How to resize a video

Choose the video above. MP4, MOV, M4V, WebM and MKV open if your browser can decode the picture.
Under New size, pick a preset: 4K UHD 3840×2160, 1440p 2560×1440, 1080p 1920×1080, 720p 1280×720, 480p 854×480, 360p 640×360, vertical 1080×1920 or 720×1280, or square 1080×1080. Or type a width in pixels and the height follows the original shape.
If the preset's shape differs from your video's, a "Different shape" menu appears. Choose "Fit inside, add a background", "Fill the frame, crop the edges" or "Stretch (distorts)".
For Fit, pick the background: a blurred copy of the video, black or white.
Press "Resize video", keep the tab open, and download the MP4 when it is ready.

Three ways to handle a new shape

Take a 1920×1080 video going into a 1080×1080 square. The three options give very different results:

Fit inside, add a background: the whole picture is scaled to about 1080×608 and centred, with roughly 236 pixels of background above and below.
Fill the frame, crop the edges: the picture keeps its full 1080-pixel height and 420 pixels are cut from each side, so only the centre survives.
Stretch: all 1920 pixels of width are squeezed into 1080, so everything looks about 44% narrower. People and logos look visibly wrong.

Fit is the safe choice when every part of the frame matters: titles, slides, two people at opposite edges. Fill is right when the subject sits in the middle and the edges are scenery. Stretch is only useful for undoing an earlier mistake, such as a 4:3 recording that was saved as 16:9 and now looks too wide.

Add black bars, white bars or a blurred background

Bars above and below the picture are called letterboxing; bars at the sides are pillarboxing. The fit option adds whichever the shapes call for. A 1080×1920 phone video resized to 1920×1080, for example, becomes a 608×1080 picture in the middle with about 656 pixels of background on each side.

Black suits a TV, a projector or a cinema-style edit, where bars disappear into the dark surround.
White suits a video embedded in a bright slide or web page, where black bars would look like a hole.
A blurred copy suits social feeds: the frame is enlarged behind itself, softened and slightly darkened, so there is no flat dead space.

Resize, change resolution or crop?

This tool is for changing the frame's dimensions and, when needed, its shape. Nearby jobs have their own tools:

If the shape is already right and you only want fewer pixels, for example 4K to 1080p, change the video resolution. It works from the short side, so vertical and widescreen videos step down the same way. (When a preset here has the same shape as your video, this tool simply scales it too, and no shape menu appears.)
To decide exactly which part of the picture stays, crop the video with a draggable box; fill on this page always cuts equally from both sides.
For a landscape clip going to Shorts, Reels or TikTok, the horizontal to vertical converter lets you place the 9:16 window by hand.
For Instagram's feed, Reels and Stories sizes, use resize video for Instagram, which has those presets built in.
To hit a size in megabytes, compress the video instead. Resizing has no target file size; the file roughly follows the new pixel count.

Quality, sound and speed

Changing the frame size means every frame is decoded and encoded again. The tool uses the browser's WebCodecs encoder, writes an MP4 (H.264 when the browser offers it), and picks a bitrate from the new frame size and the source's own bitrate, so a downscaled video stays clean rather than being starved of data. Scaling up, such as 720p to 4K, makes a larger file with more pixels but no more detail. The soundtrack is copied as it was when MP4 can hold it. Dimensions are always even numbers, because encoders require them.

Speed depends on your device and the length of the video. Large results go to the browser's private storage where available; keep the tab open until the download appears.

Examples

A phone clip on a slide

A 1080×1920 clip goes into a 1920×1080 presentation. Fit with a white background, so the 608-pixel-wide picture sits on white that blends into the slide.

A widescreen trailer as a square post

A 1920×1080 trailer has titles across the full width. Fit into 1080×1080 with a blurred background keeps every word; fill would cut the first and last letters.

A 720p webinar for a vertical feed

Resizing 1280×720 to 720×1280 with fill enlarges the picture about 1.78 times and keeps only the centre, so the speaker looks softer. Fit on a blurred background keeps the original sharpness at a smaller size.

A TV that won't play 4K

A 3840×2160 drone clip is resized to 1920×1080. The shape matches, so it scales straight down with no bars and no cropping.

Limits

One size and one layout for the whole video; there is no scene-by-scene reframing.
Fill always keeps the centre. If the subject is off-centre, crop first, then resize.
A typed width keeps the original shape; to change the shape, use a preset.
The output is always MP4.
The browser must decode the source (HEVC depends on the device) and encode video through WebCodecs: a current Chrome or Edge, Safari 16.4 or later, or Firefox 130 or later on a computer.

Then add captions

A resized video for social media usually needs on-screen text. The free subtitle editor opens the MP4, shows a safe-area guide for 16:9, 9:16, 4:5, 1:1 and 4:3 frames, and renders the subtitles into a new video.

More free tools

Turn the file into text

Prefer one workspace for all mydubly tools? Open this tool in the dashboard · Browse every tool

Frequently asked questions

How do I add black bars to a video?

Choose a size with a different shape from your video, select "Fit inside, add a background" and set the background to Black. The whole picture is kept and bars fill the rest.

Can I type both a width and a height?

You can type a width, and the height is calculated from the original shape. For a different shape, pick one of the presets, or crop to the shape first and then resize.

Which part of the picture does Fill keep?

The centre. Fill cuts the same amount from both sides, or from the top and bottom, so an off-centre subject should be cropped by hand first.

Does resizing make the video file smaller?

Going to smaller dimensions usually gives a smaller file, because the bitrate follows the pixel count. If you need a specific size in MB, the compressor aims for that number directly.

Why don't I see the Different shape menu?

It only appears when the chosen size has a different shape from your video. If the shapes match, the video is scaled with no bars, cropping or stretching.

Will resizing a 1080p video to 4K make it sharper?

No. Upscaling creates more pixels from the ones that exist, so the file grows while the detail stays the same.

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