What is the difference between crop and letterbox/pillarbox?

Crop removes pixels from the edges of the frame to fit the new ratio — content at the edges is lost. Letterbox (horizontal bars) or pillarbox (vertical bars) adds black padding to fill the unused area — the full original frame is preserved but black bars appear.

Which method should I choose?

Use crop when you want a clean edge-to-edge result and can afford to lose some frame edges. Use letterbox/pillarbox when preserving the full original frame matters — common for archiving or when the subject is centered.

Why must dimensions be even numbers?

H.264 and H.265 encoders require both width and height to be divisible by 2. The tool rounds calculated values up to the nearest even number automatically.

Do I need to install anything?

No. The dimension calculator runs in your browser. To actually re-encode the video you will need FFmpeg installed. The tool provides the exact FFmpeg command to copy and run.

What does the crop offset represent?

The offset is the number of pixels from the top-left corner where the crop window starts. A centered crop splits excess pixels equally on both sides.

Video Aspect Ratio Changer

Calculate output dimensions when changing a video's aspect ratio — crop or letterbox/pillarbox — for any common ratio.

Source Video

Width (px)

Height (px)

Source ratio: 16:9

Target Aspect Ratio

Method

Visual Preview

Source

1920×1080

Output

—

Output Dimensions

Output Width

1920

Output Height

1080

FFmpeg Command

ffmpeg -i input.mp4 -vf "crop=1920:1080:0:0" -c:a copy output.mp4

Copied!

Summary

Enter your source video dimensions and pick a target aspect ratio to instantly see the correct output dimensions for both crop and letterbox/pillarbox methods. The tool shows exactly how many pixels are added or removed, and generates an FFmpeg command you can paste directly into your terminal. All math runs in your browser — no file upload needed.

How it works

Enter the width and height of your source video (e.g. 1920 x 1080).
Select a target aspect ratio preset or type a custom ratio (e.g. 3:2).
Choose whether to crop the video or add letterbox/pillarbox bars.
The tool shows the exact output dimensions and the offset for centered crop or bar size.
Copy the generated FFmpeg command and run it in your terminal.

Use cases

Convert a 16:9 landscape video to 9:16 for Instagram Reels or TikTok.
Add letterbox bars to a 21:9 video to fit a 16:9 container.
Crop a 4:3 archive recording to 16:9 for modern widescreen display.
Prepare a 1:1 square version of a video for Instagram feed posts.
Calculate pillarbox padding when placing a 4:3 source inside a 16:9 container.
Find the exact crop offset to keep a subject centered after ratio change.

Frequently Asked Questions

Last updated: 2026-06-13 · Reviewed by Nham Vu