Changing video speed without changing the pitch? These 2 parameters matter
A tutorial that wants 1.5x, sports footage that wants slow motion, and the voice turns shrill or muffled after a speed change? setpts and atempo have to be paired.
Recording a course, I often think there is too much filler and want to post it at 1.5x; shooting a product, I need 0.5x slow motion to look at the detail — after a simple speed-up, voices sound like a cartoon squirrel and the background music turns muffled. Changing the video speed without changing the pitch relies on two ffmpeg concepts: setpts changes the speed of the picture, atempo changes the audio while keeping its pitch.
What setpts + atempo are
setpts (video)
Adjusts the presentation timestamp. For example setpts=0.5*PTS makes the picture play at 2x (the timestamps are compressed to half). A value below 1 speeds it up, above 1 slows it down.
atempo (audio)
Changes the playback speed while keeping the pitch. ffmpeg's atempo handles 0.5–2.0x in one go; beyond that you have to chain filters (4x = 2.0 × 2.0).
The two have to stay in sync: at 2x for the picture, the audio needs atempo=2.0 as well, otherwise the sound drifts or the pitch changes.
TwoThink Change Video Speed sets up that filter pair for you in the browser — pick 0.5x / 1.25x / 1.5x / 2x and you do not have to remember the commands.
Real scenarios
A tutorial at 1.5x
A 20-minute original becomes about 13 minutes, the voice stays clear and intelligible, and viewers save time. Do not go past 2x or the words stop being easy to follow.
Sports footage at 0.5x
You can see the movement in detail; combine it with Trim Video to slow down only the key three seconds instead of the whole clip, which keeps the pace from dragging.
Speeding up the whole video, then compressing to publish
The bitrate distribution changes after a speed change, so run Compress Video before uploading to keep the size under control.
| Rate | Picture | Audio | Good for |
|---|---|---|---|
| 0.5x | slow motion | pitch kept | sports / product shots |
| 1.25x | slightly faster | pitch kept | light editing |
| 1.5x | a tutorial staple | pitch kept | explainers |
| 2x | quick review | pitch kept | recaps / jokes |
Pitfalls
- Only the video is changed, not the audio: the classic squirrel voice.
- Going past 2x with a single atempo: it errors out or changes the pitch — chain the filters.
- Music mixed with narration: atempo applies to the whole track, so the music speeds up too; to speed up only the narration you have to split the tracks first with Extract Audio (advanced).
- Vertical footage: changing the speed does not change the aspect ratio, so landscape footage for TikTok should still go through Landscape to Vertical Video first.
My advice
For explainer videos: rough cut → Change Video Speed at 1.25–1.5x → Watermark Video → Compress Video before publishing. It gives viewers a better default experience than leaving them to press "play at 1.5x" themselves.
Try it → Open Change Video Speed, try 1.5x on thirty seconds of narration and listen to whether the voice still sounds normal.