To crop a video for TikTok, you select an exact rectangular region inside the source frame using whole-pixel X, Y, width, and height values measured from the top-left corner, then re-record only that region as a WebM. TikTok's primary vertical frame is 1080 × 1920 pixels (a 9:16 aspect ratio), so the crop rectangle usually needs to match those numbers exactly when the goal is a full-screen vertical post. The Video Cropper tool applies one fixed rectangle to every frame of the source, draws only the requested pixels into a Canvas, and records that Canvas stream in real time using the browser's MediaRecorder. No upload is involved, which means the source file stays on the device and the only file that leaves the tab is the cropped WebM you choose to download. Because recording happens in real time at the source's natural playback speed, a one-minute source takes roughly one minute to process, and the tab must stay open until the download link appears.
What "Crop for TikTok" Means in Pixel Terms
Cropping is not the same as resizing. Resizing changes how many pixels make up each frame while keeping the entire visible image in view; cropping selects which part of the existing frame survives. Video Cropper does the second job. It does not analyze the scene, follow a moving subject, or guess where the action is. It takes the four numbers you type and applies them to every frame, exactly the same way, for the whole clip. That is why the inputs are called X, Y, width, and height instead of "start time" or "zoom level". When the goal is a TikTok post, the most useful application is removing unwanted edges from a wider source (letterbox bars, a tripod shadow, dead space above a head) so the remaining rectangle matches the platform's expected frame.
When the source already has the right aspect ratio, you can usually leave the defaults in place and skip cropping entirely. The defaults select the full frame. The reason cropping matters is that most footage arrives with the wrong shape: a 16:9 horizontal clip from a camera, a 4:3 export from older software, or a phone clip shot sideways. The Video Cropper tool cannot add pixels that are not already in the source, but it can pick exactly the pixels you want to keep.
TikTok's Common Frame Sizes
A few TikTok-compatible frames cover the vast majority of posts. The exact specifications change occasionally, but the table below lists the dimensions people target most often when they want a clean full-screen result, a square post, or a shorter portrait that still looks right in the feed.
| Use case | Aspect ratio | Target resolution |
|---|---|---|
| Full-screen vertical (default feed) | 9:16 | 1080 × 1920 |
| Square post | 1:1 | 1080 × 1080 |
| Tall portrait | 4:5 | 1080 × 1350 |
These are the rectangles the source needs to expose before you crop. If the source's decoded dimensions are smaller than the target frame, the output cannot reach those pixels because cropping only ever removes outer area. For example, a 1920 × 1080 source has only 1080 vertical pixels, so a 1080 × 1920 vertical crop is impossible from that source without first upscaling, and Video Cropper does not upscale.
For a TikTok post pulled from a wide landscape clip, the practical move is to choose a target that fits inside the source's smallest side and matches an aspect ratio the platform accepts. When the source is 1920 × 1080, the largest 9:16 rectangle that fits is 608 × 1080 (9:16 rounded to whole pixels), centered at X = 656. That is enough to post vertically with safe margins when the subject sits in the middle of the frame.
Crop a Video for TikTok With Video Cropper
The tool runs entirely in the browser tab. Follow the steps below to crop a local video for TikTok without uploading the source.
- Open the Video Cropper tool in your browser.
- Choose a browser-decodable video file (MP4, WebM, MOV, M4V, or Ogg). An accepted extension does not guarantee codec support, so decoding depends on the current browser. The source may not exceed 500 MiB, five minutes of decoded duration, 4096 px on any side, or 3840 × 2160 of total area.
- Wait for the source dimensions to appear. The tool reads the decoded width and height of the first frame, and the four coordinate inputs become usable only after that value is known.
- Type the X offset (pixels from the left), Y offset (pixels from the top), width (horizontal extent), and height (vertical extent) of the rectangle you want to keep. Every value is an untrimmed nonnegative whole pixel; width and height must each be at least two; X + width and Y + height must stay inside the decoded source; and the resulting output area cannot exceed 3840 × 2160.
- Select Crop video. The tab plays the source locally, draws only the requested region into a Canvas at 30 fps, captures that Canvas as a WebM, and appends the source's audio track when the browser exposes one through media capture.
- Keep the tab open and focused for the full duration of the recording. A one-minute source takes about one minute; longer sources take proportionally longer. Closing or backgrounding the tab mid-recording can interrupt the stream and produce a partial file.
- When the download link appears, save the WebM and review it end to end before deleting the source. Confirm duration, the cropped rectangle, audio presence, and that the file plays in the destination player.
