media-processing（媒体处理）

Media Processing Skill

Process video, audio, and images using FFmpeg and ImageMagick command-line tools for conversion, optimization, streaming, and manipulation tasks.

When to Use This Skill

Use when:

• Converting media formats (video, audio, images)
• Encoding video with codecs (H.264, H.265, VP9, AV1)
• Processing images (resize, crop, effects, watermarks)
• Extracting audio from video
• Creating streaming manifests (HLS/DASH)
• Generating thumbnails and previews
• Batch processing media files
• Optimizing file sizes and quality
• Applying filters and effects
• Creating composite images or videos

Tool Selection Guide

FFmpeg: Video/Audio Processing

Use FFmpeg for:

• Video encoding, conversion, transcoding
• Audio extraction, conversion, mixing
• Live streaming (RTMP, HLS, DASH)
• Video filters (scale, crop, rotate, overlay)
• Hardware-accelerated encoding
• Media file inspection (ffprobe)
• Frame extraction, concatenation
• Codec selection and optimization

ImageMagick: Image Processing

Use ImageMagick for:

• Image format conversion (PNG, JPEG, WebP, GIF)
• Resizing, cropping, transformations
• Batch image processing (mogrify)
• Visual effects (blur, sharpen, sepia)
• Text overlays and watermarks
• Image composition and montages
• Color adjustments, filters
• Thumbnail generation

Decision Matrix

Installation

macOS

brew install ffmpeg imagemagick

Ubuntu/Debian

sudo apt-get install ffmpeg imagemagick

Windows

# Using winget
winget install ffmpeg
winget install ImageMagick.ImageMagick

# Or download binaries
# FFmpeg: https://ffmpeg.org/download.html
# ImageMagick: https://imagemagick.org/script/download.php

Verify Installation

ffmpeg -version
ffprobe -version
magick -version
# or
convert -version

Quick Start Examples

Video Conversion

# Convert format (copy streams, fast)
ffmpeg -i input.mkv -c copy output.mp4

# Re-encode with H.264
ffmpeg -i input.avi -c:v libx264 -crf 22 -c:a aac output.mp4

# Resize video to 720p
ffmpeg -i input.mp4 -vf scale=-1:720 -c:a copy output.mp4

Audio Extraction

# Extract audio (no re-encoding)
ffmpeg -i video.mp4 -vn -c:a copy audio.m4a

# Convert to MP3
ffmpeg -i video.mp4 -vn -q:a 0 audio.mp3

Image Processing

# Convert format
magick input.png output.jpg

# Resize maintaining aspect ratio
magick input.jpg -resize 800x600 output.jpg

# Create square thumbnail
magick input.jpg -resize 200x200^ -gravity center -extent 200x200 thumb.jpg

Batch Image Resize

# Resize all JPEGs to 800px width
mogrify -resize 800x -quality 85 *.jpg

# Output to separate directory
mogrify -path ./output -resize 800x600 *.jpg

Video Thumbnail

# Extract frame at 5 seconds
ffmpeg -ss 00:00:05 -i video.mp4 -vframes 1 -vf scale=320:-1 thumb.jpg

HLS Streaming

# Generate HLS playlist
ffmpeg -i input.mp4 \
  -c:v libx264 -preset fast -crf 22 -g 48 \
  -c:a aac -b:a 128k \
  -f hls -hls_time 6 -hls_playlist_type vod \
  playlist.m3u8

Image Watermark

# Add watermark to corner
magick input.jpg watermark.png -gravity southeast \
  -geometry +10+10 -composite output.jpg

Common Workflows

Optimize Video for Web

# H.264 with good compression
ffmpeg -i input.mp4 \
  -c:v libx264 -preset slow -crf 23 \
  -c:a aac -b:a 128k \
  -movflags +faststart \
  output.mp4

Create Responsive Images

# Generate multiple sizes
for size in 320 640 1024 1920; do
  magick input.jpg -resize ${size}x -quality 85 "output-${size}w.jpg"
done

Extract Video Segment

# From 1:30 to 3:00 (re-encode for precision)
ffmpeg -i input.mp4 -ss 00:01:30 -to 00:03:00 \
  -c:v libx264 -c:a aac output.mp4

Batch Image Optimization

# Convert PNG to optimized JPEG
mogrify -path ./optimized -format jpg -quality 85 -strip *.png

Video GIF Creation

# High quality GIF with palette
ffmpeg -i input.mp4 -vf "fps=15,scale=640:-1:flags=lanczos,split[s0][s1];[s0]palettegen[p];[s1][p]paletteuse" output.gif

