1.5x faster
job_a89ccc71ce044f26Inside the single-instance range.
ffmpeg -i https://cdn.rendobar.com/assets/examples/sample.mp4 -af "atempo=1.5" -c:v copy -t 5 out.mp4audio filter
The FFmpeg atempo filter
Changes audio playback speed without changing pitch.
3 of 3 variants measured Measured 2026-08-20
The part that catches people
atempo only accepts 0.5 to 2.0 in a single instance. Anything outside that has to be chained, so 4x is atempo=2.0,atempo=2.0. Passing 4.0 directly is an error, not a clamp.
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 |
|---|---|---|---|
| 1.5x faster | 123 ms | 337.0 KB · 1280x720 | $0.0015 |
| Half speed | 150 ms | 363.5 KB · 1280x720 | $0.0015 |
| 4x, chained | 80 ms | 303.6 KB · 1280x720 | $0.0017 |
The exact commands
Half speed
job_b8baad56f18e47abThe bottom of the range.
ffmpeg -i https://cdn.rendobar.com/assets/examples/sample.mp4 -af "atempo=0.5" -c:v copy -t 5 out.mp44x, chained
job_11663a97bdba4012The only way past 2.0.
ffmpeg -i https://cdn.rendobar.com/assets/examples/sample.mp4 -af "atempo=2.0,atempo=2.0" -c:v copy -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 atempo filter do?
Changes audio playback speed without changing pitch.
What is the most common mistake with atempo?
atempo only accepts 0.5 to 2.0 in a single instance. Anything outside that has to be chained, so 4x is atempo=2.0,atempo=2.0. Passing 4.0 directly is an error, not a clamp.
How long does atempo take to run?
On a 1280x720 five-second H.264 source, the fastest variant on this page (4x, chained) spent 80 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 atempo?
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
loudnorm Normalises perceived loudness to a target LUFS, following EBU R128. volume Scales audio gain by a ratio or in decibels. afade Fades audio in or out over a duration, with selectable curve. aresample Converts audio sample rate, and can compensate for timestamp drift. silenceremove Strips silent passages from audio, by threshold and minimum duration.
Run atempo without installing FFmpeg
Every command on this page ran through the API against a URL. No binary, no server.