Local Processing · FFmpeg WASM · No Upload
Video Resizer
Change video dimensions with preset resolutions (1080p, 720p, 480p, 360p) or custom values — with optional aspect ratio lock. Processed entirely in your browser without uploading your video to a server.
video-resizer v2.0
1 Target resolution
Show resize log
Resize any video in four steps
Upload, pick dimensions, resize, download. Your video is processed locally in the browser.
Upload video
Drop a file up to 10 MB. It is read from a local object URL, never uploaded.
Pick dimensions
Choose a preset or enter custom values. Lock aspect ratio to avoid stretching.
Resize
FFmpeg's scale filter resamples every frame at the new resolution.
Download
Preview the resized result and download the MP4 file.
Precision, privacy, and predictability
What the resizer does with your video — and what it deliberately does not.
Zero upload
FFmpeg WASM runs in a worker inside your browser. Your uploaded video is processed locally and is not sent to a video-processing server.
Aspect ratio lock
When enabled, height is auto-calculated from the width using the original ratio — and rounded to an even number for H.264 compatibility.
Honest sizing
Presets larger than the original are disabled because upscaling cannot restore detail that is not present in the source. Custom dimensions can still be used when a larger output is required.
Common video resolutions
What each resolution means in practical terms.
1080p
1920 × 1080 — Full HD resolution for detailed playback and larger displays.
720p
1280 × 720 — HD resolution that uses fewer pixels than 1080p.
480p
854 × 480 — SD resolution suitable when a smaller frame is needed.
360p
640 × 360 — Lower-resolution output for situations where smaller dimensions are preferred.
What it does, and what it does not
Clear boundaries so you know when to reach for another tool.
What it does
- Downscale any browser-decodable video up to 10 MB.
- 5 presets (1080p → 360p) plus custom width/height.
- Aspect ratio lock for distortion-free resizing.
- Smart even-number rounding for H.264 compatibility.
- Export MP4 with H.264 video, AAC audio, and the faststart flag.
- Process videos locally after the FFmpeg engine has loaded.
What it does not
- Magic upscale quality — upscaling cannot invent detail.
- Handle files above 10 MB — browser memory is the ceiling.
- Rotate, crop, or change speed (use dedicated tools).
- Output formats other than MP4 in this tool.
Common issues and fixes
Quick answers to common Video Resizer problems.
Engine won't load
The FFmpeg WASM engine needs WebAssembly and Web Workers, and its files must not be blocked. Exclude ffmpeg from JS minify/combine/delay in optimisation plugins, or self-host the engine files.
Resize fails on long videos
Re-encoding happens in browser memory. Near the 10 MB cap or with long durations, expect more failures. Use a desktop tool for heavy jobs.
Output looks softer than the original
Downscaling always loses some detail — that is physics. To preserve quality, use the smallest reduction that still fits your use case.
Height is 1 px off
The lock rounds the calculated height to an even number for the encoding path. A 1 px difference is normally negligible in playback.
Frequently asked questions
Honest answers about the Video Resizer.
Is my video uploaded to a server?
No. The FFmpeg WASM engine runs entirely in your browser. Your video is read from a local object URL, resized in memory, and never transmitted to AllInOneTools or any third party.
What does Lock Aspect Ratio do?
When enabled, changing the width automatically calculates the height so the original proportions are preserved. This prevents the video from looking stretched or squashed.
Why are some sizes grayed out?
Preset buttons larger than the original video are disabled — upscaling a small video does not add detail and often produces worse results than keeping the original size.
Why is the output height sometimes slightly different from what I typed?
When aspect ratio is locked, the tool rounds the calculated dimensions to even numbers for the H.264/yuv420p encoding path, so the result may differ by 1 pixel.
What is the output format?
MP4 with H.264 video and AAC audio, plus the faststart flag for smooth web playback. The resized video keeps the original duration and audio.
Why is there a 10 MB limit?
Re-encoding happens entirely in browser memory. The 10 MB input limit helps reduce memory pressure, especially on devices with limited resources. For larger files, use a desktop tool like ffmpeg, HandBrake or Shutter Encoder.