To crop a video for Instagram Reels, set X, Y, width, and height in source pixels so the resulting rectangle is a 9:16 frame — typically 1080 × 1920 — then re-record that exact region in your browser and download the WebM. The Video Cropper does exactly that: it loads a browser-decodable source, lets you enter whole-pixel coordinates that stay inside every frame, plays the source locally while drawing only the requested region into a Canvas (see the WHATWG HTML Canvas drawImage spec), and saves that Canvas stream as a WebM with a finite Matroska Duration patched in. Because everything happens in the current tab, the source file and the cropped output are never uploaded. Processing is real-time, so a one-minute clip takes about one minute to record, and the tab must stay open until the download link appears. The output uses the first browser-supported WebM codec (VP9, VP8, or generic WebM), with bitrate bounded from 180 kbps to 8 Mbps and clipped to a 3840 × 2160 maximum output area. Audio is appended only when the browser exposes a capturable track through media capture, so listen to the result before posting. Subtitles, chapters, rotation tags, HDR signaling, and most container metadata are dropped during the crop, and a single fixed rectangle is applied to every frame — the tool does not track a moving subject. Plan the rectangle from the source's decoded dimensions, keep the original until you have reviewed the WebM end to end, and confirm Reels accepts the file in your account before deleting anything.
What "Crop Video for Instagram Reels" Actually Means
Cropping for Reels is a spatial operation, not a temporal one: you select a sub-rectangle of every frame in the source and discard the rest. The clip keeps its full duration and (when supported) its original audio track, with the output recorded at a fixed 30 fps. The recommended source resolution for Reels is 1080 × 1920 pixels at a 9:16 aspect ratio, which is why most cropping guides for Reels focus on that target. Instagram also accepts a few other frame sizes, but vertical 9:16 is the native shape of the Reels player. For a broader rundown of upload specs across feed, Stories, and Reels, see the best video format for Instagram guide. The Video Cropper does not resize or scale; it draws a fixed rectangle from the source frame into an equal-size Canvas at a fixed 30 fps and records the result. If your source is, say, a 3840 × 2160 master, the rectangle inside it is 9:16 but at the source's own resolution, not at 1080 × 1920, so a 4K source produces a 4K 9:16 WebM and a 1080-tall source produces a 1080-tall 9:16 WebM. Plan accordingly.
Why a Fixed Pixel Rectangle Is the Right Tool
Aspect-ratio presets in editor apps are convenient, but they hide off-by-one pixel issues that platforms sometimes reject. By typing exact source pixels for X, Y, width, and height, you can reproduce the same crop on another source, audit a clip that a collaborator sent, or target a specific static region that is present in every frame. Coordinates are pixel offsets from the top-left corner of the decoded source: X moves the rectangle 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, and both width and height must be at least 2 pixels. X plus width and Y plus height must remain inside every decoded source frame, and the resulting output area may not exceed 3840 × 2160 pixels. An invalid rectangle fails without shifting, clipping, rounding, or producing a partial file, so a successful run reflects the exact numbers you entered.
How to Crop a Video for Instagram Reels in Your Browser
- Open the Video Cropper and pick a browser-decodable source file. The tool accepts MP4, WebM, MOV, M4V, or Ogg by extension, though the actual codec must be one the current browser can decode. Wait for the source's decoded dimensions to appear before continuing.
- Enter X and Y as nonnegative whole-pixel offsets from the top-left of the frame. Then enter width and height in whole pixels. Each dimension must be at least 2, X + width must not exceed the source width, and Y + height must not exceed the source height.
- Check that the rectangle yields a 9:16 ratio (or whatever shape Reels needs in your case). For a 1080 × 1920 source, X=0, Y=0, width=1080, height=1920 selects the full frame.
- Click Crop video. Keep the tab open and the system awake during real-time processing; a one-minute source takes roughly one minute.
- When the download link appears, save the WebM to a known location and play it from start to finish in a player that respects the patched Matroska Duration.
- Listen for audio, confirm the crop, confirm the duration, and only then delete the original.
