How to slow down action-cam footage to 1/4 speed
- Step 1Drop in the action-cam clip — Accepts MP4, MOV, MKV, WebM, AVI, M4V, TS — covering GoPro MP4, DJI MP4/MOV, and Insta360 exports. The file is read locally; nothing uploads. Slow-mo requires a Pro subscription (£7/month). The file card shows duration and resolution.
- Step 2Check your source frame rate first — Smoothness depends on the source fps, not this tool. 120 fps slowed to 0.25× plays back like a clean 30 fps slow-mo. 30 fps slowed to 0.25× shows each frame four times longer and looks choppy. If smoothness matters, re-shoot at a higher frame rate — this tool can't add frames.
- Step 3Set Speed to your slow-mo target — Type
0.25for the maximum stretch,0.5for a tasteful half-speed, or anything between in the Speed (× · 0.25 to 4) field. Below0.25is rejected. Output duration ≈ input ÷ speed, so 0.25× makes the clip four times longer. - Step 4Run the slow-down — Click Run Speed. FFmpeg builds
[0:v]setpts=4.0000*PTS[v];[0:a]atempo=0.5,atempo=0.5[a]for 0.25×, re-encoding to H.264 CRF 20 + AAC 192k. The dashboard shows progress; large 4K files take longer in the browser. - Step 5Download the slow-mo MP4 — The result is a standard
.mp4you download (this tool doesn't stream to disk). Review the motion: if it stutters, the source frame rate was the limit, not the speed value. - Step 6Trim to the action beat first — You rarely want the whole clip in slow-mo. Cut to just the jump/wave/reveal with the lossless trimmer before slowing down — it keeps the export fast and the slow-mo focused. For a reverse-slow-mo replay effect, see the video reverser.
Source frame rate vs. effective slow-mo smoothness
This tool conforms existing frames; it does not interpolate. Effective fps after slow-down = source fps × speed. Below ~24 fps effective, motion looks choppy.
| Source fps | At 0.5× | At 0.25× | Smoothness at 0.25× |
|---|---|---|---|
| 240 fps (GoPro) | 120 fps eff. | 60 fps eff. | Very smooth |
| 120 fps (GoPro/DJI) | 60 fps eff. | 30 fps eff. | Smooth |
| 60 fps (drone/phone) | 30 fps eff. | 15 fps eff. | Slightly choppy |
| 30 fps (standard) | 15 fps eff. | 7.5 fps eff. | Choppy — re-shoot higher |
| 24 fps (cinematic) | 12 fps eff. | 6 fps eff. | Very choppy |
Slow-mo speed values and the filters built
How each slow-down value maps to setpts and atempo. atempo chains below 0.5 because a single instance can't go under 0.5.
| Speed | setpts (video) | atempo (audio) | Duration (10s clip) |
|---|---|---|---|
0.75 | 1.3333*PTS | atempo=0.7500 | 13.3 s |
0.5 | 2.0000*PTS | atempo=0.5000 | 20 s |
0.4 | 2.5000*PTS | atempo=0.5,atempo=0.8 | 25 s |
0.3 | 3.3333*PTS | atempo=0.5,atempo=0.6 | 33.3 s |
0.25 | 4.0000*PTS | atempo=0.5,atempo=0.5 | 40 s (max stretch) |
Cookbook
Slow-motion recipes for GoPro, DJI, and Insta360 footage — and how to avoid stuttery results.
GoPro 120 fps jump to clean 0.25× slow-mo
High-frame-rate source is the right way to do dramatic slow motion. 120 fps at 0.25× lands at an effective 30 fps — smooth playback, four times longer.
Source: GoPro 120 fps, 5 s clip Speed field: 0.25 [0:v]setpts=4.0000*PTS[v];[0:a]atempo=0.5,atempo=0.5[a] 5 s -> 20 s output, ~30 fps effective, smooth
Why a 30 fps clip stutters at 0.25×
Standard 30 fps footage has no spare frames. Stretched 4×, each frame shows ~4× longer and motion looks like a slideshow. There's no interpolation here to smooth it.
Source: phone 30 fps, 5 s clip Speed field: 0.25 Effective fps: 30 x 0.25 = 7.5 fps -> choppy Fix: re-shoot at 120/240 fps, or use 0.5x (15 fps) instead
Tasteful half-speed for a drone reveal
For 60 fps drone footage, 0.5× gives a graceful slow reveal at an effective 30 fps without going to the choppy extreme.
Source: DJI 60 fps reveal Speed field: 0.5 [0:v]setpts=2.0000*PTS[v];[0:a]atempo=0.5000[a] 8 s -> 16 s, 30 fps effective, audio pitch intact
Trim to the beat, then slow it
Slow-mo the action, not the whole clip. Cut to the 3-second jump first, then stretch — keeps the export fast and the result punchy.
Step 1: lossless-trimmer -> isolate the 3 s jump
Step 2: speed-controller, Speed 0.25
3 s -> 12 s dramatic slow-mo
Faster to process than slowing the full 2-min clip.Slow value below the floor is rejected
0.25× is the slowest this tool goes. Anything below errors out rather than producing a file.
Speed field: 0.1 Result: Error: Speed must be between 0.25x and 4x. Fix: use 0.25 (max stretch). For more, run the 0.25x output through again (0.25 x 0.25 = 0.0625x effective).
Edge cases and what actually happens
Stuttery slow-mo from a 30 fps source
By designThis tool conforms existing frames; it does not interpolate. A 30 fps clip at 0.25× plays at an effective 7.5 fps and looks choppy. The only real fix is a higher-frame-rate source. As a compromise, 0.5× on 30 fps (15 fps effective) is far less choppy than 0.25×.
