Video Speed Ramp Editor
Set speed keyframes along source time and the tool linearly interpolates speed between them. It integrates 1/speed to calculate the output duration, inverts that clock for each output frame, and encodes a new playable video. Unlike trimming a segment or synthesizing intermediate motion, this changes the playback clock across the entire clip. A CSV/JSON map shows both requested source time and the decoded source frame actually used.
Key features
- Place up to eight speed points from 0.25× to 4× and interpolate smoothly in source time
- Use an exact per-segment time integral, including slowdown and speedup transitions
- Export a playable MP4 or WebM with output times mapped to source-frame times
- Download requested and actually decoded source times for every output frame as CSV and JSON
- Preview source and result, with clear local file, duration, codec and output limits
How to use
- Select a 0.5–12-second MP4/WebM file or create the moving four-second sample.
- Adjust each speed point; add a point to the largest source-time gap or remove an interior point.
- Review the calculated output length and encode the ramped video.
- Play the source and result, then download the video and CSV/JSON time map.
Use cases
- Ease into slow motion for a short product reveal
- Accelerate setup and slow down the important moment in a demo clip
- Check exact timing before cutting against a separately edited sound track
- Save an auditable source/output time map for a video workflow
Frequently asked questions
Is a speed ramp different from trimming?
Yes. Trimming selects a shorter source range. This editor keeps the full short clip and changes the source-to-output clock continuously using speed points.
How is output duration computed?
Between two points speed is linear in source time. Output time is the integral of 1 divided by that speed, calculated analytically for each segment rather than estimated from the number of output frames.
Can I freeze or reverse the clip?
No. Every speed must be between 0.25× and 4×. Zero, negative and nonfinite speeds are rejected because they cannot make a finite forward time map.
Is sound stretched with the picture?
No. Output is silent. Pitch-preserving audio retiming, captions and metadata are outside this tool; download the time map if a separate sound workflow needs the new clock.
Will fast motion become smooth slow motion?
No new motion is synthesized. A fixed output frame cadence samples the existing decoded pictures, so slow sections can repeat source frames and fast sections can skip some. Use frame interpolation separately if needed.
Which formats and limits apply?
Input must be a browser-decodable MP4/WebM of 0.5–12 seconds and at most 48 MiB. The output is at most 30 seconds, 480 pixels on the long edge and 48 MiB. The browser chooses AVC/MP4 or VP8/WebM support.
Privacy
The video and generated files stay in this browser and are not uploaded by this tool. Processing uses the browser's local video decoder and encoder. The result is silent: source audio, captions and metadata are not retimed or copied.
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