothing to audio, so speeding up video alone desynchronises the sound. The audio side needs atempo with the reciprocal factor, and the two numbers are inverses of each other, which is a common off-by-inversion bug.
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 |
|---|---|---|---|
| 2x faster | 735 ms | 453.0 KB · 1280x720 | $0.0021 |
| Half speed | 650 ms | 288.1 KB · 1280x720 | $0.0020 |
| Rebase to zero | 939 ms | 514.0 KB · 1280x720 | $0.0023 |
The exact commands
Half speed
job_e61dcf5da1744157Double the timestamps to halve the speed.
ffmpeg -i https://cdn.rendobar.com/assets/examples/sample.mp4 -vf "setpts=2.0*PTS" -t 5 out.mp4Rebase to zero
job_b419d4c413314625No speed change. The companion to trim.
ffmpeg -i https://cdn.rendobar.com/assets/examples/sample.mp4 -vf "setpts=PTS-STARTPTS" -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 setpts filter do?
Rewrites presentation timestamps, which is how video speed is changed.
What is the most common mistake with setpts?
setpts changes video speed and does nothing to audio, so speeding up video alone desynchronises the sound. The audio side needs atempo with the reciprocal factor, and the two numbers are inverses of each other, which is a common off-by-inversion bug.
How long does setpts take to run?
On a 1280x720 five-second H.264 source, the fastest variant on this page (Half speed) spent 650 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 setpts?
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. fps Resamples video to a constant frame rate by duplicating or dropping frames. 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.
Run setpts without installing FFmpeg
Every command on this page ran through the API against a URL. No binary, no server.