Ffmpeg

FFmpeg Skill

Process video and audio files using FFmpeg running inside a Docker container. Convert formats, extract audio, resize videos, create thumbnails, compress media, and more - all without installing FFmpeg locally.

Overview

This skill provides access to FFmpeg's powerful media processing capabilities through a containerized runtime. All processing happens inside an isolated Docker container with resource limits and no network access, ensuring security while maintaining full FFmpeg functionality.

When to Use This Skill

Use this skill when you need to:

• Convert video/audio between formats (MP4, WebM, AVI, MKV, MP3, WAV, etc.)
• Extract audio from video files
• Resize or scale videos to different resolutions
• Compress videos to reduce file size
• Create thumbnails from videos
• Trim or cut video clips
• Convert videos to animated GIFs
• Merge multiple video files
• Add or extract subtitles
• Adjust video bitrate and quality

Prerequisites

Docker

FFmpeg runs inside a Docker container, so Docker must be installed:

# macOS (using Homebrew)
brew install --cask docker

# Or download from: https://www.docker.com/products/docker-desktop

# Linux (Ubuntu/Debian)
sudo apt-get update
sudo apt-get install docker.io

# Start Docker service
sudo systemctl start docker
sudo systemctl enable docker

Verify Docker Installation

docker --version
docker ps  # Should list running containers

Configuration

Add to your .skill-engine.toml:

[skills.ffmpeg]
source = "docker:linuxserver/ffmpeg:latest"
runtime = "docker"
description = "FFmpeg video/audio processing"

[skills.ffmpeg.docker]
image = "linuxserver/ffmpeg:latest"
entrypoint = "ffmpeg"
volumes = ["${PWD}:/workdir"]
working_dir = "/workdir"
memory = "2g"
cpus = "4"
network = "none"
rm = true

Configuration Explained

• image: linuxserver/ffmpeg:latest - Official FFmpeg Docker image (~200MB)
• entrypoint: ffmpeg - Directly runs FFmpeg command
• volumes: ${PWD}:/workdir - Mounts current directory as /workdir in container
• working_dir: /workdir - Sets container working directory
• memory: 2g - Limits container to 2GB RAM
• cpus: 4 - Limits to 4 CPU cores
• network: none - Disables network access (processes local files only)
• rm: true - Automatically removes container after execution

Usage

FFmpeg skill uses pass-through syntax - all arguments after -- are passed directly to FFmpeg:

skill run ffmpeg -- [ffmpeg arguments]

All file paths are relative to your current directory, which is mounted as /workdir in the container.

Common Operations

Format Conversion

# MP4 to WebM
skill run ffmpeg -- -i input.mp4 output.webm

# AVI to MP4
skill run ffmpeg -- -i input.avi output.mp4

# MOV to MKV
skill run ffmpeg -- -i input.mov output.mkv

# Video to MP3 audio only
skill run ffmpeg -- -i video.mp4 -vn -acodec mp3 audio.mp3

Audio Operations

# Extract audio from video
skill run ffmpeg -- -i video.mp4 -vn audio.mp3

# Convert audio format
skill run ffmpeg -- -i audio.wav audio.mp3

# Adjust audio bitrate
skill run ffmpeg -- -i input.mp3 -b:a 192k output.mp3

# Merge audio and video
skill run ffmpeg -- -i video.mp4 -i audio.mp3 -c copy output.mp4

Video Resizing

# Resize to 1280x720 (720p)
skill run ffmpeg -- -i input.mp4 -vf scale=1280:720 output.mp4

# Resize to 1920x1080 (1080p)
skill run ffmpeg -- -i input.mp4 -vf scale=1920:1080 output.mp4

# Resize width to 640, maintain aspect ratio
skill run ffmpeg -- -i input.mp4 -vf scale=640:-1 output.mp4

# Resize height to 480, maintain aspect ratio
skill run ffmpeg -- -i input.mp4 -vf scale=-1:480 output.mp4

Video Compression

# Compress with CRF (Constant Rate Factor) - lower is higher quality
# CRF range: 0 (lossless) to 51 (worst), 23 is default, 18 is visually lossless
skill run ffmpeg -- -i input.mp4 -crf 28 output.mp4

