How to use Video Resizer
- 1Drop in a video file
- 2Enter the width you want in pixels
- 3The height is calculated to preserve the aspect ratio
- 4Choose a quality level for the re-encode
- 5Download the resized MP4
What Video Resizer does
Resolution is the most effective lever on video file size, and the one people reach for last. Halving the width quarters the pixel count, and the bitrate needed to hold a given quality falls with it. Dropping a 4K clip to 1080p usually shrinks it more than any amount of quality tuning at the original size, and looks better than a heavily compressed 4K file.
The constraint is that H.264 encodes in blocks and requires even pixel dimensions. That is why you set only the width here: the height is derived from the aspect ratio and then rounded to the nearest even number. A one-pixel adjustment nobody can see is preferable to an encode that refuses to start.
When to use it
- 4K footage nobody will watch in 4K
- Phones and cameras default to the highest resolution they support. For anything destined for a chat app or a web page, 1080p or 720p is indistinguishable and a fraction of the size.
- Video for a web page
- A background or inline video only needs enough pixels for the space it occupies. Serving 4K into a 600-pixel-wide element wastes bandwidth on every visitor.
- Getting under an upload limit
- When compression alone will not fit, reducing the resolution usually will — and a smaller video at good quality looks better than a large one compressed hard.
- Matching clips before editing
- Footage from several devices at several resolutions is easier to work with once everything is the same size.
Video Resizer settings explained
- Width
- The output width in pixels, minimum 16. Common targets are 1920 for full HD, 1280 for 720p and 854 for 480p. This is the only dimension you set.
- Automatic height
- Calculated from the source aspect ratio so the video is never stretched, then rounded to the nearest even number. H.264 encodes in even-sized blocks and rejects odd dimensions outright.
- Quality level
- High (CRF 22), Balanced (CRF 27) or Smallest file (CRF 32). Resizing already reduces the data substantially, so a higher quality setting costs less here than it would at full resolution.
- Audio re-encoding
- The audio is converted to AAC rather than copied, because the source track may be in a codec — Opus or Vorbis, for instance — that an MP4 container cannot legally hold.
Common target widths
| Width | Name | Pixels vs 4K | Typical use |
|---|---|---|---|
| 3840 | 4K | 100% | Archival, large-screen viewing |
| 1920 | 1080p | 25% | The sensible default for most uses |
| 1280 | 720p | 11% | Web embedding, messaging |
| 854 | 480p | 5% | Tight size limits, previews |
Limits and what to expect
- Only the width is settable; the height always follows the source aspect ratio.
- Height is rounded to an even number, so the result can differ by one pixel from the exact ratio.
- Enlarging is possible but pointless — no detail can be added that was not captured.
- Output is always MP4 with H.264 and AAC, whatever the input format was.
- Encoding is single-threaded and runs on your device, so a long video takes minutes.
Troubleshooting
- The height is one pixel off what I calculated
- H.264 requires even dimensions, so the derived height is rounded to the nearest even number. The difference is a single pixel and cannot be seen; without it the encoder would refuse to start.
- The resized video looks soft
- Reducing resolution removes detail permanently — that is what it does. If it looks softer than expected, the quality level may also be low. Try High quality at the same size before assuming the resolution is the problem.
- The file did not shrink as much as I expected
- Quality is held at the CRF target rather than the bitrate, so a detailed or fast-moving clip still spends what it needs. Combine a smaller width with Smallest file mode if you need a specific size.
- It is taking a long time
- Every frame is decoded, scaled and re-encoded on a single thread in your browser. Trim the clip to just the part you need first — trimming is a stream copy and takes seconds.
Your files and your privacy
Scaling and encoding both run through an ffmpeg build compiled to WebAssembly inside your browser tab. The video is never uploaded and no copy is written to a server. The only network request is for the engine itself, which is generic and carries nothing of yours.
What to use next
FAQ
Why can I only set the width?
Because the height is derived from it to keep the aspect ratio, which prevents the video from being stretched. Setting both independently would make distortion the default outcome rather than something you have to ask for.
Why is my output height an even number?
H.264 encodes in blocks of even pixel dimensions and rejects odd ones. The calculated height is rounded to the nearest even value — a one-pixel change nobody can see, and the alternative is an encode that will not run.
Does resizing reduce quality?
Reducing the resolution permanently discards detail, so yes in that sense. But at a sensible target it usually looks better than the alternative: a heavily compressed video at the original size shows blocking artefacts that a cleanly encoded smaller one does not.
What resolution should I choose?
1920 wide (1080p) for most purposes — it is indistinguishable from 4K on a phone or a laptop and a quarter of the pixels. 1280 (720p) for web embedding and messaging. Only stay at 4K if the video will actually be watched on a large screen.
Can I make a video larger?
You can enter a bigger width, but nothing is gained. Upscaling interpolates pixels that were never captured, so the result is a larger file that looks softer than the original.
Is my video uploaded?
No. Scaling and encoding happen inside your browser on your own device, with nothing transmitted at any point.