Resize a Video

Leave the aspect-ratio box ticked and set only the width; the height is worked out for you. Untick it to force an exact width and height.

An MP4 (H.264 video, AAC audio). This works best in Chrome, Edge and Firefox; Safari’s video encoding support is more limited.

Usually yes — fewer pixels per frame means less data to encode, so scaling 4K down to 1080p typically cuts the file substantially. It isn't guaranteed, because the final size also depends on the encoder's bitrate, but for the common case of shrinking a clip to fit an upload limit or email attachment, reducing the dimensions is the most effective single lever. If size is the whole goal, resize down and you'll almost always land smaller.

You can enter dimensions bigger than the source and it will re-encode to that size, but upscaling doesn't create detail that wasn't captured — a 720p clip stretched to 1080p is still 720p worth of information in a larger frame, and can look soft. Enlarging is worth it only when a platform demands a minimum resolution; for image quality, staying at or below the original dimensions is better.

Resizing requires a re-encode — the frames are decoded, scaled and encoded again — so it's not a lossless copy. The tool encodes at a quality high enough that a single pass is hard to tell from the source, but re-encoding the same file over and over will slowly soften it, as any lossy format does. Resize once from your best original rather than resizing an already-resized copy.