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gh-rafaelcalleja-claude-mar…/skills/media-processing/references/ffmpeg-encoding.md
Zhongwei Li 6ec3196ecc Initial commit
2025-11-30 08:48:52 +08:00

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FFmpeg Video & Audio Encoding

Complete guide to codec selection, quality optimization, and hardware acceleration.

Video Codecs

H.264 (libx264)

Most widely supported codec, excellent compression/quality balance.

Best for: Universal compatibility, streaming, web video

Quality range: CRF 17-28 (lower = better)

# High quality
ffmpeg -i input.mkv -c:v libx264 -preset slow -crf 18 -c:a copy output.mp4

# Standard quality (recommended)
ffmpeg -i input.mkv -c:v libx264 -preset medium -crf 23 -c:a copy output.mp4

# Fast encoding
ffmpeg -i input.mkv -c:v libx264 -preset fast -crf 23 -c:a copy output.mp4

H.265/HEVC (libx265)

25-50% better compression than H.264, slower encoding.

Best for: 4K video, file size reduction, archival

# High quality 4K
ffmpeg -i input.mkv -c:v libx265 -preset medium -crf 24 -c:a copy output.mp4

# Balanced quality
ffmpeg -i input.mkv -c:v libx265 -preset fast -crf 26 -c:a copy output.mp4

VP9 (libvpx-vp9)

Royalty-free, WebM format, good for YouTube and open-source projects.

Best for: YouTube, Chrome/Firefox, open platforms

# Quality-based (recommended)
ffmpeg -i input.mkv -c:v libvpx-vp9 -crf 30 -b:v 0 -c:a libopus output.webm

# Two-pass for better quality
ffmpeg -i input.mkv -c:v libvpx-vp9 -b:v 2M -pass 1 -an -f null /dev/null
ffmpeg -i input.mkv -c:v libvpx-vp9 -b:v 2M -pass 2 -c:a libopus output.webm

AV1 (libaom-av1, libsvtav1)

Next-generation codec, best compression, very slow encoding.

Best for: Future-proofing, maximum compression, low bandwidth

# Using libaom (slow, highest quality)
ffmpeg -i input.mkv -c:v libaom-av1 -crf 30 -b:v 0 -strict experimental output.mp4

# Using SVT-AV1 (faster)
ffmpeg -i input.mkv -c:v libsvtav1 -crf 30 -preset 5 output.mp4

Audio Codecs

AAC (Industry Standard)

Best quality for streaming, universal support.

# High quality
ffmpeg -i input.mp4 -c:a aac -b:a 192k output.mp4

# Standard quality
ffmpeg -i input.mp4 -c:a aac -b:a 128k output.mp4

# Low bitrate
ffmpeg -i input.mp4 -c:a aac -b:a 96k output.mp4

MP3 (libmp3lame)

Universal compatibility, good quality.

# Variable bitrate (best quality)
ffmpeg -i input.wav -c:a libmp3lame -q:a 0 output.mp3

# Constant bitrate
ffmpeg -i input.wav -c:a libmp3lame -b:a 192k output.mp3

Opus (libopus)

Best quality at low bitrates, ideal for voice and streaming.

# Voice (mono)
ffmpeg -i input.mp4 -c:a libopus -b:a 32k -ac 1 output.webm

# Music (stereo)
ffmpeg -i input.mp4 -c:a libopus -b:a 128k output.webm

FLAC (Lossless)

No quality loss, archival quality, larger files.

# Lossless audio
ffmpeg -i input.wav -c:a flac output.flac

# Extract audio losslessly
ffmpeg -i video.mp4 -c:a flac audio.flac

Quality Optimization

CRF (Constant Rate Factor)

Best for quality-focused encoding. Single-pass, adjusts bitrate for complexity.

