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Javid Jamae
Javid Jamae

Posted on • Originally published at ffmpeg-micro.com

FFmpeg pad Filter: Letterbox and Pillarbox Video for Any Aspect Ratio

#ffmpeg #video #webdev #tutorial

Originally published at ffmpeg-micro.com

You have got a 4:3 video that needs to be 16:9. Or a landscape clip that needs to fit a 9:16 vertical frame. Scaling alone either distorts the image or leaves the wrong dimensions. FFmpeg's pad filter adds bars (black or any color) to fill the gap without touching a single pixel of your actual video.

Quick Answer: Pad to a Target Aspect Ratio

Letterbox a 4:3 video into a 16:9 frame with centered black bars:

ffmpeg -i input.mp4 -vf "scale=1920:1080:force_original_aspect_ratio=decrease,pad=1920:1080:(ow-iw)/2:(oh-ih)/2:black" output.mp4
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This first scales the video to fit inside 1920x1080 without distortion, then pads the remaining space with black. Two filters, one command.

How the pad Filter Works

The pad filter syntax:

pad=width:height:x:y:color
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  • width and height set the total canvas size
  • x and y position the video on that canvas
  • color fills the empty space (default is black)

Dynamic Centering with Expressions

Instead of hardcoding pixel values, use FFmpeg built-in variables:

ffmpeg -i input.mp4 -vf "pad=1920:1080:(ow-iw)/2:(oh-ih)/2:black" output.mp4
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  • ow = output width, oh = output height
  • iw = input width, ih = input height

This centers any input resolution on the target canvas.

Social Media Aspect Ratio Recipes

YouTube / landscape (16:9):

ffmpeg -i input.mp4 -vf "scale=1920:1080:force_original_aspect_ratio=decrease,pad=1920:1080:(ow-iw)/2:(oh-ih)/2:black" output.mp4
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Instagram Reels / TikTok / Shorts (9:16):

ffmpeg -i input.mp4 -vf "scale=1080:1920:force_original_aspect_ratio=decrease,pad=1080:1920:(ow-iw)/2:(oh-ih)/2:black" output.mp4
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Instagram square (1:1):

ffmpeg -i input.mp4 -vf "scale=1080:1080:force_original_aspect_ratio=decrease,pad=1080:1080:(ow-iw)/2:(oh-ih)/2:black" output.mp4
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Custom Bar Colors 

# White bars
ffmpeg -i input.mp4 -vf "pad=1920:1080:(ow-iw)/2:(oh-ih)/2:white" output.mp4

# Hex color (dark blue)
ffmpeg -i input.mp4 -vf "pad=1920:1080:(ow-iw)/2:(oh-ih)/2:0x1a1a2e" output.mp4
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Pad via the FFmpeg Micro API

If you are automating video processing in a pipeline, you can run the same pad filter through an API call:

curl -X POST https://api.ffmpeg-micro.com/v1/transcodes \
  -H "Authorization: Bearer YOUR_API_KEY" \
  -H "Content-Type: application/json" \
  -d '{ "inputs": [{"url": "https://example.com/video.mp4"}], "outputFormat": "mp4", "options": [{"option": "-vf", "argument": "scale=1080:1920:force_original_aspect_ratio=decrease,pad=1080:1920:(ow-iw)/2:(oh-ih)/2:black"}] }'
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Get a free API key at ffmpeg-micro.com to try it.

Common Pitfalls

  • Padding without scaling first causes errors if input is larger than pad dimensions
  • Odd dimensions break H.264/H.265 encoding
  • Using pad when you need crop: pad adds space, crop removes it

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