Mastering WebP Animation with FFmpeg: A Step-by-Step Guide
Convert Video to Animated WebP Using FFmpeg with Auto-Cropping
Creating short, looping animations from video clips often involves using the GIF format. However, WebP offers a modern alternative with superior compression and quality. This tutorial demonstrates how to efficiently convert video segments into animated WebP images using FFmpeg, complete with automatic black bar cropping for seamless results.
Basic Video to WebP Conversion
The fundamental command for converting a video to a WebP animation is remarkably straightforward:
ffmpeg -i <in_file> -loop 1 -an -vf fps=fps=20 <out_file>The fps=fps=20 parameter (yes, the repetition is correct) sets the frame rate to 20 frames per second, striking a balance between animation smoothness and file size. This command creates a looping animation from the entire input video.
Clipping Video Segments
To target specific portions of a video, use the -ss (start time) and -to (end time) options:
ffmpeg -i <in_file> -ss <start_time> -to <end_time> -loop 1 -an -vf fps=fps=20 <out_file><start_time> and <end_time> can be either seconds (e.g., 10, 20) or timestamps (e.g., 00:01:17). For streamlined usage, let's encapsulate this in a Bash script:
#!/bin/bash
start=""
end=""
if [ ! -z "$2" ]; then
start="-ss $2"
fi
if [ ! -z "$3" ]; then
end="-to $3"
fi
ffmpeg -i "$1" $start $end -loop 1 -an -vf fps=fps=20 "$4"This script allows for easy command-line input of the input file, start time, end time, and output file name:
vid2webp infile.mp4 10 20 outfile.webpAutomatic Black Bar Cropping
To automatically detect and remove black bars, we leverage FFmpeg's cropdetect filter. This filter analyzes a sample of frames and determines optimal cropping dimensions.
crop=$(ffmpeg $start -i "$1" -vframes 10 -vf cropdetect -f null - 2>&1 | grep -m 1 -oP 'crop=\\[0-9:]+')The crop variable now contains the cropping dimensions (e.g., "640:360"). We extract the width and height values using the cut command:
width=$(echo "$crop" | cut -d':' -f1)
height=$(echo "$crop" | cut -d':' -f2)Next, we apply scaling to maintain aspect ratio while ensuring even dimensions for efficient processing. Bash lacks floating-point arithmetic, so we use bc:
scale=0.8
width=$(echo "$width * $scale" | bc)
height=$(echo "$height * $scale" | bc)
if [ "$height" -gt "$width" ]; then
scale="-2:$height"
else
scale="$width:-2"
fiFinally, we integrate the cropping and scaling parameters into the FFmpeg command:
ffmpeg -i "$1" $start $end -loop 1 -an -vf crop="$crop",scale="$scale",fps=fps="$fps" "$4"With this enhanced script, you can easily process multiple clips from a compilation video, generating perfectly cropped, looping WebP animations.
Example Usage
$ vid2webp infile.mp4 0 10 a.webp
$ vid2webp infile.mp4 10 18 b.webp
$ vid2webp infile.mp4 18 25 c.webpThis workflow streamlines the creation of high-quality, compact animated WebPs, ideal for various web applications. For a complete, robust version of this script, including error handling and advanced features, refer to the Github Repo.
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