48 kHz
job_a6d9228854f0405aThe video-standard rate.
ffmpeg -i https://cdn.rendobar.com/assets/examples/sample.mp4 -af "aresample=48000" -c:v copy -t 5 out.mp4audio filter
The FFmpeg aresample filter
Converts audio sample rate, and can compensate for timestamp drift.
3 of 3 variants measured Measured 2026-08-20
The part that catches people
aresample=async=1 is the fix for audio that slowly desynchronises from video, because it inserts or drops samples to follow the timestamps. Plain rate conversion will not fix drift, and drift is usually why someone reached for this filter.
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 |
|---|---|---|---|
| 48 kHz | 155 ms | 363.5 KB · 1280x720 | $0.0015 |
| 44.1 kHz | 152 ms | 363.9 KB · 1280x720 | $0.0016 |
| Drift compensation | 151 ms | 363.5 KB · 1280x720 | $0.0017 |
The fastest variant here is not the smallest. Drift compensation finished the encode in 151 ms, while 48 kHz produced the smallest file at 363.5 KB. Which one matters depends on whether you are paying for compute or for storage.
The exact commands
44.1 kHz
job_0a35a041eedf4832The CD-audio rate, still common in music sources.
ffmpeg -i https://cdn.rendobar.com/assets/examples/sample.mp4 -af "aresample=44100" -c:v copy -t 5 out.mp4Drift compensation
job_214a7fd54d234fb5The desync fix, not a rate change.
ffmpeg -i https://cdn.rendobar.com/assets/examples/sample.mp4 -af "aresample=async=1:first_pts=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 aresample filter do?
Converts audio sample rate, and can compensate for timestamp drift.
What is the most common mistake with aresample?
aresample=async=1 is the fix for audio that slowly desynchronises from video, because it inserts or drops samples to follow the timestamps. Plain rate conversion will not fix drift, and drift is usually why someone reached for this filter.
How long does aresample take to run?
On a 1280x720 five-second H.264 source, the fastest variant on this page (Drift compensation) spent 151 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 aresample?
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. atempo Changes audio playback speed without changing pitch. volume Scales audio gain by a ratio or in decibels. afade Fades audio in or out over a duration, with selectable curve. silenceremove Strips silent passages from audio, by threshold and minimum duration.
Run aresample without installing FFmpeg
Every command on this page ran through the API against a URL. No binary, no server.