Fast trim uses the compatible local path
Fast trim lets the local engine use compatible conversion optimizations. This first writer does not promise keyframe-aligned or lossless trimming; the result is remeasured before it is offered for download.
Local video trimmer
Trim or cut a video by time
Set a start and end for one local clip. Fast trim uses the compatible local path when possible; Exact trim is for frame-oriented boundaries when local re-encoding is supported.
Your video stays on this device. No upload, account, or server-side processing job.
Browser-local workspace
Choose a local video to begin.
Choose one local MP4, M4V, MOV, or WebM file. JavaScript activates a browser-native preview and capability check; available conversions depend on the codecs supported by this device.
No upload, account, or server-side media job.
The local workspace loads after you choose a video.
Exact trim trades speed for the boundary
An exact boundary requires a local decode and re-encode of the kept section. The workspace makes that cost visible before starting, especially for high-resolution or long sources.
Private browser processing
Your video remains in your hands.
Aftermath reads selected video bytes only in the current browser. Unsupported codecs are reported clearly rather than sent to another service. High-resolution conversion can use substantial device battery and processing.
Try a measured example
A one-second cut, checked after export
We requested the first second of this recording using Fast trim. The downloaded result was reopened and measured.
- Choose a video and set the start and end.
- Create the result and check its measured duration.
- Download it, or choose a next step beside the result.
| Before trimming · WebM | Bytes: 32,627 Seconds: 1.804 Pixels: 640 × 360 |
|---|---|
| After trimming · MP4 | Bytes: 17,835 Seconds: 1.012 Pixels: 640 × 360 |
Fast trim can follow encoded packet boundaries. Use Exact when the cut point matters. Fast trimming can also retain the source codec inside an MP4 container.
Play the sample clips
Tested: · Chromium 149.0.7827.55
How we checked
These files passed through the actual tool controls. Downloads were reopened to check sizes, duration, dimensions, or page structure. Capture used synthetic streams; hardware permissions were not tested.
These synthetic samples are free to reuse under CC0. No personal files or recordings were used. Your results may differ.
How to use this tool
Trim a local MP4, M4V, MOV, or WebM video to one chosen start-to-end range. Fast mode uses a compatible local path when a nearby boundary is acceptable; Exact mode requests frame-oriented re-encoding when supported. The separate result is reopened and measured before download. This browser workflow does not join clips, add effects, or promise a lossless or keyframe-exact cut. One completed output is limited to 500 MB in browser memory.
What to choose and what you get
What to choose
- one selected local MP4, M4V, MOV, or WebM file
Result
- a separately downloaded video containing the selected kept time range
Supported use
- One readable local video with a measurable duration and a valid start and end selection.
- Fast mode when compatible local optimizations and a nearby cut boundary are acceptable.
- Exact mode when the visual boundary matters and the browser supports the required decode and encode path.
Before you start
- Multi-clip assembly, transitions, effects, captions, or a general editing timeline.
- A guarantee that Fast trim copies packets losslessly or lands on an exact requested frame.
Supported formats
- Accepted formats: MP4, M4V, MOV, WebM.
- Output formats: MP4.
Browser support and permissions
- Modern browser with JavaScript and support for the selected media container and codec; memory and performance vary by device. Output operations keep one completed result in browser memory and are limited to 500 MB; read-only inspection can handle larger accepted sources up to 4 GB.
- No camera, microphone, or screen permission is needed.
Choose the right settings
- Use Fast when a compatible local path and nearby boundary are acceptable; use Exact when frame-oriented boundaries matter.
- Use /video/compress when size is the goal without removing time, or /video/crop when framing is the goal.
- Use /audio-cutter for an audio-only source and /video when the broader operation is undecided.
- Review the separately written clip before replacing the source.
Worked example
A 90-second clip should keep only 12.5–38.0 seconds, with exact timing preferred over the compatible fast path.
Starting facts
- The keep range is explicit and within source duration.
- Exact trimming can require local decoding and re-encoding.
Observed operation: Set the range, choose the timing mode and create a separate video containing only the selected interval.
Review the result: Check the first and last frames, output duration, audio sync and playback across the entire result.
Boundary: Fast trimming may follow media boundaries, while exact trimming can change encoding quality and unsupported tracks.
What you can do
Keep one chosen time range from a local video using the compatible fast path or an exact re-encode
Choose another tool when
- Reducing byte size without selecting a time range belongs to /video/compress.
- Changing the frame or aspect ratio belongs to /video/crop.
- This route does not join clips, build a timeline, or promise that Fast trim is keyframe-aligned or lossless.
If it does not work
- A source without a readable duration cannot expose a valid kept-range control.
- An empty, reversed, or otherwise invalid range is rejected before processing.
- Exact mode or an incompatible fast path fails locally when the required source decoder or output encoder is unavailable.
Things to know
- Codec support, performance, and memory use vary by browser, device, source, and operation.
Privacy boundary
The selected video stays in the current browser session and is not sent to an Aftermath processing service. How local processing is verified.
What this tool verifies
Checks the displayed limits and reports or creates a separately downloaded video containing the selected kept time range from one selected local MP4, M4V, MOV, or WebM file.
Check before sharing
Reducing byte size without selecting a time range belongs to /video/compress.