Using a browser-based video crop tool produces a WebM file whose dimensions exactly match the pixel rectangle you specified, recorded from your source in real time inside the current tab and patched with a finite duration before download. The output is not a re-encode of your entire source — it is a re-recording of a single in-frame region drawn into a Canvas element, captured by MediaRecorder, and finalized locally so nothing leaves your browser. When the source frame is 1920 × 1080 and you request X = 200, Y = 100, width = 1200, height = 800, the file you receive plays back at exactly 1200 × 800 pixels with the chosen offset preserved on every frame. The rectangle is static, the container is WebM (the first codec the browser reports among VP9, VP8, or generic WebM), and the tool inserts a finite Matroska Duration so players do not treat the result as a live stream. If you have not used a crop tool before, this is the concrete shape of the deliverable: a bounded WebM, drawn from one rectangle, ready for download after real-time processing completes.
The Output File You Will Download
The output is always a WebM. The tool writes the file from a Canvas-backed MediaRecorder stream, then patches the container's Segment Info and TimestampScale so the Duration field is finite. Without that patch, browsers commonly emit a WebM that players flag as a live stream with no end. The file you receive decodes at exactly the width and height you entered, expressed in whole source pixels, with each dimension required to be at least two pixels and the resulting rectangle bounded by the source frame on every side.
Output area is capped at 3840 × 2160 pixels — a ceiling that covers 4K UHD. Inputs that would produce a larger rectangle are rejected without shifting, clipping, rounding, or producing a partial file. The bitrate the recorder requests is derived from the cropped pixel area at 30 fps and falls between 180 kbps and 8 Mbps; this is a disclosed browser setting, not a guaranteed target size, so final file size will vary with motion, noise, grain, source codec, and the encoder your browser hands you. For a single-step worked check, take a 1920 × 1080 source and request X = 200, Y = 100, width = 1200, height = 800:
- X + width = 200 + 1200 = 1400, which must be ≤ 1920 ✓
- Y + height = 100 + 800 = 900, which must be ≤ 1080 ✓
- output area = 1200 × 800 = 960,000 pixels, well under 3840 × 2160 ✓
When all three checks pass, the recorder starts. When any one fails, no file is produced.
How the Crop Affects the Visible Picture
Every output frame contains the exact same rectangular region from the source, drawn into a Canvas that matches the cropped size. The rectangle does not move, resize, or track anything over time. If the unwanted area is static — a black bar, a fixed logo in one corner, a watermark that never shifts — a single rectangle removes it from the entire clip. If the unwanted area moves, the crop will keep cutting out the same coordinates and the offending region will simply appear somewhere else in the output. The tool is not designed for object removal, motion tracking, or zoom-and-pan effects, and it does not slide the rectangle to follow a subject.
Coordinates are read from the source frame's top-left corner. X moves the rectangle right, Y moves it down, width controls how far the rectangle extends horizontally, and height controls the vertical extent. Every value is an untrimmed nonnegative whole pixel count — decimals, leading or trailing whitespace, and negative numbers all fail the input gate. The defaults populate the full frame, which is why a fresh load of any source will produce a file identical to the input's dimensions before you change anything.
Audio, Metadata, and Container Features
Audio is preserved only when the browser exposes the source's audio track through media capture. Where supported, the tool appends that track to the Canvas stream so the output WebM carries both picture and sound. Where the browser does not expose audio — or where the source has no audio track to begin with — the output is silent. Because support varies and the source may play audibly during real-time processing, you should verify both sound and picture in the destination player before deleting the original.
Most container features are not preserved. The crop does not carry over subtitles, chapters, attachments, rotation tags, HDR signaling, or most color metadata. It is also not a trim-by-time, resize, compress-only, redact, blur, or object-removal tool. If you need time-based trimming, a separate trim operation is required; if you need a different encoded size without removing edges, that is a resize workflow. The crop changes only the visible frame region. Keep the original until the entire output has been reviewed.
| Property | Behavior After Crop |
|---|---|
| Visible frame region | Replaced by your requested rectangle |
| Pixel dimensions | Equal to width × height you entered |
| Container | WebM (VP9, VP8, or generic WebM) |
| Duration field | Finite Matroska Duration inserted |
| Audio | Included only when browser exposes a capturable track |
| Subtitles, chapters, rotation, HDR | Not preserved |
| Original source file | Unchanged; not uploaded |
Crop a Video Locally With Video Cropper
To get this result yourself with the Video Cropper tool, follow these steps:
- Choose a browser-decodable video — MP4, WebM, MOV, M4V, or Ogg — and wait for the source dimensions to populate. Decoding depends on the current browser, so an accepted extension is not a guarantee of support.
- Enter whole-pixel X, Y, width, and height values that stay inside every source frame. Width and height must each be at least two pixels, and the rectangle's right and bottom edges cannot exceed the decoded source dimensions.
- Select Crop video. The source plays locally, the tool draws only the requested region into Canvas, and a WebM stream is recorded at 30 fps with bounded bitrate. Keep the tab open during this real-time processing — a one-minute source takes about one minute.
- Download the WebM once the recorder finishes, and fully review the result. Confirm duration, picture, audio (if expected), and compatibility in the destination player before deleting the original.
Invalid rectangles fail without shifting, clipping, rounding, or producing a partial file. Object URLs, timers, recorder tracks, and playback are stopped or released on replacement, error, stale completion, or unmount.
What Can Change the Result You Get
Several variables influence the file even when your coordinates are correct. The first browser-reported WebM recorder among VP9, VP8, and generic WebM is used, so different browsers expose different codecs and identical inputs can produce files of slightly different sizes and quality. Requested bitrate is derived from cropped pixel area at 30 fps and is bounded between 180 kbps and 8 Mbps, which means a small crop may request a low bitrate and yield a smaller file while a near-full-frame crop may request a higher bitrate and yield a larger file.
Fast motion, film grain, and high-frequency noise cost more bits at the same encoder settings, and the disclosed bitrate range is a browser setting rather than a guarantee of visual quality. When the browser does not expose audio through media capture, the output is silent regardless of the source. Because processing happens in real time, a five-minute source takes about five minutes; closing or backgrounding the tab interrupts the recording.
The input layer enforces a shared 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. Files that exceed any of those limits are not accepted. If your source is longer than five minutes, trim it first before cropping.
For more on how pixel choices and audio availability affect the final file, see the Video Cropper accuracy guide on pixels, audio, and duration. The output you receive is a precise, bounded artifact — not a live stream, not a partial file, not a re-encoded full source — so verification in your destination player is the final step before you commit to deleting the original.
Related reading: What to Know Before You Use Video Crop as a Beginner.