Is my video uploaded anywhere?

No. ffmpeg.wasm runs entirely inside your browser. The file stays on your device — nothing is transmitted to any server.

Does it work on mobile?

Yes. Works on iPhone Safari and Android Chrome without installing any app.

When should I use pad versus crop?

Use pad when preserving every part of the original is important — interviews, gameplay, captioned content. Use crop when the framing is flexible and you want a clean, edge-to-edge result for social feeds.

Does this re-encode the audio?

No. Only the video stream is re-encoded; audio is stream-copied. That keeps audio bit-perfect and makes encoding much faster.

Change Aspect Ratio

Letterbox, pillarbox, or fit a video to a new aspect ratio without distortion.

100% client-side · no upload

Video file (MP4, WebM, MOV…)

Settings Target aspect ratio Fitting mode

Load a file to begin.

How to use

Choose your video file. MP4 and WebM are best supported.
Select the target aspect ratio for the platform you are targeting (16:9 for YouTube, 9:16 for TikTok/Reels, 1:1 for Instagram feed).
Choose Pad to add black bars and keep the full picture, or Crop to fill the frame (may cut the edges). Click Change aspect ratio and download.

Related tools

More ways to use this tool

Frequently Asked Questions

Is my video uploaded anywhere?: No. ffmpeg.wasm runs entirely inside your browser. The file stays on your device — nothing is transmitted to any server.
Does it work on mobile?: Yes. Works on iPhone Safari and Android Chrome without installing any app.
When should I use pad versus crop?: Use pad when preserving every part of the original is important — interviews, gameplay, captioned content. Use crop when the framing is flexible and you want a clean, edge-to-edge result for social feeds.
Does this re-encode the audio?: No. Only the video stream is re-encoded; audio is stream-copied. That keeps audio bit-perfect and makes encoding much faster.

Last updated: 2026-05-20 By jarvisbox