What is Video Aspect Ratio Changer?

A free tool to change your video's aspect ratio. Convert between 16:9 (landscape), 9:16 (portrait/TikTok), 4:3 (classic), 1:1 (Instagram square), and custom ratios. Choose crop, letterbox, or stretch modes — all processed privately on your device.

Conversions run through FFmpeg compiled to WebAssembly so the file never leaves your device. Pick a social-platform preset like TikTok or YouTube Shorts, or type any ratio (say 21:9 for cinemascope). Then choose how to fit: crop trims the edges, letterbox pads with a color you pick or a blurred copy of the source, stretch distorts to fill. Output resolution presets (480p, 720p, 1080p) let you downscale large clips before sharing.

How to use

1. Upload your video and select the target aspect ratio from the presets.
2. Choose a resize mode: crop (fill frame), letterbox (add a colored or blurred background), or stretch to fit.
3. Adjust the crop position if needed, preview the result, and download.

When to use

• Reframing a 16:9 webinar into a 9:16 vertical for TikTok or Reels.
• Producing 1:1 square cuts of product demos for Instagram feed posts.
• Fitting old 4:3 footage into a 16:9 timeline with clean letterbox bars.

Result

You recorded a 16:9 webinar and need a 1:1 square clip for Instagram. Upload the video, select 1:1, choose crop mode, drag to center the speaker in frame, and download the square version.

FAQ

Will changing the aspect ratio reduce my video quality?

A small loss is unavoidable because the video gets re-encoded. Pick a quality tier to control the trade-off: Quick makes a smaller file, Best stays near-lossless, Standard sits in the middle. If you crop heavily, the remaining area is scaled up — that part will look softer whichever tier you choose.

What's the difference between crop, letterbox, and stretch?

Crop fills the new frame and discards anything outside it. Letterbox keeps the entire image and pads the empty space with a color you pick — black by default, or white, brand colors, a custom hex, or a blurred copy of the video. Stretch resizes non-uniformly so faces and circles look distorted; useful rarely, mostly for memes.

Can I set a custom aspect ratio that isn't in the presets?

Yes. Pick the Custom Ratio option and type any two numbers, like 21 and 9 for ultrawide cinema or 5 and 4 for old computer monitors. The output keeps the original resolution along the longer axis.

What video formats are supported on input and output?

Input accepts MP4, WebM, and MOV. Output is MP4 (H.264 video, AAC audio), which plays on phones, on desktops, and in every editing app without extra codecs. Re-encoding to MP4 keeps the result compatible everywhere you might post or edit it.

Why does the position slider only work in crop mode?

In letterbox the whole image fits inside the frame, so there's nothing to reposition. Crop removes part of the picture, so the sliders pick which part survives. Centring on a speaker's face is the usual reason to touch them.

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