A video crop tool that runs locally in your browser lets you trim the visible frame area of a single source video without uploading anything, but the result is a fixed-rectangle WebM — not a tracked, resized, or retimed clip. Before you use Video Cropper, the essentials to know are that your source must be a browser-decodable file at or under 500 MiB and five minutes of decoded duration, with no side longer than 4096 pixels and a total area no larger than 3840 × 2160; that X, Y, width, and height are untrimmed whole-pixel counts starting from the source frame's top-left corner with width and height each at least two pixels; that the rectangle must stay inside every decoded frame and the output area must also stay within 3840 × 2160; that the output is WebM (VP9, VP8, or generic) at roughly 30 fps with a bitrate derived from the cropped pixel area between 180 kbps and 8 Mbps; that audio is appended only when the browser exposes a capturable track; and that subtitles, chapters, attachments, rotation tags, HDR signaling, and many container metadata fields are not preserved.
What Source Files Video Cropper Accepts
Before you open Video Cropper, the most important thing to confirm is what kind of source file actually works. The tool accepts a video file your browser can decode — typically MP4, WebM, MOV, M4V, or Ogg — but an accepted extension is not the same as a confirmed decode. The current browser still has to decode the file before any cropping can start, and until the decoded dimensions appear in the interface, no coordinate you type is meaningful.
The input shares the same explicit safety budget used by other local video tools on Lizely: the file must be at or under 500 MiB, the decoded duration must be greater than zero and no longer than five minutes, no source side may exceed 4096 pixels, and no source area may exceed 3840 × 2160 pixels. If any of these are exceeded, the tool rejects the file rather than silently clipping or resampling it.
| Property | Limit |
|---|---|
| File size | Up to 500 MiB |
| Decoded duration | Greater than 0 and at most 5 minutes |
| Largest source side | No more than 4096 pixels |
| Source frame area | No more than 3840 × 2160 pixels |
| Container extensions accepted | MP4, WebM, MOV, M4V, Ogg |
| Codec compatibility | Depends on the current browser, not on the extension |
If your file fails any of these checks, Video Cropper will not load its dimensions and cropping cannot proceed. Trim or compress the source first if you need to bring it inside the budget — for example by trimming a longer clip with Video Trimmer or re-encoding an oversized file with Video Compressor.
How the X, Y, Width, and Height Coordinates Work
The crop is a single rectangle described by four numbers, and every one of them is a whole-pixel count measured from the top-left corner of the decoded source frame. X is the horizontal offset that moves the rectangle to the right; Y is the vertical offset that moves it down; width is the horizontal extent of the rectangle; and height is the vertical extent. None of these values is trimmed, scaled, or rounded — they are taken literally, and any fractional or negative input is rejected.
A few rules make the coordinate math unambiguous. Both width and height must be at least two pixels. X plus width and Y plus height must each stay inside the decoded source frame for every frame. The output area (width times height) must also stay at or below 3840 × 2160 pixels. If you ask for a rectangle that runs off the edge of any frame, the tool fails without shifting, clipping, rounding, or producing a partial file.
Two practical consequences are worth knowing up front. First, the crop is fixed for the entire clip — one rectangle applied to every frame, with no tracking of a moving subject and no change over time. If your subject drifts across the frame, the rectangle will follow the frame, not the person. Second, the defaults select the full frame, so if you only want to remove a thin strip of unwanted edge, the math is "subtract the strip width from the source width," not "subtract from width as displayed." Always preview the source dimensions first and calculate a rectangle that stays inside them.
What the Output WebM Will and Won't Include
Knowing the output format before you click prevents surprises after the recording finishes. Video Cropper records the cropped Canvas as a WebM file — drawing only the requested rectangle into a same-size opaque Canvas at roughly 30 fps per the WHATWG HTML Canvas drawImage specification, then capturing that Canvas stream via the browser's MediaRecorder — using the first codec the browser reports among VP9, VP8, and generic WebM. The target bitrate is derived from the cropped pixel area and bounded between 180 kbps and 8 Mbps. Because the encoder is the browser's own MediaRecorder, fast motion, noise, grain, the source codec, and the browser version all influence the final size and visual quality — the bitrate target is a disclosed setting, not a guaranteed file size or quality level.