Sizing the 9:16 Rectangle From Your Source Dimensions
The math behind a 9:16 crop is straightforward. A 9:16 rectangle has a width-to-height ratio of 9 ÷ 16, so once you fix one dimension, the other is determined. Common targets include:
- 1080 × 1920 — the recommended Reels source. Width = 1080, height = 1080 × 16 ÷ 9 = 1920.
- 1215 × 2160 — fits inside a 3840 × 2160 source. Height = 2160, width = 2160 × 9 ÷ 16 = 1215.
- 608 × 1080 — fits inside a 1920 × 1080 source. Height = 1080, width = 1080 × 9 ÷ 16 = 607.5.
Worked example: a 3840 × 2160 source and a 9:16 rectangle. The rectangle is height-limited, so height = 2160 and width = 2160 × 9 ÷ 16 = 1215. Rounding to the nearest even pixel for encoder friendliness gives width = 1216. To center the strip horizontally, X = (3840 − 1216) ÷ 2 = 1312, and Y = 0. So the inputs are X=1312, Y=0, width=1216, height=2160. Verify: 1312 + 1216 = 2528 ≤ 3840, and 0 + 2160 = 2160 ≤ 2160. Aspect: 1216 ÷ 2160 ≈ 0.56296, which is 9 ÷ 16 within rounding. A 1920 × 1080 horizontal source has a different limit: 1080 vertical pixels only fits a 9:16 rectangle of 608 × 1080, not 1080 × 1920, so a horizontal source needs vertical pixels added (out of scope for a crop-only tool) or a different approach.
What the Cropper Keeps, Drops, and Refuses
The crop changes the visible frame region and that is the entire scope of the tool. It is not a trim-by-time, a resize, a compress-only, a redact, a blur, or an object-removal tool. The following table summarizes what survives the crop, what is conditional, and what is dropped:
| Property | Status after crop |
|---|---|
| Visible frame region | Replaced by your fixed X, Y, width, height rectangle, drawn into an equal-size Canvas. |
| Audio | Appended to the Canvas stream only when the browser exposes a capturable track through media capture; support varies. |
| Subtitles, chapters, attachments | Not preserved. |
| Rotation tags, HDR signaling, color metadata | Not preserved. |
| Container features beyond Matroska Duration | Not all preserved; only the standards-tested Duration writer is applied after recording. |
| Frame rate, duration | Source duration is kept; the output frame rate is a fixed 30 fps; the WebM gets a finite Matroska Duration in timestamp-scale ticks (per the Matroska container format). |
The tool also enforces hard limits before and during the crop. Anything outside these limits fails without producing a partial file:
| Limit | Value |
|---|---|
| Source file size | Positive, up to 500 MiB. |
| Source duration | Above zero, no more than 5 minutes. |
| Source side | No dimension above 4096 pixels. |
| Source area | No area above 3840 × 2160 pixels. |
| Output area | No area above 3840 × 2160 pixels. |
| Crop dimensions | Width and height each at least 2 pixels. |
| Coordinate format | Untrimmed, nonnegative whole pixels. |
| Output bitrate | Derived from cropped area at 30 fps, bounded 180 kbps to 8 Mbps. |
| Output codec | First browser-supported WebM among VP9, VP8, generic WebM. |
Verifying the Cropped WebM Before You Post
Reels rejects files that drift outside its accepted container or that fail its own re-encode, so a quick verification pass saves a re-export. Play the cropped WebM from start to finish in a player that honors the patched Matroska Duration; missing duration usually shows up as an unknown length in tools that do not parse Segment Info and TimestampScale. Scrub through to confirm the rectangle does not cut off a face, a logo, or any text that needs to stay on screen. Listen for audio, because the source may have played audibly during real-time processing even when the output is silent. If you need a different codec, a tighter size, or a transcode to MP4, the Video Compressor can re-encode the WebM locally as a bounded WebM with a small, balanced, or quality preset. Only after the full clip is approved should you delete the source.
For a deeper look, see Best Video Format for Instagram Reels and How to Resize.