A video cropper is a tool that removes the outer area of a video by re-recording an exact rectangular region defined in source pixels, then exports the result as a new file. The rectangle is measured in whole pixels from the top-left corner of every frame: X moves the crop right, Y moves it down, width sets the horizontal extent, and height sets the vertical extent. Because the same rectangle is applied to every frame, a video cropper is the right tool when the unwanted area stays in the same place throughout a clip, such as a static logo bar, a hardcoded caption, or a fixed black border. It is not a trim-by-time tool, a resize tool, or a compressor, and it does not track moving subjects. The Video Cropper implements this concept locally in the browser, drawing the requested region into a Canvas element, recording that canvas as a WebM file, and patching a finite duration into the container so the output plays correctly in standard players. The source file and the output never leave the tab.
Cropping vs. Resizing, Trimming, and Compressing
The term "video cropper" is easy to confuse with three other common video operations. Each one changes the file in a different way, and choosing the wrong one can ruin an otherwise simple edit. A cropper narrows the visible rectangle inside every frame without touching the timeline or the resolution. A resizer changes the resolution of every frame without changing which pixels are visible. A trimmer cuts the timeline by removing frames from the start, the end, or both. A compressor reduces bitrate and file size without changing what the eye sees.
| Operation | What changes | What stays the same | Typical use |
|---|---|---|---|
| Crop | The visible frame region (X, Y, width, height in pixels) | Frame count and playback timeline | Remove a static border, logo, or unwanted edge |
| Resize | The output resolution of every frame | Aspect ratio unless explicitly stretched | Fit a target resolution such as 1080p or 720p |
| Trim | The start and end time of the clip | Every frame between those times | Cut a short segment from a longer recording |
| Compress | The file size and bitrate | Frame dimensions and visible content | Reduce a file for sharing or upload limits |
A cropper sits at the top of this list. It does not change resolution (that is resizing), it does not change duration (that is trimming), and it does not lower bitrate (that is compressing). It only narrows the visible rectangle inside every frame, which is why the output of a crop is often handed off to a compressor or a resizer for a second pass.
How the Video Cropper Works in Your Browser
The Video Cropper follows the same local-processing pattern as the rest of the Lizely video tools. Nothing is uploaded. The source file is decoded in the browser using the built-in video element, and the tool waits for the decoded dimensions to become available before accepting any coordinate input. An accepted file extension such as MP4, WebM, MOV, M4V, or Ogg does not guarantee that the current browser can decode the codec inside the file, so the dimensions check is the real gate.
When you select Crop video, the tool plays the source locally and draws only the requested rectangle into an equal-size opaque Canvas element at roughly 30 frames per second. The Canvas stream is captured by the browser's MediaRecorder and encoded as WebM, using the first supported codec the browser reports among VP9, VP8, and generic WebM. According to the IETF Matroska Media Container Format, a streaming MediaRecorder output may omit a finite container duration, so the tool inserts a big-endian Matroska Duration value expressed in TimestampScale ticks once recording stops, matching the standards-tested WebM duration writer used by Video Compressor. The result must remain nonempty and decode at the requested dimensions.
Audio is appended to the Canvas stream when the browser exposes a capturable audio track through media capture. Support varies by browser and source codec, so the source may play audibly while the tab processes the clip in real time. The target bitrate is derived from the 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, because fast motion, noise, grain, source codec, and the browser encoder all change the final file.
How to Crop a Video With the Video Cropper
Three steps cover the full workflow. Each step maps directly to a verified control on the Video Cropper page.
- Choose a browser-decodable video and wait for its source dimensions to load. The tool accepts MP4, WebM, MOV, M4V, or Ogg files within the shared safety budget, but an accepted extension does not guarantee that the current browser can decode the codec inside it. Wait until the tool reports the decoded width and height before continuing.
- Enter whole-pixel X, Y, width, and height values that stay inside every source frame. X and Y are offsets from the top-left corner; width and height set the rectangle. Every value must be an untrimmed nonnegative whole number, both dimensions must be at least two pixels, and the rectangle must remain entirely inside the decoded source. The defaults select the full frame.
