Skip to content
Lizely

Video Cropper

Crop a browser-decodable video to an exact in-frame pixel rectangle and download a finite-duration WebM without uploading it.

Privacy: your files never leave your device. All processing happens locally in your browser.

How to use

  1. 1.Choose a browser-decodable video and wait for its source dimensions to load.
  2. 2.Enter whole-pixel X, Y, width, and height values that stay inside every source frame.
  3. 3.Select Crop video, keep the tab open during real-time processing, then download and fully review the WebM.

About Video Cropper

Video Cropper removes the outer area of one browser-decodable video by re-recording an exact rectangular region. Choose an MP4, WebM, MOV, M4V, or Ogg file, wait for its decoded dimensions, then enter X and Y offsets plus crop width and height in source pixels. The defaults select the full frame. Crop video plays the source locally, draws only the requested region into Canvas, records that Canvas stream as WebM, and offers the resulting file for download. No source or output is uploaded to Lizely.

Coordinates start at the source frame's top-left corner. X moves the crop right, Y moves it down, width controls the horizontal extent, and height controls the vertical extent. Every value must be an untrimmed nonnegative whole pixel count. Width and height must each be at least two pixels. X plus width and Y plus height must remain inside the decoded source, and output area may not exceed 3840 × 2160 pixels. Invalid rectangles fail without shifting, clipping, rounding, or producing a partial file.

Input shares the explicit video safety budget: positive files up to 500 MiB, decoded duration above zero and no more than five minutes, no source side above 4096 pixels, and no source area above 3840 × 2160. An accepted extension does not guarantee codec support; decoding depends on the current browser. Processing occurs in real time, so a one-minute source takes about one minute while the tab remains open.

The output uses the first browser-reported WebM recorder among VP9, VP8, and generic WebM. Requested video bitrate derives from cropped pixel area at 30 frames per second and is bounded from 180 kbps through 8 Mbps. This is a disclosed single-pass browser setting, not a guarantee of target size or visual quality. Fast motion, noise, grain, source codec, and browser encoder can change size and quality. Keep the original until the entire output has been reviewed.

When the browser exposes an audio track through media capture, the tool appends it to the Canvas stream. Support varies, and the source may play audibly during real-time processing. Verify both sound and picture. The crop does not preserve subtitles, chapters, attachments, rotation tags, HDR signaling, color metadata, or every container feature. It changes the visible frame region; it is not a trim-by-time, resize, compress-only, redact, blur, or object-removal tool.

Streaming MediaRecorder output may omit a finite container duration. After recording, the tool uses the already standards-tested WebM duration writer shared with Video Compressor: it parses Segment Info and TimestampScale and inserts a big-endian Matroska Duration value in timestamp-scale ticks. The result must remain nonempty and decode with the requested dimensions. Object URLs, timers, recorder tracks, and playback are stopped or released on replacement, error, stale completion, or unmount.

Use exact coordinates when a platform requires a known frame or when unwanted edges are static throughout a clip. This tool applies one rectangle to every frame; it does not track a moving subject or change the rectangle over time. Preview the original dimensions, calculate a rectangle that stays inside them, download the WebM, and confirm duration, crop, audio, and compatibility in the destination player before deleting anything.

Methodology & sources

Reuse the audited video file, decoded-dimension, duration, and WebM Duration gates from Video Compressor. Parse X, Y, width, and height as untrimmed whole pixels; require nonnegative offsets, dimensions of at least two, a rectangle entirely inside the source, and output area no larger than 3840 × 2160. Draw the fixed source rectangle into an equal-size opaque Canvas at 30 fps, append capturable audio when available, request bounded bitrate from cropped area, record VP9/VP8/WebM, insert finite Matroska Duration in TimestampScale ticks, require a nonempty Blob, and release all timers, tracks, playback, and URLs on every exit path.

Frequently asked questions

Does cropping upload my video?
No. Decode, Canvas crop, WebM recording, duration patching, and download all happen in the current tab.
What do X and Y mean?
They are pixel offsets from the source frame's top-left corner. X moves right and Y moves down.
Can the crop move during the video?
No. One fixed rectangle is applied to every frame; the tool does not track people or objects.
Will audio and metadata be preserved?
Audio is included only when the browser exposes a capturable track. Subtitles, chapters, rotation, HDR, and many metadata fields are not preserved, so review the result.

Related tools