Speed below 0.25
Rejected (error)0.25× is the floor. Values under it return Speed must be between 0.25× and 4×. and nothing is processed. For more extreme slow-down, run the 0.25× export back through the tool — the factors multiply (0.25 × 0.25 = 0.0625× effective), though stutter compounds too.
Action clip recorded without audio
FailsSome action-cam modes (or wind-noise-muted exports that strip the track entirely) have no audio stream. The filter graph always maps [0:a] through atempo, so a track-less file fails. Keep an audio track on the clip, or add a silent one in another tool before slowing down.
HEVC / H.265 GoPro or DJI source
SupportedHEVC source decodes fine in WebAssembly FFmpeg, and the output is always H.264 MP4 — which is convenient because H.264 plays in editors that struggle with HEVC. The re-encode to H.264 CRF 20 is the trade-off for that compatibility.
Audio at 0.25× sounds slightly smeared
Expected0.25× audio is a chained atempo=0.5,atempo=0.5, stretching the waveform 4×. At that extreme, wind, music, or speech can sound mildly smeared. Pitch is still preserved (no rumble) — the smearing is inherent to heavy time-stretching, not a defect.
Large 4K HEVC file is slow to process
May be slow4K HEVC decode plus H.264 re-encode in the browser is heavy. Within your tier's file-size limit it works, but expect a wait and high RAM. Trim to just the action beat first to keep it quick — you almost never want a whole 4K clip in slow motion anyway.
Variable-frame-rate phone slow-mo files
SupportedSome phones store 'slo-mo' as a VFR file with a high capture rate. setpts re-times by timestamp and the export is re-encoded, so these conform correctly. The effective smoothness still depends on the actual captured frame rate inside the file.
Output container is MP4, not the original MOV
By designDJI/GoPro MOV inputs come back as H.264 MP4. That's the universal-compatibility default. If you specifically need MOV (e.g. for a Final Cut workflow), run the MP4 through the transcoder.
Free tier — slow-mo gated
Pro requiredSlowing video down requires Pro (£7/month). File-size limits: Free 1 GB / 1 file, Pro 10 GB / 5 files, Pro + Media 100 GB / 50 files. There's no duration cap — only size and batch count constrain the job.
Batch of clips at one slow-mo speed
Supported (batch)Drop several action clips together to queue a batch (5 on Pro, 50 on Pro + Media). The same Speed applies to all — useful for slowing every clip in a montage to the same 0.5× before editing.
Frequently asked questions
How slow can I go?
0.25× is the floor, which stretches the clip to four times its original length. Values below 0.25 are rejected. For more extreme slow motion, run the 0.25× output through the tool a second time — the factors multiply — but be aware stutter compounds on low-frame-rate sources.
Why does my slow motion look choppy?
Because the tool stretches the frames you already captured rather than generating new ones. A 30 fps clip at 0.25× plays at an effective 7.5 fps, which stutters. For smooth slow-mo, shoot at a high frame rate (120 or 240 fps) so there are enough frames to stretch.
Does the audio drop into a low rumble when I slow down?
No. The audio is time-stretched with atempo, which keeps the original pitch. Even at 0.25× (built as a chained atempo=0.5,atempo=0.5), the sound just plays slower at the same pitch rather than dropping in tone.
Will it add frames for smoother slow-mo?
No — there is no frame interpolation in this tool. It conforms existing frames over a longer time. Smoothness comes entirely from the source frame rate. If you need synthesised in-between frames, that's a different kind of tool than this one.
Can I slow down GoPro HEVC / H.265 footage?
Yes. HEVC source decodes in the browser, and the output is always H.264 MP4 — which actually helps, since H.264 plays in editors that struggle with HEVC. The cost is a re-encode to H.264 at CRF 20.
Is my big action-cam file uploaded?
No. Processing runs in your browser with WebAssembly FFmpeg, so multi-gigabyte GoPro/DJI files stay on your machine and never upload. Only an anonymous 'file processed' counter is logged for dashboard stats.
What's the output format?
A standard H.264 MP4 (CRF 20) with AAC audio, regardless of whether the source was MP4, MOV, or HEVC. If you need MOV for Final Cut or another container, run the MP4 through the transcoder afterwards.
Should I trim before slowing down?
Yes — slow-mo the action beat, not the whole clip. Cut to the jump, wave, or reveal with the lossless trimmer first. It keeps the export fast and the slow-motion focused on the moment that matters.
My clip has no audio and won't process — why?
The filter graph always routes an audio stream through atempo. If the clip has no audio track at all, the job fails with a mapping error. Keep an audio track on the file, or add a silent one in another tool before slowing it down.
Can I slow several clips at once?
Yes. Dropping multiple files queues a batch — up to 5 on Pro or 50 on Pro + Media — and the same Speed is applied to each. That's handy for taking every clip in a montage down to a consistent 0.5× before you edit.
How big a file can I slow down?
Free allows up to 1 GB / one file, Pro up to 10 GB / five files, Pro + Media up to 100 GB / fifty files. There's no minutes cap — only file size and batch count. Slow-motion itself requires the Pro tier (£7/month).
Can I make a reverse slow-motion replay?
Slow it here, then reverse it with the video reverser (or reverse first, then slow). This tool only changes speed; it doesn't reverse playback, so the replay effect is a two-tool combination.
Privacy first
Every JAD Video tool runs entirely in your browser via WebCodecs and FFmpeg (WebAssembly). Your video files never leave your device — verified by zero outbound network requests during processing.