Change Video Aspect Ratio (TikTok, Reels, Shorts)

A video filmed sideways does not fill a phone screen on TikTok, Instagram Reels or YouTube Shorts, and a phone video looks lost in a 16:9 player. This tool changes the shape of a video without stretching anything: the whole picture can sit on a blurred, enlarged copy of itself — the look most creators use — or on coloured bars, or be enlarged and cropped to fill the frame. It also makes square 1:1, 4:5 portrait and widescreen 16:9 versions. It runs in your browser with the ffmpeg engine (about 30 MB, downloaded once); nothing is uploaded.

How to use this tool

1. Pick the new shape: 9:16 for TikTok, Reels and Shorts, 1:1, 4:5, 16:9, 4:3 or your own.
2. Choose how to fill it: blurred background, coloured bars, or crop (with a position).
3. Pick the resolution and quality.
4. Choose the video, wait for the progress bar and download the MP4.

Formula

Fit: scale = min(W ÷ w, H ÷ h); crop: scale = max(W ÷ w, H ÷ h)

W × H is the new frame and w × h the video as players show it (rotation and non-square pixels taken into account). Fitting scales the picture until one side touches the frame, so all of it stays visible; cropping scales until both sides cover the frame and cuts the overflow at the chosen position. The blurred background is the same video, enlarged to cover the frame, blurred and slightly darkened.

Example

A 1920 × 1080 landscape clip made 9:16 (1080 × 1920): fitting gives a scale of min(1080 ÷ 1920, 1920 ÷ 1080) = 0.5625, so the picture becomes 1080 × 608 in the middle, with blurred video above and below. Cropping instead uses max(0.5625, 1.778) = 1.778: the picture becomes 3413 × 1920 and the central 1080 px of its width are kept — about a third of the original.

How long it takes

The whole video is re-encoded at the new size. Measured on a recent desktop computer with a 1080p source and the blurred background, the engine manages about 4 frames per second at 1080 × 1920 and about 7 at 720 × 1280, so a 30-second, 30 fps clip takes roughly 4 minutes at full resolution and 2 minutes at 720 px. Bars and cropping are a little faster.