- Select Crop video, keep the tab open during real-time processing, then download and fully review the WebM. Processing happens in real time, so a one-minute source takes about one minute. Keep the tab focused and do not navigate away until the download link appears, then play the file in your destination player to confirm duration, crop, audio, and compatibility before deleting the original.
For example, if the decoded source is 1920 × 1080 and you want a centered 1280 × 720 crop, the X offset is (1920 − 1280) ÷ 2 = 320 and the Y offset is (1080 − 720) ÷ 2 = 180. Enter X = 320, Y = 180, width = 1280, height = 720, and verify that 320 + 1280 = 1600 stays inside 1920 and that 180 + 720 = 900 stays inside 1080. Invalid rectangles fail without shifting, clipping, rounding, or producing a partial file, so an out-of-bounds value simply blocks the crop until you correct it.
If you are new to coordinate-based cropping, the plain-English walkthrough in Video Cropper for Beginners: A Plain-English Walkthrough covers the same controls with extra examples.
Input Limits and Coordinate Rules
The Video Cropper enforces a set of hard limits. Anything outside these limits is rejected before recording starts, which is why the tool can guarantee a valid WebM without partial files, silent clipping, or silent rounding.
| Limit | Value | Where it applies |
|---|---|---|
| Maximum source file size | 500 MiB | Input safety budget |
| Decoded source duration | Above zero, up to 5 minutes | Input safety budget |
| Maximum source side | 4096 pixels | Input safety budget |
| Maximum source area | 3840 × 2160 pixels | Input safety budget |
| Maximum output area | 3840 × 2160 pixels | Coordinate check |
| Minimum width and height | 2 pixels each | Coordinate check |
| Coordinate type | Untrimmed nonnegative whole pixels | Coordinate check |
| Output container | WebM with finite Matroska Duration | Recorder plus duration writer |
| Output video codec | First browser-reported among VP9, VP8, generic WebM | MediaRecorder selection |
| Output target bitrate | Bounded from 180 kbps through 8 Mbps, derived from cropped area at 30 fps | Recorder configuration |
| Output audio | Included only when the browser exposes a capturable track | Media capture |
What Cropping Preserves and What It Drops
The crop changes one thing: the visible rectangle inside every frame. Everything else depends on what the browser recorder can capture alongside the Canvas stream.
- Preserved: the visible pixels inside the rectangle, the playback timeline, and the audio track when the browser exposes a capturable stream.
- Not preserved: subtitles, chapters, attachments, rotation tags, HDR signaling, color metadata, and most other container features. The crop does not guarantee a target output size, because fast motion, noise, grain, source codec, and the browser encoder all change the final bitrate.
Object URLs, timers, recorder tracks, and playback are stopped or released on replacement, error, stale completion, or unmount, which keeps the tab from leaking resources between runs. Because preservation is partial, the contract is explicit: keep the original file until the entire output has been reviewed in the destination player. Confirm duration, crop position, audio, and compatibility before deleting anything.
When Exact-Pixel Cropping Is the Right Choice
Exact-pixel cropping earns its place when the unwanted area is static and the platform or player expects a known frame. Three common cases fit this profile.
Static borders and hardcoded overlays. If a clip carries a permanent lower-third graphic, a watermark, or a fixed black bar, a single rectangle covers every frame without further work. The crop is applied uniformly, so the overlay disappears from the first frame to the last.
Platform-specific framing. When a destination player or social platform expects a known output resolution, the rectangle can be sized to match that resolution so the cropped WebM plays without re-encoding. The output area may not exceed 3840 × 2160 pixels, which covers 4K and below.
Privacy redaction of fixed regions. A pixel rectangle can hide a static name plate, a screen-recorded account number, or a fixed mirror reflection. The crop is a blunt instrument, so this works only when the sensitive region does not move during the clip. For moving subjects, a blur or object-removal tool is the correct choice, and the Video Cropper is not designed for that job.
For clips where the unwanted region moves, or where the edit is about time rather than pixels, the right tool is different. Trimming changes the timeline with Video Trimmer, resizing changes resolution with Video Resizer, and compressing changes bitrate with Video Compressor. A video cropper only changes the visible rectangle, and that single operation is the whole meaning of the word.