FFmpeg Format Conversion Skill

Convert media files between different formats and containers.

When to Use

• Convert video containers (MP4, MKV, AVI, etc.)
• Convert audio formats (MP3, AAC, WAV, etc.)
• Transcode to different codecs
• Copy streams without re-encoding (fast)

Basic Conversion

# Convert container format (re-encode)
ffmpeg -i input.avi output.mp4

# Copy streams without re-encoding (fast, no quality loss)
ffmpeg -i input.mp4 -c copy output.mkv

# Convert with specific codec
ffmpeg -i input.mp4 -c:v libx264 -c:a aac output.mp4

Video Codec Conversion

# H.264
ffmpeg -i input.mp4 -c:v libx264 output.mp4

# H.265 (better compression)
ffmpeg -i input.mp4 -c:v libx265 output.mp4

# VP9 (web optimized)
ffmpeg -i input.mp4 -c:v libvpx-vp9 output.webm

# AV1 (modern codec)
ffmpeg -i input.mp4 -c:v libaom-av1 output.mp4

Audio Format Conversion

# MP3
ffmpeg -i input.wav -acodec libmp3lame -q:a 2 output.mp3

# AAC
ffmpeg -i input.wav -c:a aac -b:a 192k output.m4a

# Opus (best quality/bitrate)
ffmpeg -i input.wav -c:a libopus -b:a 128k output.opus

# FLAC (lossless)
ffmpeg -i input.wav -c:a flac output.flac

Quality Settings

# CRF (Constant Rate Factor) - lower is better quality
ffmpeg -i input.mp4 -c:v libx264 -crf 23 output.mp4

# Bitrate
ffmpeg -i input.mp4 -b:v 2M -b:a 192k output.mp4

# Two-pass encoding (best quality)
ffmpeg -i input.mp4 -c:v libx264 -b:v 2M -pass 1 -f null /dev/null
ffmpeg -i input.mp4 -c:v libx264 -b:v 2M -pass 2 output.mp4

Presets

# Encoding speed presets (faster = larger file)
ffmpeg -i input.mp4 -c:v libx264 -preset fast output.mp4
# Options: ultrafast, superfast, veryfast, faster, fast, medium, slow, slower, veryslow

# Quality presets
ffmpeg -i input.mp4 -c:v libx264 -preset slow -crf 18 output.mp4

Batch Conversion

# Convert all MKV to MP4
for f in *.mkv; do
  ffmpeg -i "$f" -c copy "${f%.mkv}.mp4"
done

# Convert with re-encoding
for f in *.avi; do
  ffmpeg -i "$f" -c:v libx264 -c:a aac "${f%.avi}.mp4"
done

Common Codecs

Video

• H.264 (libx264) - Universal compatibility
• H.265 (libx265) - Better compression
• VP9 (libvpx-vp9) - Open standard
• AV1 (libaom-av1) - Modern codec

Audio

• AAC (aac) - Universal
• MP3 (libmp3lame) - Legacy
• Opus (libopus) - Best quality/bitrate
• FLAC (flac) - Lossless

Notes

• Use -c copy when possible for speed (no re-encoding)
• Re-encoding is slower but allows codec/quality changes
• CRF 18-23 is good quality range for H.264
• Preset affects encoding speed vs file size tradeoff