Resize video
In your browser, no upload
MP4
smaller picture · re-encoded
Video
MP4 · MOV · WebM → MP4Specification
8 rows| Item | Value | Notes |
|---|---|---|
| Input | Any video | MP4, MOV, WebM, AVI and more |
| Output | MP4, H.264 + AAC | Plays on phones, browsers and editors |
| Size | 1080p, 720p, 480p, 360p | By the short side; only sizes smaller than the video |
| Picture | Re-encoded as H.264 | x264, veryfast preset, CRF 23 |
| Sound | Copied | When it is AAC or MP3, else AAC 128 kbps |
| Time | Measured before it starts | A 2-second test encode on this device |
| Engine | This browser’s own encoder, or FFmpeg (16.8 MB) | FFmpeg is downloaded only when the browser cannot do the job, and only when you press the button that says so |
| Processed in | This browser | Not sent to a server |
What happens
5What happens, and why
Resizing a video draws every frame again at a smaller size and encodes it again. The result is smaller in pixels and, usually by much more, in bytes — half the width and half the height leaves a quarter of the pixels — which is why a video is usually resized: to get under a messenger’s or a form’s size limit, or to play smoothly on an older device.
The sizes are named by the short side: 1080p, 720p, 480p, 360p. A landscape 1920 × 1080 video becomes 1280 × 720 at 720p; a portrait phone video, 1080 × 1920, becomes 720 × 1280. Only sizes smaller than the video are offered, because enlarging adds pixels without adding detail. The picture comes out as H.264. The sound, when it is AAC or MP3, is copied without re-encoding — only the picture changes.
First the page asks the browser itself. Browsers carry the video encoders they use for calls and screen recording — H.264, VP9, AAC, Opus, often on the graphics chip — and when this browser can read your file and write the result with them, that is what happens: nothing is downloaded, the time is measured here first, and the line under the badge says the browser’s encoder did the work. MP4, MOV, WebM and MKV files usually qualify. AVI, WMV and FLV do not, and neither does an MP3, so those go the way below.
The work is done by FFmpeg, the program most video software is built on, compiled to WebAssembly so that it runs inside this page. It is large — 16.8 MB — and it is not downloaded until you press the button that says so. Then it reads your file, encodes 2 seconds from the middle of it as a test, and tells you how long the whole file will take on this device, before anything starts. That figure is measured here rather than taken from a table: the same engine and settings, your processor, your video. It is still an estimate, and it is labelled as one.
It is slower than a program installed on a computer. Here FFmpeg runs on one processor core, because a browser only lets a page use more when the site is served with particular security headers, and it cannot use the graphics chip’s video encoder at all. A long high-resolution video can take many minutes, and longer on a phone. The estimate says so before you commit to it, the progress line shows the time left as it goes, and Cancel stops it at once. When the browser’s own encoder can do the job, it is far quicker, and nothing is downloaded.
FAQ
5How much smaller will the file be
It depends on the video, so this page does not promise a figure. The size of the result is shown next to it before you download, beside the length and the time it took. To reach a particular file size — under a messenger’s or a mail service’s limit — use the Compress video page, which works backwards from the size you pick.
Can I pick an exact size
Not on this page. It offers the four standard sizes by the short side and keeps the shape of the picture; the exact size each gives is written on its button.
Does it lose quality
A little, as any re-encode does, and the badge says so. The picture is encoded with x264 at CRF 23, a constant-quality setting that spends bits where the picture needs them; at normal viewing most people cannot tell it from the source. What is lost is not recovered by converting back.
What if my phone runs out of memory
The page stops and says so, rather than handing back half a file. The video you drop is read from disk in pieces, never copied whole into memory, but the new file is built in memory until it is finished, so a long, high-resolution video can be too much for a phone. A shorter clip, a smaller size, or a computer will get through.
Is the video uploaded
No. The engine is downloaded to your browser, and your file is read and written there. There is no upload endpoint on this site, so there is nowhere for the video to go.