Yes — a video can be cropped entirely inside your browser without uploading a file to any server, by decoding the source locally and re-recording only the requested rectangle as WebM. Lizely's Video Cropper keeps the source on your device: when you select a file, the browser reads it as a local resource, decodes its frames, draws only the requested rectangle into a Canvas, and records that Canvas stream as WebM for download. Nothing is sent to a remote server, no account is required, and the original file remains untouched. The trade-off is that this local approach replaces a server round-trip with real-time processing — the recorder plays the source at normal speed while the tab stays open, so a one-minute clip needs roughly one minute to finish. The tool is also constrained by what your current browser can decode (commonly MP4, WebM, MOV, M4V, and Ogg) and by an explicit safety budget that is checked before recording ever begins.
Why a Local Cropper Means No Upload
The privacy promise of a browser-local cropper rests on a simple fact: every step happens inside the tab you already have open. The file picker returns a local handle that the browser decodes via its own media stack — there is no fetch call to a backend, no multipart upload, and no presigned URL pointing to cloud storage. Once the decoded dimensions load, the tool draws each frame into a Canvas using the source video element as input and reads that Canvas back through a capture stream. The stream feeds a MediaRecorder that produces a WebM Blob in memory; the only network traffic you will see while cropping is whatever your browser does for telemetry, which is outside the tool's control. For readers who want to confirm this themselves, the WHATWG HTML specification describes how drawImage works on video elements without ever leaving the page.
This architecture has practical consequences. Because nothing leaves your machine, there is nothing to delete on a server afterward — but there is also no cloud recovery if you close the tab mid-export. The original file is never modified, so deleting it before you have finished reviewing the output is your decision alone. The recorder plays the source through speakers in some browsers, so if you are cropping in a quiet room, mute the source tab or use headphones before you click Crop video.
Input Limits and Browser-Decodable Files
Before any pixel coordinate is read, the tool checks the source against an explicit safety budget. Files larger than 500 MiB, longer than five minutes once decoded, with any side above 4096 pixels, or with a total area above 3840 × 2160 are refused outright. The accepted extensions are MP4, WebM, MOV, M4V, and Ogg, but the contract is explicit that an accepted extension does not guarantee codec support — decoding depends on the browser you happen to be using. A MOV file with an unusual codec might decode on Chrome but not on Firefox, and the tool will surface that as an inability to read dimensions, not as a silent failure.
| Constraint | Limit |
|---|---|
| Maximum source file size | 500 MiB |
| Maximum decoded duration | 5 minutes (must be above zero) |
| Maximum source side | 4096 pixels |
| Maximum source area | 3840 × 2160 pixels |
| Accepted extensions | MP4, WebM, MOV, M4V, Ogg |
| Output area ceiling | 3840 × 2160 pixels |
Output area is bounded even more tightly than source area. The contract states that the cropped rectangle itself may not exceed 3840 × 2160, which means a 3840 × 2160 source can be cropped in full but cannot be combined with an offset that pushes the rectangle partially outside the frame.
Reading the X, Y, Width, and Height Fields
The crop is defined by four numbers: X, Y, width, and height. All four are whole-pixel counts in the source frame's coordinate system. X is the horizontal offset measured from the top-left corner of every frame; Y is the vertical offset measured from the same corner; width is how many pixels to the right of X the rectangle extends; height is how many pixels below Y the rectangle extends. The defaults select the full frame, so leaving every field at its default crops nothing.
The rectangle must stay entirely inside the source. Two checks are applied: X plus width cannot exceed the source width, and Y plus height cannot exceed the source height. Every value must be a nonnegative whole number, and width and height must each be at least two pixels — a one-pixel crop is rejected. Invalid rectangles fail without shifting, clipping, rounding, or producing a partial file, which is why pre-checking the math matters before you click Crop video.