CRF Scale:

  • 0 = Lossless (huge files)
  • 17-18 = Visually lossless
  • 20-23 = High quality (recommended)
  • 24-28 = Medium quality
  • 30+ = Low quality
  • 51 = Worst quality
# Visually lossless
ffmpeg -i input.mp4 -c:v libx264 -crf 18 -preset slow output.mp4

# High quality (recommended)
ffmpeg -i input.mp4 -c:v libx264 -crf 22 -preset medium output.mp4

# Balanced quality/size
ffmpeg -i input.mp4 -c:v libx264 -crf 25 -preset fast output.mp4

Bitrate-Based Encoding

Target specific file size or quality. Two-pass recommended.

# Calculate target bitrate
# bitrate = (target_size_MB * 8192) / duration_seconds - audio_bitrate

# Two-pass encoding (2600k video, 128k audio)
ffmpeg -y -i input.mkv -c:v libx264 -b:v 2600k -pass 1 -an -f null /dev/null
ffmpeg -i input.mkv -c:v libx264 -b:v 2600k -pass 2 -c:a aac -b:a 128k output.mp4

Presets (Speed vs Compression)

Trade-off between encoding speed and file size.

Available presets:

  • ultrafast - Fastest, largest files
  • superfast
  • veryfast
  • faster
  • fast
  • medium - Default balance
  • slow - Better compression
  • slower
  • veryslow - Best compression
  • placebo - Not recommended (minimal gains)
# Fast encoding (real-time)
ffmpeg -i input.mp4 -c:v libx264 -preset ultrafast -crf 23 output.mp4

# Balanced
ffmpeg -i input.mp4 -c:v libx264 -preset medium -crf 22 output.mp4

# Best compression (slow)
ffmpeg -i input.mp4 -c:v libx264 -preset veryslow -crf 20 output.mp4

Hardware Acceleration

NVIDIA NVENC

5-10x faster encoding, slightly larger files than software encoding.

Requirements: NVIDIA GPU (GTX 10xx or newer)

# H.264 with NVENC
ffmpeg -hwaccel cuda -i input.mp4 -c:v h264_nvenc -preset fast -crf 22 output.mp4

# H.265 with NVENC
ffmpeg -hwaccel cuda -i input.mp4 -c:v hevc_nvenc -preset slow -crf 24 output.mp4

# Quality levels (instead of CRF)
ffmpeg -hwaccel cuda -i input.mp4 -c:v h264_nvenc -preset slow -rc vbr -cq 22 output.mp4

NVENC Presets:

  • default - Balanced
  • slow - Better quality
  • medium
  • fast
  • hp - High performance
  • hq - High quality
  • bd - Bluray disk
  • ll - Low latency
  • llhq - Low latency high quality
  • llhp - Low latency high performance

Intel QuickSync (QSV)

Fast hardware encoding on Intel CPUs with integrated graphics.

Requirements: Intel CPU with Quick Sync Video support

# H.264 with QSV
ffmpeg -hwaccel qsv -c:v h264_qsv -i input.mp4 \
  -c:v h264_qsv -preset fast -global_quality 22 output.mp4

# H.265 with QSV
ffmpeg -hwaccel qsv -c:v hevc_qsv -i input.mp4 \
  -c:v hevc_qsv -preset medium -global_quality 24 output.mp4

# Quality levels
ffmpeg -hwaccel qsv -i input.mp4 -c:v h264_qsv -global_quality 20 output.mp4

AMD VCE/VCN

Hardware encoding on AMD GPUs.

Requirements: AMD GPU with VCE/VCN support

# H.264 with AMF
ffmpeg -hwaccel auto -i input.mp4 \
  -c:v h264_amf -quality balanced -rc cqp -qp 22 output.mp4

# H.265 with AMF
ffmpeg -hwaccel auto -i input.mp4 \
  -c:v hevc_amf -quality quality -rc cqp -qp 24 output.mp4

Apple VideoToolbox (macOS)

Hardware encoding on macOS devices.