# Compress with target bitrate
skill run ffmpeg -- -i input.mp4 -b:v 1M output.mp4

# Two-pass encoding for better quality at target size
skill run ffmpeg -- -i input.mp4 -b:v 1M -pass 1 -f mp4 /dev/null
skill run ffmpeg -- -i input.mp4 -b:v 1M -pass 2 output.mp4

Thumbnails & Images

# Extract single frame at 5 seconds
skill run ffmpeg -- -i video.mp4 -ss 00:00:05 -vframes 1 thumb.jpg

# Extract frame at specific time
skill run ffmpeg -- -i video.mp4 -ss 00:01:30 -vframes 1 frame.png

# Create thumbnail at 1/4 size
skill run ffmpeg -- -i video.mp4 -ss 00:00:05 -vf scale=iw/4:ih/4 -vframes 1 thumb.jpg

# Generate thumbnail every 10 seconds
skill run ffmpeg -- -i video.mp4 -vf fps=1/10 thumb%04d.jpg

GIF Creation

# Convert video to GIF
skill run ffmpeg -- -i input.mp4 output.gif

# High quality GIF with palette optimization
skill run ffmpeg -- -i input.mp4 -vf "fps=10,scale=320:-1:flags=lanczos,split[s0][s1];[s0]palettegen[p];[s1][p]paletteuse" output.gif

# Simple GIF with reduced frame rate and size
skill run ffmpeg -- -i input.mp4 -vf "fps=10,scale=320:-1" output.gif

Trim & Cut

# Trim from 10s to 40s (30 second clip)
skill run ffmpeg -- -i input.mp4 -ss 00:00:10 -t 00:00:30 output.mp4

# Trim from 1 minute to end
skill run ffmpeg -- -i input.mp4 -ss 00:01:00 -c copy output.mp4

# Cut first 10 seconds
skill run ffmpeg -- -i input.mp4 -ss 00:00:10 -c copy output.mp4

# Extract specific time range (from 5s to 15s)
skill run ffmpeg -- -i input.mp4 -ss 00:00:05 -to 00:00:15 -c copy output.mp4

Merge & Concatenate

# Create file list
echo "file 'video1.mp4'" > filelist.txt
echo "file 'video2.mp4'" >> filelist.txt
echo "file 'video3.mp4'" >> filelist.txt

# Concatenate videos
skill run ffmpeg -- -f concat -safe 0 -i filelist.txt -c copy merged.mp4

Rotate & Flip

# Rotate 90 degrees clockwise
skill run ffmpeg -- -i input.mp4 -vf "transpose=1" output.mp4

# Rotate 180 degrees
skill run ffmpeg -- -i input.mp4 -vf "transpose=2,transpose=2" output.mp4

# Flip horizontally
skill run ffmpeg -- -i input.mp4 -vf "hflip" output.mp4

# Flip vertically
skill run ffmpeg -- -i input.mp4 -vf "vflip" output.mp4

Speed Adjustment

# Speed up 2x (double speed)
skill run ffmpeg -- -i input.mp4 -vf "setpts=0.5*PTS" output.mp4

# Slow down 0.5x (half speed)
skill run ffmpeg -- -i input.mp4 -vf "setpts=2.0*PTS" output.mp4

Subtitles

# Add subtitle file
skill run ffmpeg -- -i video.mp4 -i subtitles.srt -c copy -c:s mov_text output.mp4

# Burn subtitles into video
skill run ffmpeg -- -i video.mp4 -vf subtitles=subtitles.srt output.mp4

# Extract subtitles
skill run ffmpeg -- -i video.mp4 -map 0:s:0 subtitles.srt

Advanced Examples

Batch Processing

# Convert all MP4 files to WebM
for file in *.mp4; do
  skill run ffmpeg -- -i "$file" "${file%.mp4}.webm"
done

# Create thumbnails for all videos
for file in *.mp4; do
  skill run ffmpeg -- -i "$file" -ss 00:00:05 -vframes 1 "${file%.mp4}.jpg"
done

