Video Resize
Change the dimensions of a video while maintaining the aspect ratio
Change a Video's Pixel Dimensions Without Cropping It
This tool changes a video's width using ffmpeg's scale filter set to scale=width:-2:flags=lanczos. The -2 tells ffmpeg to compute the height automatically from the new width while keeping the original aspect ratio, and rounding to the nearest even number, which matters because H.264 requires even dimensions to encode correctly. The flags=lanczos part picks a specific resampling algorithm: Lanczos uses a sinc-based kernel that generally holds onto more edge detail when shrinking an image than a plain bilinear resize, which is the more common default in simpler tools.
Five resolution presets (4K, 1080p, 720p, 480p, 360p) are provided as quick width targets, or you can drag the slider for any custom width between 160 and 3840 pixels. The output can be re-encoded as MP4 (H.264/AAC) or WebM (VP9/Opus), and the whole operation happens through ffmpeg.wasm in the browser tab, no part of the video is transmitted anywhere. This is the tool to reach for when a 4K download is overkill for where it's going, or when a platform expects a specific pixel width and your source footage doesn't match it.
How to Use
- 1
Upload a video file
MP4, WebM, MOV, and AVI containers are all accepted.
- 2
Pick a resolution preset or drag the width slider
4K, 1080p, 720p, 480p, and 360p presets set the width directly, or choose any custom value from 160px up to 3840px.
- 3
Choose the output format
MP4 (H.264) for broad compatibility, or WebM (VP9) if the destination is a modern browser or web embed.
- 4
Resize and compare
Height is computed automatically from the new width to preserve aspect ratio, then the video is re-encoded at the target size.
- 5
Download the result
Check the before/after file size, then save the resized video to your device.
Key Features
- →The scale filter here uses Lanczos resampling, which tends to preserve more detail on downscales than the bilinear resizing many basic tools use by default.
- →Height is always derived from width to preserve the original aspect ratio; there's no independent height control, so the output never stretches or squashes the frame.
- →Cutting width in roughly half (1080p to 720p, for instance) reduces the total pixel count to about a quarter, which is why resizing alone can meaningfully shrink file size.
- →Downscaling a 4K download to 1080p is a common move before sharing footage that was only shot in 4K for editing flexibility.
- →If you need a smaller file with the same resolution, use the Video Optimize tool instead, resizing changes dimensions, not compression level.
- →WebM (VP9) output is usually a bit smaller than MP4 at a similar visual quality, but MP4 remains the safer choice for older devices and editing software.
Frequently Asked Questions
Why does the tool only let me set width, not height directly?
The underlying ffmpeg command uses scale=width:-2, where -2 tells ffmpeg to calculate the height automatically from the new width so the aspect ratio never distorts, and to round to an even number since H.264 requires even dimensions.
What does the Lanczos scaling actually change about the result?
It's the resampling algorithm ffmpeg uses when computing new pixel values during the resize. Lanczos uses a sinc-based kernel that tends to retain sharper edges than simpler bilinear resizing, which matters most when scaling down significantly.
Will resizing distort or crop my video?
No. Since height is derived proportionally from the new width, the full frame is preserved at the new size with the same aspect ratio, nothing is cropped or stretched.
Does a smaller resolution always mean a smaller file?
In almost all cases yes, since fewer pixels per frame means less data for the encoder to compress, but the exact reduction depends on the CRF/bitrate settings used during re-encoding as well.
What's the largest width I can resize up to?
The slider goes up to 3840px (4K width), but resizing only ever works with the resolution already present in your source file, it won't add detail beyond what the original video actually captured.
Last updated: June 2026