How SmoothMotion.video Works
SmoothMotion.video turns your video into a higher frame rate MP4 using motion-compensated interpolation. There is no account and no installation – just a well-understood, predictable processing pipeline. This page walks through exactly what happens to your file from the moment you choose it to the moment it is deleted.
Overview
| Step | What happens |
|---|---|
| 1. Session | An anonymous cookie links your browser to your jobs |
| 2. Upload | Your file is sent to our server |
| 3. Validation | The file is checked for a valid video stream, duration and resolution |
| 4. Queue | The job waits for a free processing slot |
| 5. Processing | New frames are interpolated, encoded and sampled for preview thumbnails |
| 6. Progress | Your browser shows progress and the latest thumbnail |
| 7. Playback and download | You preview and download the MP4 |
| 8. Deletion | All media is deleted 30 minutes after processing finishes |
1. An anonymous session
When you use the tool, your browser receives an anonymous, HTTP-only cookie. It contains no personal information and cannot be read by scripts on the page. Its only job is to link your browser to the jobs you create, so that only you can see their progress, preview the results and download them. There is no sign-up, email address or password.
2. Uploading your video
You choose a file and an output frame rate: 30, 60 (the default) or 120 FPS. Your file must fall within these limits:
- Formats: MP4, MOV, MKV, AVI, WebM, M4V
- Maximum size: 500 MB
- Maximum duration: 5 minutes
- Maximum resolution: 1920×1080
3. Validation
File extensions can be misleading, so once the upload completes the file is checked to confirm it contains a valid video stream. The check reads the container and streams to confirm the video can be decoded and to measure its real duration, resolution and frame rate. Files that are not valid video, or that exceed the limits, are rejected and not processed.
The 30-minute deletion clock described below does not start yet: it starts when processing finishes, so time spent waiting in the queue never eats into your download window.
4. The job queue
Frame interpolation is CPU-intensive, so jobs are not run all at once. Valid uploads join a queue and are picked up by a background worker as soon as capacity is free. While you wait, your browser shows the job's status. You can cancel at any point, which stops the job and deletes its media.
5. Processing
The worker generates new frames using motion-compensated interpolation, raising the video to your chosen frame rate. Motion is estimated bidirectionally between neighbouring frames using a predictive block-based search on 16-pixel blocks. Blocks are subdivided where motion is complex, and new frames are rendered with overlapped block motion compensation to minimise blocky edges. For a full explanation of each stage, see our guide to what motion interpolation is.
The interpolated video stream is then split within the same processing step into two branches:
- The main output, encoded as H.264 video in yuv420p with your original audio encoded as AAC, in an MP4 container with faststart. Your original dimensions are kept and the playback speed is unchanged.
- A thumbnail branch, which periodically writes a small still image from the interpolated frames.
Because the thumbnails come from the same stream as the final video, the preview you see during processing is a genuine sample of your result, not of the original upload.
How long it takes
Motion-compensated interpolation is heavy work and runs on the CPU. Processing can take longer than the video's own duration. Higher resolutions and 120 FPS output take the longest, because there are more pixels to analyse and more frames to generate and encode.
6. Live progress
While processing runs, the server tracks how far through the video it has got. Your browser checks in regularly and updates the progress bar along with the most recent thumbnail. If something looks wrong in the preview, you can cancel early rather than waiting for the whole job.
7. Preview and download
When processing finishes, the result can be played directly in your browser. Thanks to faststart, playback begins without downloading the whole file first. The download is named after your original, for example holiday_smoothmotion_60fps.mp4. The file is a standard MP4 that works in browsers, on phones and in video editors.
8. Automatic deletion
All uploaded and processed media – your original file, the interpolated video and the thumbnails – is deleted automatically 30 minutes after processing finishes. Viewing or downloading the result does not extend this window, so download your video promptly. If a video cannot be processed within 3 hours of upload – for example because the queue is unusually busy – it is deleted as well. Deleted files cannot be recovered.
Separately, basic job metadata – such as the file name, file sizes, chosen settings and timings, but no media – is kept for up to 24 hours for operational purposes. After that it is deleted or folded into anonymous aggregate statistics. Full details are in our privacy policy.
Why it is built this way
- Well-understood techniques. Motion-compensated interpolation is mature and transparent, and the approach used is described above.
- Predictable output. A single, compatible MP4 format means the result plays almost everywhere.
- Minimal data. No accounts, short retention and no stored media beyond 30 minutes.
To learn about the technique itself, read our introduction to video frame interpolation. If you have questions this page does not answer, try the FAQ or start smoothing a video on the home page.