Crop a video to TikTok size by extracting a fixed rectangular region in whole source pixels that measures exactly 1080 × 1920 (a 9:16 ratio) and re-recording it as a WebM file. TikTok's upload pipeline is tuned for that frame, so the rectangle's width and height must hit those pixel counts in the source frame, not just visually approximate the shape. The Video Cropper performs that task locally by reading the source video's decoded dimensions, drawing the requested region into a Canvas at 30 fps, appending audio when the browser exposes a capturable track, and recording the canvas stream as a WebM. No source bytes are uploaded at any point, and the same fixed rectangle is applied to every frame, so the crop does not drift, track subjects, or change over time. The crop step changes the visible frame region only; it is not a resize, time trim, blur, redaction, or object-removal pass.
Why TikTok's 1080 × 1920 Frame Forces a Specific Crop
TikTok's main feed is sized for portrait phones, and the platform's documentation and integration guides treat 1080 × 1920 as the reference upload frame. Anything narrower or shorter is letterboxed or zoomed; anything wider is letterboxed with the same effect, and any height mismatch crops the top and bottom in a way the creator did not pick. That means the rectangle you extract from the source must be exactly 1080 pixels wide and 1920 pixels tall in the source's own coordinate system. Approximate values such as "about 1080 × 1920" risk a one- or two-pixel offset that the platform's re-encode will silently clamp, shifting the subject off-center.
This matters most when the source is wider than the target. A 1920 × 1080 landscape clip has plenty of horizontal room but only 1080 pixels of vertical room, which is not enough to reach 1920 without a resize. A 3840 × 2160 clip (4K landscape) has the height to spare, with 2160 vertical pixels, which is enough to host a 1920-pixel-tall rectangle without a resize. If the source is already taller, like 1080 × 1920 phone captures, the crop rectangle can sit exactly at 1080 × 1920 and the result is a true match. The crop tool does not invent pixels; it can only pick a rectangle out of pixels the source already contains.
What Video Cropper Does to Your Video
The Video Cropper is a local browser tool that removes the outer area of one video by re-recording an exact rectangular region you specify. You pick the source file, type four whole-pixel values (X, Y, width, and height), and the tool plays the source locally while it draws only that region into a Canvas at matching resolution. The canvas stream is captured as WebM and offered for download. Nothing is sent to a server, and decoding, drawing, recording, and downloading all happen in the current browser tab.
The crop is fixed for the entire clip: one rectangle is applied to every frame and the rectangle does not move, so the tool does not track a person or an object across frames, change position as the camera pans, or animate a Ken Burns effect. The tool is also explicitly not a time trim, a resize, a compression-only pass, a blur, a redaction, or an object-removal pass. If the source needs to be shortened in time, the Video Trimmer is the right pick. If the source needs to be scaled to a different resolution, the Video Resizer is the right pick. If the source needs to be re-encoded to a smaller file, the Video Compressor is the right pick.
Inputs, Decoded Dimensions, and Hard Limits
Before the tool can crop, it must load the source video's decoded dimensions, which means the file has to be a format the current browser can decode. An accepted file extension does not guarantee codec support; the browser is the final judge. The video also has to satisfy the same safety budget the rest of the local video tools enforce, so it can finish processing without exhausting memory.
The following table lists the bounds the tool enforces on inputs and outputs. Every value is checked before recording starts; a rectangle that breaks any rule is rejected without shifting, clipping, rounding, or producing a partial file.
| Constraint | Limit |
|---|---|
| Source file size | Up to 500 MiB (positive) |
| Decoded duration | Above zero, no more than five minutes |
| Source side length | No side above 4096 pixels |
| Source frame area | No area above 3840 × 2160 pixels |
| Crop rectangle | X + width and Y + height must stay inside the source |
| Crop dimensions | Width and height must each be at least 2 pixels |
| Pixel counts | Nonnegative untrimmed whole numbers only |
| Output area | No larger than 3840 × 2160 pixels |
| Output container | WebM (VP9 if available, then VP8, then generic WebM) |
| Output bitrate | Bounded 180 kbps to 8 Mbps, derived from cropped pixel area at 30 fps |
If a source file passes the file-size and duration gates but the browser cannot decode it, the tool cannot proceed. Re-muxing or re-encoding the source in a different container is a separate step outside the cropper's scope.
How to Crop a Video to TikTok Size Step by Step
The following steps use the verified operating flow and assume the target frame is 1080 × 1920. Substitute your own width and height if a different exact-pixel size is required.
- Open Video Cropper in a desktop browser that can decode your source container (Chrome, Edge, Firefox, or Safari with current codecs).
- Choose a source file from disk: MP4, WebM, MOV, M4V, or Ogg. Wait for the tool to report the source's decoded dimensions; do not enter coordinates until those numbers have loaded.