Reading the X, Y, Width, and Height Inputs
The four inputs describe a static rectangle in the source's coordinate system, not a region of interest or a timeline. X and Y are offsets measured from the top-left corner of every frame: X moves the rectangle right and Y moves it down. Width is the horizontal extent and height is the vertical extent. The four values together define one rectangle that the tool applies to every frame in the clip.
A few rules keep the input safe. Each value must be an untrimmed nonnegative whole number, and the tool does not round or shift invalid input. Width and height must each be at least two pixels because a one-pixel or zero-pixel dimension has nothing meaningful to record. X + width must not exceed the source's decoded width, and Y + height must not exceed the source's decoded height, so the rectangle stays entirely inside the source. The output area (width × height) cannot exceed 3840 × 2160 pixels, and larger rectangles fail without producing a partial file.
Defaults select the full frame, which is a useful way to test the pipeline before locking in a smaller crop. When the goal is to extract the center of a 1920 × 1080 source as a 9:16 vertical post, the math is width = round(1080 × 9 ÷ 16) = 608, then X = (1920 − 608) ÷ 2 = 656. The four inputs become X = 656, Y = 0, width = 608, height = 1080. That rectangle is fully inside the source, every value is a whole pixel, and the output area of 608 × 1080 = 656 640 pixels sits well under the 3840 × 2160 ceiling.
The crop does not move over time. It is not a tracking crop, a pan, or a zoom. If the subject drifts across the frame, every frame receives the same fixed rectangle, so place the rectangle where the subject spends most of its time.
Limits That Decide Whether the Crop Will Finish
A few hard limits decide whether the recording runs to completion. The browser-decoded file must satisfy the input budget, and the requested rectangle must satisfy the output budget. Both sets of checks happen before recording starts, and an invalid input fails immediately without producing a partial file.
| Constraint | Limit |
|---|---|
| Source file size | Positive file, up to 500 MiB |
| Decoded duration | Above zero, no more than 5 minutes |
| Source side | No side above 4096 pixels |
| Source area | No larger than 3840 × 2160 pixels |
| Output area | No larger than 3840 × 2160 pixels |
| Width / height | At least 2 pixels each |
| Offset (X, Y) | Nonnegative whole pixels, with X + width and Y + height inside the source |
| Processing time | Real time at source playback speed; tab must stay open |
These limits share the same audited gates used by the Video Compressor. If the source is too large, too long, or has too many pixels, the crop cannot start. If the rectangle is invalid, the crop cannot start. If the source's audio cannot be captured through the browser's media capture pipeline, the recording runs without sound and the output is silent.
The output bitrate scales with the cropped area at 30 frames per second and is bounded between 180 kbps and 8 Mbps. That is a single-pass browser setting, not a guarantee of file size or visual quality. Fast motion, noise, grain, the source codec, and the browser's encoder all change the actual size of the WebM. Keep the original file until the entire output has been reviewed.
Before You Upload the Cropped WebM to TikTok
Three quick checks catch most issues before the file reaches the upload screen.
First, play the WebM in the same player you plan to use on desktop or mobile. Confirm the duration matches the source, the cropped rectangle sits exactly where you expected, and the file decodes without errors. The output uses the first browser-reported WebM recorder among VP9, VP8, and generic WebM, and the tool writes a finite Matroska Duration value in timestamp-scale ticks so the file reports a real duration rather than an open-ended stream, per the Matroska container specification. The result must remain nonempty and decode at the requested dimensions, but some players still disagree on edge cases.
Second, verify the audio. Audio is included only when the browser exposes a capturable track through media capture. Support varies by browser and by source codec. When the source had sound and the output is silent, re-run the crop with a different source codec or convert the source so the current browser exposes an audio track through capture.
Third, expect metadata loss. Subtitles, chapters, attachments, rotation tags, HDR signaling, and most color metadata are not preserved by the crop. If the source relies on a rotation tag to display correctly, the rotation tag will be gone in the WebM. The crop changes the visible frame region and nothing else; it is not a trim-by-time, resize, compress-only, redact, blur, or object-removal tool. When a different kind of change is needed, pair the crop with a tool that targets that change, such as Video Trimmer for cutting by time, the Video Resizer for aspect-preserving resizing, or the Video Compressor for smaller file size at the same rectangle.
When you want to crop a video for a different platform with the same pixel-precise approach, the workflow carries over. The same pixel-coordinate method is used for Instagram posts and Stories.