Audio is included only when the browser exposes a capturable audio track through media capture. Many browsers do expose one, but support varies, and the source may play audibly during real-time processing — close other audio before you start if that matters. The crop does not preserve subtitles, chapters, attachments, rotation tags, HDR signaling, color metadata, or every other container feature. Streaming MediaRecorder output may also omit a finite container duration, which is why Video Cropper runs the same standards-tested WebM duration writer used by Video Compressor: it parses Segment Info and TimestampScale and inserts a big-endian Matroska Duration value in timestamp-scale ticks. The patched file must remain nonempty and decode with the requested dimensions, or it is rejected.
| Aspect | Behavior in the output WebM |
|---|---|
| Container | WebM (VP9, VP8, or generic WebM, browser-chosen) |
| Frame rate | Approximately 30 fps |
| Bitrate target | 180 kbps to 8 Mbps, derived from cropped pixel area |
| Audio track | Included only when the browser exposes a capturable track |
| Subtitles | Not preserved |
| Chapters | Not preserved |
| Rotation tags | Not preserved |
| HDR signaling | Not preserved |
| Color metadata | Not preserved |
| Container duration | Patched to a finite value via the WebM duration writer |
It is also worth knowing what this tool is not. Video Cropper changes the visible frame region — it is not a trim-by-time tool, not a resize tool, not a compress-only tool, not a redaction tool, not a blur tool, and not an object-removal tool. If you need any of those, you should reach for the matching local tool instead — Video Trimmer for time ranges, Video Resizer for output dimensions, and Video Compressor for re-encoding within a target size.
How to Crop a Video With Video Cropper
Once your file passes every input check and your rectangle math is done, the actual cropping is a short, three-step procedure that runs locally in your current tab.
- Choose a browser-decodable video and wait for its source dimensions to load. Do not enter coordinates until the decoded width and height appear — the tool needs them to validate any rectangle you type.
- Enter whole-pixel X, Y, width, and height values that stay inside every source frame. Double-check that width and height are each at least 2 pixels, that no value has stray whitespace that would change parsing, and that X + width and Y + height each remain inside the decoded source.
- Select Crop video, keep the tab open during real-time processing, then download and fully review the WebM. A one-minute source takes roughly one minute to record; closing the tab, refreshing, or navigating away cancels the export.
Open Video Cropper in a desktop browser, follow those three steps, and the resulting file lands on your device without ever leaving your machine.
What to Verify Before You Delete the Original
A cropped WebM that opens and plays back is not necessarily a correct crop. Before you delete or overwrite your source file, play the output in the same player or platform where it will end up and confirm four things: the duration matches what you expected (the patched finite duration should not be zero or wildly off); the picture shows exactly the rectangle you asked for, with no edge artifacts and no part of the unwanted area peeking in; the audio, if any, is present, in sync, and at a sensible level; and the file actually plays on the destination device or upload target without re-encoding prompts.
Because the encoder is the browser's MediaRecorder and the bitrate target is derived from pixel area rather than from a target size, file size and visual quality can drift. Fast motion, noise, grain, the source codec, and the browser version all change the result. Treat the bitrate band of 180 kbps to 8 Mbps as the disclosed range the encoder can land in, not a promise. If the picture looks softer than the source, or the file is much larger than you expected, re-run the crop or run the output through Video Compressor to re-encode within an explicit size band. If something still looks wrong after that, the Video Crop failure map walks through the most common causes and fixes.
Object URLs, timers, recorder tracks, and playback inside the tool are stopped or released on replacement, error, stale completion, or unmount, so leaving the page does not leak memory, but it does discard any in-progress recording. Plan to start, watch, and download in one session, and keep the original on disk until the output has been reviewed end to end.
Related reading: What to Review After You Use Video Crop.