- Enter the rectangle in whole source pixels. For TikTok's 1080 × 1920 frame, set width to 1080 and height to 1920. Set Y so that Y + 1920 stays inside the source's height, and set X so that X + 1080 stays inside the source's width. X moves the crop right; Y moves it down.
- Confirm the rectangle is valid: X and Y are nonnegative whole numbers, both dimensions are at least two pixels, both edges sit inside the source frame, and the output area of 1080 × 1920 (2,073,600 pixels) does not exceed 3840 × 2160. The tool will reject invalid rectangles without rounding, shifting, or producing a partial file.
- Select Crop video. Keep the tab open and focused while the tool re-records the canvas in real time at source playback speed; a one-minute source takes about one minute, and a five-minute source takes about five minutes.
- When the download link appears, save the WebM and open it in a player that can decode VP9 or VP8 (the same browser is the safest bet). Verify duration, crop position, audio, and compatibility before deleting the original source.
Calculating the 1080 × 1920 Rectangle From Any Source
The four coordinates are constrained by the source frame, and the only arithmetic needed is to fit a 1080 × 1920 rectangle inside it. If the source already measures at least 1080 pixels wide and at least 1920 pixels tall, the crop rectangle can be placed anywhere inside. To center the crop, set X to half the difference between the source width and 1080, and Y to half the difference between the source height and 1920. The following worked example uses a 3840 × 2160 source, which is common for 4K screen recordings and exported edits.
Source width W_s = 3840, source height H_s = 2160. Target width W_t = 1080, target height H_t = 1920. X = (W_s − W_t) ÷ 2 = (3840 − 1080) ÷ 2 = 2760 ÷ 2 = 1380. Y = (H_s − H_t) ÷ 2 = (2160 − 1920) ÷ 2 = 240 ÷ 2 = 120. Rectangle: X = 1380, Y = 120, width = 1080, height = 1920.
Quick checks: X + width = 1380 + 1080 = 2460, which is ≤ 3840. Correct. Y + height = 120 + 1920 = 2040, which is ≤ 2160. Correct. Output area = 1080 × 1920 = 2,073,600 pixels, which is ≤ 3840 × 2160 = 8,294,400. Correct.
If the source is 1920 × 1080 (full HD landscape), the height is too short for a 1920-pixel crop, so the same formula gives a negative Y and the tool rejects the rectangle. In that case the source must be resized first or a different source with at least 1920 vertical pixels must be used; cropping cannot create pixels the source does not contain. Sources recorded natively for TikTok, such as 1080 × 1920 phone captures, can be cropped with the default rectangle (X = 0, Y = 0, width = 1080, height = 1920) and pass every check.
Real-Time Recording and WebM Output
Once the rectangle is accepted, the tool plays the source locally in the background, draws only the requested region into a Canvas at 30 fps using the WHATWG drawImage rule, and passes that canvas stream into a MediaRecorder. The recorder picks the first browser-reported WebM profile among VP9, VP8, and generic WebM, and the requested video bitrate is derived from the cropped pixel area at 30 fps, bounded from 180 kbps to 8 Mbps. This is a single-pass browser setting, not a guarantee of file size or visual quality, and fast motion, noise, grain, source codec, and browser encoder can change both.
Audio is appended only when the browser exposes a capturable track from the source. Support varies by browser, and the source may be audible during real-time processing, so plan on a quiet environment if the source is sensitive. The Matroska container that MediaRecorder produces can omit a finite duration, so the cropper runs a standards-tested WebM duration writer following the Matroska specification: it parses Segment Info and TimestampScale and inserts a big-endian Matroska Duration in timestamp-scale ticks, after which the result is checked for non-empty size and the requested dimensions. Object URLs, timers, recorder tracks, and source playback are released on replacement, error, stale completion, or unmount, so the tab does not leak memory between crops.
Review the WebM Before Posting
A few quick checks catch most issues before the clip reaches TikTok:
- Open the WebM in the same browser that recorded it and confirm the duration is finite and matches the source.
- Scrub to the start, middle, and end frames and confirm the crop rectangle sits where you expected; remember the tool does not track moving subjects, so if the subject moves the crop will reveal it.
- Confirm audio plays if the source had a sound. If the source had audio but the WebM is silent, the browser did not expose a capturable track; re-record with a browser that does, or extract the audio separately with the Video to Audio Converter and mux it back in.
- Confirm subtitles, chapters, rotation tags, HDR signaling, and color metadata are not present if TikTok expects a clean portrait clip; the crop pass does not preserve container features.
- Upload the WebM to TikTok and watch the first playback; if the platform re-encodes heavily, the cropper has still delivered the exact 1080 × 1920 frame the algorithm expects, so no extra padding or letterbox will appear.
For more on centering a 1080 × 1920 crop inside common phone and camera sources, see the guide on cropping a video for TikTok with exact pixel coordinates; the technique and constraints are the same, with extra worked examples for narrower source heights.