Image Blur Effect

# Gaussian blur
magick input.jpg -gaussian-blur 0x8 output.jpg

Advanced Techniques

Multi-Pass Video Encoding

# Pass 1 (analysis)
ffmpeg -y -i input.mkv -c:v libx264 -b:v 2600k -pass 1 -an -f null /dev/null

# Pass 2 (encoding)
ffmpeg -i input.mkv -c:v libx264 -b:v 2600k -pass 2 -c:a aac output.mp4

Hardware-Accelerated Encoding

# NVIDIA NVENC
ffmpeg -hwaccel cuda -i input.mp4 -c:v h264_nvenc -preset fast -crf 22 output.mp4

# Intel QuickSync
ffmpeg -hwaccel qsv -c:v h264_qsv -i input.mp4 -c:v h264_qsv output.mp4

Complex Image Pipeline

# Resize, crop, border, adjust
magick input.jpg \
  -resize 1000x1000^ \
  -gravity center \
  -crop 1000x1000+0+0 +repage \
  -bordercolor black -border 5x5 \
  -brightness-contrast 5x10 \
  -quality 90 \
  output.jpg

Video Filter Chains

# Scale, denoise, watermark
ffmpeg -i video.mp4 -i logo.png \
  -filter_complex "[0:v]scale=1280:720,hqdn3d[v];[v][1:v]overlay=10:10" \
  -c:a copy output.mp4

Animated GIF from Images

# Create with delay
magick -delay 100 -loop 0 frame*.png animated.gif

# Optimize size
magick animated.gif -fuzz 5% -layers Optimize optimized.gif

Media Analysis

Inspect Video Properties

# Detailed JSON output
ffprobe -v quiet -print_format json -show_format -show_streams input.mp4

# Get resolution
ffprobe -v error -select_streams v:0 \
  -show_entries stream=width,height \
  -of csv=s=x:p=0 input.mp4

Image Information

# Basic info
identify image.jpg

# Detailed format
identify -verbose image.jpg

# Custom format
identify -format "%f: %wx%h %b\n" image.jpg

Performance Tips

1. Use CRF for quality control - Better than bitrate for video
2. Copy streams when possible - Avoid re-encoding with -c copy
3. Hardware acceleration - GPU encoding 5-10x faster
4. Appropriate presets - Balance speed vs compression
5. Batch with mogrify - In-place image processing
6. Strip metadata - Reduce file size with -strip
7. Progressive JPEG - Better web loading with -interlace Plane
8. Limit memory - Prevent crashes on large batches
9. Test on samples - Verify settings before batch
10. Parallel processing - Use GNU Parallel for multiple files

Reference Documentation

Detailed guides in references/:

• ffmpeg-encoding.md - Video/audio codecs, quality optimization, hardware acceleration
• ffmpeg-streaming.md - HLS/DASH, live streaming, adaptive bitrate
• ffmpeg-filters.md - Video/audio filters, complex filtergraphs
• imagemagick-editing.md - Format conversion, effects, transformations
• imagemagick-batch.md - Batch processing, mogrify, parallel operations
• format-compatibility.md - Format support, codec recommendations

Common Parameters

FFmpeg Video

• -c:v - Video codec (libx264, libx265, libvpx-vp9)
• -crf - Quality (0-51, lower=better, 23=default)
• -preset - Speed/compression (ultrafast to veryslow)
• -b:v - Video bitrate (e.g., 2M, 2500k)
• -vf - Video filters

FFmpeg Audio

• -c:a - Audio codec (aac, mp3, opus)
• -b:a - Audio bitrate (e.g., 128k, 192k)
• -ar - Sample rate (44100, 48000)

ImageMagick Geometry

• 800x600 - Fit within (maintains aspect)
• 800x600! - Force exact size
• 800x600^ - Fill (may crop)
• 800x - Width only
• x600 - Height only
• 50% - Scale percentage

Troubleshooting

FFmpeg "Unknown encoder"

# Check available encoders
ffmpeg -encoders | grep h264

# Install codec libraries
sudo apt-get install libx264-dev libx265-dev

ImageMagick "not authorized"

# Edit policy file
sudo nano /etc/ImageMagick-7/policy.xml
# Change <policy domain="coder" rights="none" pattern="PDF" />
# to <policy domain="coder" rights="read|write" pattern="PDF" />

Memory errors

# Limit memory usage
ffmpeg -threads 4 input.mp4 output.mp4
magick -limit memory 2GB -limit map 4GB input.jpg output.jpg

Resources

• FFmpeg: https://ffmpeg.org/documentation.html
• FFmpeg Wiki: https://trac.ffmpeg.org/
• ImageMagick: https://imagemagick.org/
• ImageMagick Usage: https://imagemagick.org/Usage/