Keep the transform intentional
A single video transform applies rotation, crop, resize, optional background, and encode once. Repeated full-resolution canvas passes waste memory and can soften the image unnecessarily.
Local video crop and resize
Frame a video for its destination in one deliberate pass.
Choose Original, 16:9, 9:16, 1:1, 4:5, Custom, or an App Store starting point. Then decide whether to crop, fit with a background, or use a blurred background when local encoding is available.
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.
Choose what happens to the edges
Crop to fill removes outer content to fill the target frame. Fit with a background keeps the full source visible. A blurred background can soften the unused space without pretending the frame was originally captured that way.
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.
How to use this tool
Use this route when a local video needs a different frame rather than a shorter duration or smaller byte target. Choose a standard, custom, or App Store-oriented aspect ratio, then crop to fill, fit with a background, or use blurred fill. The browser previews retained edges and planned dimensions, performs one supported local transform, and reopens the separate MP4 result before download.
What to choose and what you get
What to choose
- one selected local MP4, M4V, MOV, or WebM file
Result
- a separately downloaded MP4 with the selected frame and fit treatment
Supported use
- Original, 16:9, 9:16, 1:1, 4:5, custom, and App Store-oriented frame choices for one readable video.
- Crop-to-fill, full-frame fit, or blurred-background treatment with a visible retained-area and padding preflight.
- A one-pass local rotation, crop, resize, fit, and MP4 encode when the required browser capabilities are present.
Before you start
- Timeline edits, multi-layer composition, arbitrary effects, or certification against a destination’s submission policy.
- Silent substitution of a different fit treatment when OffscreenCanvas or a required local codec is unavailable.
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 Crop to fill when losing outer content is acceptable; use Fit or Blurred when every source edge must remain visible.
- Use /video/trim for time boundaries, /video/compress for a byte goal, or /video/app-store-preview for the separate submission-oriented checklist.
- Use /video when the intended operation is still broad.
- Review the preflight and reopened output because enlargement or edge removal can change the result materially.
Worked example
A landscape clip needs a vertical 9:16 frame with the speaker kept inside the crop throughout the segment.
Starting facts
- The intended output frame and fit method are explicit.
- A fixed crop cannot track a moving subject automatically.
Observed operation: Choose the 9:16 frame, set crop or fit placement and encode the supported video locally into a separate MP4.
Review the result: Play the whole output and inspect subject framing, padding, dimensions, audio sync and rotation.
Boundary: The route does not perform motion tracking, editorial reframing or guarantee codec and platform acceptance.
What you can do
Crop, fit, or resize one local video into a chosen aspect ratio and output frame
Choose another tool when
- Shortening duration belongs to /video/trim, and reducing bytes without reframing belongs to /video/compress.
- The App Store preset here is a framing starting point, not App Store technical validation or approval.
- This route does not offer a multi-layer editor, effects timeline, or server rendering fallback.
If it does not work
- Unreadable source dimensions prevent a trustworthy crop, padding, scale, and output-size preflight.
- Invalid custom dimensions or an unavailable OffscreenCanvas block the requested custom or blurred treatment.
- The local transform stops when source decoding, MP4 encoding, memory bounds, or output validation cannot be satisfied.
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 MP4 with the selected frame and fit treatment from one selected local MP4, M4V, MOV, or WebM file.
Check before sharing
Shortening duration belongs to /video/trim, and reducing bytes without reframing belongs to /video/compress.