A worked example illustrates the constraints. Suppose the source is 1920 × 1080 and you want to keep the central 1280-pixel-wide, 720-pixel-tall region. You would set X to (1920 − 1280) / 2 = 320, Y to (1080 − 720) / 2 = 180, width to 1280, and height to 720. Verifying: X + width = 320 + 1280 = 1600, which is less than or equal to the source width of 1920; Y + height = 180 + 720 = 900, which is less than or equal to 1080. The output area is 1280 × 720 = 921,600 pixels, well under the 3840 × 2160 ceiling of 8,294,400 pixels.
How to Crop a Video Without Uploading
- Choose a browser-decodable video (MP4, WebM, MOV, M4V, or Ogg) from your local drive and wait for the decoded source dimensions to appear next to the X, Y, width, and height fields.
- Enter whole-pixel values into X, Y, width, and height, making sure X + width stays within the source width and Y + height stays within the source height.
- Select Crop video and keep the tab open. The source plays through once in real time while the recorder draws the requested rectangle into a Canvas.
- When the source finishes playing, click the download control to save the resulting WebM file to your device.
- Open the downloaded WebM in your destination player and review the entire clip for frame content, audio, and duration before deleting the original.
The fifth step is the one most readers skip. A browser-local cropper alternative can look identical to a cloud cropper on the surface, but the difference is that you are the only safety net once the tab closes.
How the Output WebM Is Built
The output format is WebM, not MP4, because WebM is the container that browser MediaRecorder implementations emit natively. The recorder picks the first available codec from a fixed preference list — VP9 first, then VP8, then generic WebM — so the exact encoder depends on the browser you used. Requested bitrate derives from the cropped pixel area at 30 fps and is clamped between 180 kbps and 8 Mbps: a small crop stays near the floor, a near-ceiling crop pushes toward 8 Mbps. This is a single-pass browser setting rather than a guarantee of target file size or visual quality, so fast motion, noise, grain, source codec, and the encoder itself can push the actual result above or below the requested bitrate.
Streaming MediaRecorder output typically omits a finite container duration, which is why the WebM file might play past the end in some players. To prevent that, the tool parses the recorded file's Segment Info and TimestampScale elements and inserts a big-endian Matroska Duration value in timestamp-scale ticks, the same standards-tested writer used by Video Compressor. The final Blob must be nonempty and must decode at the requested dimensions; if either check fails, the export is rejected.
What This Tool Does Not Change
A pixel crop is a frame-region operation, not a general video editor. It is not a trim-by-time tool, not a resize, not a compress-only operation, not a redact or blur, and not an object-removal feature. Subtitles, chapters, attachments, rotation tags, HDR signaling, and most color metadata are not preserved. Audio is included only when the browser exposes a capturable track through media capture; support varies by browser and may also depend on whether the source codec contains a track the browser knows how to record.
| Property | Behavior after crop |
|---|---|
| Visible frame region | Changes to the requested rectangle on every frame |
| Output container | WebM (VP9, VP8, or generic, browser-dependent) |
| Output duration | Source duration, with finite Matroska Duration patched in |
| Audio | Included only if the browser exposes a capturable track |
| Subtitles, chapters, attachments | Not preserved |
| Rotation tags, HDR, color metadata | Not preserved |
| Crop motion tracking | None — one fixed rectangle for the whole clip |
Because one rectangle is applied to every frame, this is the right tool when the unwanted edges are static throughout a clip — for example, removing letterbox bars or a watermark stuck in one corner. It is the wrong tool when the subject moves across the frame and you want the crop to follow.
Verifying the Result Before Deleting the Source
Local processing means local responsibility. Once the tab closes, the recorder, the object URL pointing at the source, the playback element, and any timers are released; reopening the tool will not recover an in-progress export. Because of that, the safe workflow is to keep the original file on disk until you have watched the entire WebM from start to finish in the player where it will actually be used. Confirm the crop coordinates, confirm the audio is present if you expected it, confirm the duration matches the source, and confirm the file opens cleanly in the destination player. Only then delete the original.
If you're weighing options, Can the Crop Move During the Video in a Video Cropper? covers this in detail.