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Video Resizer

Resize a local video to a bounded exact or aspect-preserving WebM without uploading the source.

Privacy: your files never leave your device. All processing happens locally in your browser.

How to use

  1. 1.Choose one supported local video and wait for browser metadata to load.
  2. 2.Enter maximum width and height, then choose aspect-preserving Fit or exact Stretch.
  3. 3.Select Resize video, keep the tab open during real-time encoding, and download the WebM result.

About Video Resizer

Video Resizer changes the pixel dimensions of a local video without uploading it. Choose a supported file, enter a maximum width and height, then select Fit to preserve the source aspect ratio or Stretch to produce the exact requested dimensions. The output is a downloadable WebM created in the current browser tab.

Fit mode treats the entered dimensions as a bounding box. It applies the smaller width or height scale, preserves the source ratio, and never crops. Stretch mode uses the requested width and height independently, so it can intentionally distort the picture. Output dimensions are made even because common browser video encoders are more reliable with codec-safe even pixel sizes.

Each dimension must be a whole number from 2 to 1920 pixels. The source can be up to 500 MiB and five minutes, no more than 4096 pixels per side, and no greater than 3840 × 2160 pixels in area. Eight independent geometry fixtures cover landscape, portrait, square, same-ratio, bounding-box, stretch, and odd-dimension cases.

The browser decodes the source, draws frames onto a resized canvas, captures that canvas at up to 30 frames per second, and adds any browser-exposed audio tracks. MediaRecorder selects a supported VP9 or VP8 WebM configuration. This is a real-time re-encode, not a metadata-only dimension change, so processing normally takes about as long as the video.

Quality, bitrate, frame timing, audio layout, color metadata, and file size can differ from the source. The generated WebM receives a finite duration through the shared audited Matroska duration writer. Unsupported codecs, invalid dimensions, excessive source metadata, empty recorder output, and browser capability gaps fail visibly instead of creating a misleading download.

The tool does not upscale detail, remove black bars, crop a subject, preserve subtitles or multiple tracks, bypass DRM, or promise professional mastering. Use only media you own or may edit. For frame-accurate delivery, long footage, required MP4 output, color-managed workflows, or exact bitrate control, use a dedicated desktop encoder.

Methodology & sources

Validate bounded local video metadata and integer target dimensions, calculate either contain-style aspect-preserving geometry or exact stretch geometry, round dimensions to positive even values, draw decoded frames to a canvas at 30 fps, attach available audio tracks, record the captured canvas using a supported VP9/VP8 WebM codec and bounded bitrate, reject empty output, patch the finite duration, and expose a revocable local download URL.

Frequently asked questions

Is the video uploaded?
No. Decode, canvas resizing, recording, and download generation happen in the current browser tab.
What is the difference between Fit and Stretch?
Fit preserves aspect ratio inside the requested box. Stretch uses the exact width and height and can distort the picture.
Why is the result WebM?
The tool uses built-in browser codecs and avoids a large media dependency or server processing.
Why are odd dimensions reduced by one pixel?
Even dimensions are more reliable with common browser video encoders, so odd values are rounded down safely.

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