Quality Presets

# High quality (larger file)
skill run ffmpeg -- -i input.mp4 -crf 18 -preset slow output.mp4

# Balanced quality/speed
skill run ffmpeg -- -i input.mp4 -crf 23 -preset medium output.mp4

# Fast encoding (lower quality)
skill run ffmpeg -- -i input.mp4 -crf 28 -preset fast output.mp4

# Very fast (lowest quality)
skill run ffmpeg -- -i input.mp4 -crf 28 -preset ultrafast output.mp4

Social Media Formats

# Instagram square (1:1, 1080x1080)
skill run ffmpeg -- -i input.mp4 -vf "scale=1080:1080:force_original_aspect_ratio=decrease,pad=1080:1080:(ow-iw)/2:(oh-ih)/2" -c:a copy instagram.mp4

# YouTube (1080p)
skill run ffmpeg -- -i input.mp4 -vf scale=1920:1080 -c:v libx264 -preset slow -crf 18 youtube.mp4

# Twitter (720p, under 512MB)
skill run ffmpeg -- -i input.mp4 -vf scale=1280:720 -b:v 2M twitter.mp4

File Paths

Working with Files

All file paths are relative to your current directory:

# Current directory files
cd /path/to/videos
skill run ffmpeg -- -i video.mp4 output.webm

# Subdirectory files
skill run ffmpeg -- -i input/video.mp4 output/video.webm

# Absolute paths NOT supported - use relative paths
cd /path/to/videos
skill run ffmpeg -- -i video.mp4 result.mp4  # ✓ Works
skill run ffmpeg -- -i /path/to/videos/video.mp4 result.mp4  # ✗ Won't work

Container Path Mapping

• Host: $PWD/video.mp4 → Container: /workdir/video.mp4
• Host: $PWD/input/file.mp4 → Container: /workdir/input/file.mp4

Supported Formats

Video Codecs

H.264 (MP4), H.265 (HEVC), VP8, VP9, AV1, MPEG-2, MPEG-4, Theora, DivX, Xvid

Audio Codecs

AAC, MP3, Opus, Vorbis, FLAC, WAV, AC3, DTS

Container Formats

MP4, WebM, MKV, AVI, MOV, FLV, 3GP, OGG, M4V, WMV

Security Features

Resource Limits

• Memory: 2GB limit prevents excessive RAM usage
• CPU: 4 cores max prevents CPU hogging
• Network: Disabled - no outbound connections
• Filesystem: Only current directory mounted (read/write)

Container Isolation

• Runs in isolated container namespace
• No access to host system files outside mounted directory
• Container auto-removed after execution
• No persistent container state

Performance Tips

1. Use appropriate presets:

   • ultrafast - Quick encoding, larger files
   • medium - Balanced (default)
   • slow - Better compression, slower
   • veryslow - Best compression, very slow

2. Copy streams when possible:

   skill run ffmpeg -- -i input.mp4 -c copy output.mp4  # No re-encoding
   

3. Hardware acceleration (if supported by image):

   skill run ffmpeg -- -hwaccel auto -i input.mp4 output.mp4
   

4. Batch process at once rather than multiple sequential runs

Troubleshooting

Docker Not Running

# Check Docker status
docker ps

# Start Docker Desktop (macOS)
open /Applications/Docker.app

# Start Docker service (Linux)
sudo systemctl start docker

Container Memory Issues

If processing large files, increase memory limit in .skill-engine.toml:

[skills.ffmpeg.docker]
memory = "4g"  # Increase to 4GB

File Not Found

Ensure you're in the correct directory:

# Check current directory
pwd
ls -la  # Verify files exist

# Change to correct directory
cd /path/to/videos
skill run ffmpeg -- -i video.mp4 output.webm

Permission Errors

Docker container may have permission issues:

# Check file permissions
ls -la video.mp4

# Make file readable
chmod 644 video.mp4

Common Errors

Docker Image Details

• Image: linuxserver/ffmpeg:latest
• Base: Alpine Linux
• Size: ~200MB
• Platforms: linux/amd64, linux/arm64, linux/arm/v7
• FFmpeg Version: Latest stable (6.x)
• Updates: Automatic with :latest tag

Resources

• FFmpeg Official Documentation
• FFmpeg Wiki
• Common FFmpeg Commands
• Video Codecs Guide
• Audio Encoding Guide

Examples Reference

Quick Reference Table

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