# H.264 with VideoToolbox
ffmpeg -i input.mp4 -c:v h264_videotoolbox -b:v 2M output.mp4

# H.265 with VideoToolbox
ffmpeg -i input.mp4 -c:v hevc_videotoolbox -b:v 1.5M output.mp4

Performance Tuning

Multi-Threading

FFmpeg automatically uses multiple cores. Override if needed:

# Limit threads
ffmpeg -threads 4 -i input.mp4 -c:v libx264 output.mp4

# Auto (default)
ffmpeg -threads 0 -i input.mp4 -c:v libx264 output.mp4

Tune Options

Optimize encoder for specific content types:

# Film content
ffmpeg -i input.mp4 -c:v libx264 -tune film -crf 22 output.mp4

# Animation
ffmpeg -i input.mp4 -c:v libx264 -tune animation -crf 22 output.mp4

# Grain (film with noise)
ffmpeg -i input.mp4 -c:v libx264 -tune grain -crf 22 output.mp4

# Low latency streaming
ffmpeg -i input.mp4 -c:v libx264 -tune zerolatency -crf 22 output.mp4

# Screen content (sharp edges)
ffmpeg -i input.mp4 -c:v libx264 -tune stillimage -crf 22 output.mp4

Codec Selection Guide

Use Cases

Use Case Codec Settings
Web video H.264 CRF 23, preset medium
4K streaming H.265 CRF 24, preset fast
YouTube upload VP9 or H.264 CRF 23
Archive H.265 or H.264 CRF 18, preset slow
Low bandwidth AV1 or H.265 CRF 30
Fast encoding H.264 NVENC preset fast
Maximum compatibility H.264 profile main, level 4.0

Platform Compatibility

Platform Recommended Supported
Web browsers H.264 H.264, VP9, AV1
Mobile devices H.264 H.264, H.265
Smart TVs H.264 H.264, H.265
YouTube VP9, H.264 All
Social media H.264 H.264

Best Practices

  1. Use CRF for most tasks - Better than bitrate for variable content
  2. Start with CRF 23 - Good balance, adjust based on results
  3. Use slow preset - For archival and final delivery
  4. Use fast preset - For previews and testing
  5. Hardware acceleration - When speed is critical
  6. Two-pass encoding - When file size is fixed
  7. Match source frame rate - Don't increase FPS
  8. Don't upscale resolution - Keep original or downscale
  9. Test on short clips - Verify settings before full encode
  10. Keep source files - Original quality for re-encoding

Troubleshooting

Poor Quality Output

# Lower CRF value
ffmpeg -i input.mp4 -c:v libx264 -crf 18 -preset slow output.mp4

# Use slower preset
ffmpeg -i input.mp4 -c:v libx264 -crf 22 -preset veryslow output.mp4

# Increase bitrate (two-pass)
ffmpeg -y -i input.mp4 -c:v libx264 -b:v 5M -pass 1 -an -f null /dev/null
ffmpeg -i input.mp4 -c:v libx264 -b:v 5M -pass 2 -c:a aac output.mp4

Slow Encoding

# Use faster preset
ffmpeg -i input.mp4 -c:v libx264 -preset ultrafast output.mp4

# Use hardware acceleration
ffmpeg -hwaccel cuda -i input.mp4 -c:v h264_nvenc output.mp4

# Reduce resolution
ffmpeg -i input.mp4 -vf scale=1280:-1 -c:v libx264 output.mp4

Large File Size

# Increase CRF
ffmpeg -i input.mp4 -c:v libx264 -crf 26 output.mp4

# Use better codec
ffmpeg -i input.mp4 -c:v libx265 -crf 26 output.mp4

# Two-pass with target bitrate
ffmpeg -y -i input.mp4 -c:v libx264 -b:v 1M -pass 1 -an -f null /dev/null
ffmpeg -i input.mp4 -c:v libx264 -b:v 1M -pass 2 -c:a aac output.mp4
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