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Zhongwei Li
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skills/media-processing/references/ffmpeg-encoding.md
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skills/media-processing/references/ffmpeg-encoding.md
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# FFmpeg Video & Audio Encoding
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Complete guide to codec selection, quality optimization, and hardware acceleration.
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## Video Codecs
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### H.264 (libx264)
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Most widely supported codec, excellent compression/quality balance.
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**Best for:** Universal compatibility, streaming, web video
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**Quality range:** CRF 17-28 (lower = better)
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```bash
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# High quality
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ffmpeg -i input.mkv -c:v libx264 -preset slow -crf 18 -c:a copy output.mp4
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# Standard quality (recommended)
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ffmpeg -i input.mkv -c:v libx264 -preset medium -crf 23 -c:a copy output.mp4
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# Fast encoding
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ffmpeg -i input.mkv -c:v libx264 -preset fast -crf 23 -c:a copy output.mp4
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```
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### H.265/HEVC (libx265)
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25-50% better compression than H.264, slower encoding.
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**Best for:** 4K video, file size reduction, archival
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```bash
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# High quality 4K
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ffmpeg -i input.mkv -c:v libx265 -preset medium -crf 24 -c:a copy output.mp4
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# Balanced quality
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ffmpeg -i input.mkv -c:v libx265 -preset fast -crf 26 -c:a copy output.mp4
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```
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### VP9 (libvpx-vp9)
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Royalty-free, WebM format, good for YouTube and open-source projects.
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**Best for:** YouTube, Chrome/Firefox, open platforms
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```bash
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# Quality-based (recommended)
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ffmpeg -i input.mkv -c:v libvpx-vp9 -crf 30 -b:v 0 -c:a libopus output.webm
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# Two-pass for better quality
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ffmpeg -i input.mkv -c:v libvpx-vp9 -b:v 2M -pass 1 -an -f null /dev/null
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ffmpeg -i input.mkv -c:v libvpx-vp9 -b:v 2M -pass 2 -c:a libopus output.webm
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```
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### AV1 (libaom-av1, libsvtav1)
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Next-generation codec, best compression, very slow encoding.
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**Best for:** Future-proofing, maximum compression, low bandwidth
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```bash
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# Using libaom (slow, highest quality)
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ffmpeg -i input.mkv -c:v libaom-av1 -crf 30 -b:v 0 -strict experimental output.mp4
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# Using SVT-AV1 (faster)
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ffmpeg -i input.mkv -c:v libsvtav1 -crf 30 -preset 5 output.mp4
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```
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## Audio Codecs
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### AAC (Industry Standard)
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Best quality for streaming, universal support.
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```bash
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# High quality
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ffmpeg -i input.mp4 -c:a aac -b:a 192k output.mp4
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# Standard quality
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ffmpeg -i input.mp4 -c:a aac -b:a 128k output.mp4
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# Low bitrate
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ffmpeg -i input.mp4 -c:a aac -b:a 96k output.mp4
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```
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### MP3 (libmp3lame)
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Universal compatibility, good quality.
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```bash
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# Variable bitrate (best quality)
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ffmpeg -i input.wav -c:a libmp3lame -q:a 0 output.mp3
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# Constant bitrate
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ffmpeg -i input.wav -c:a libmp3lame -b:a 192k output.mp3
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```
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### Opus (libopus)
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Best quality at low bitrates, ideal for voice and streaming.
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```bash
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# Voice (mono)
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ffmpeg -i input.mp4 -c:a libopus -b:a 32k -ac 1 output.webm
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# Music (stereo)
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ffmpeg -i input.mp4 -c:a libopus -b:a 128k output.webm
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```
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### FLAC (Lossless)
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No quality loss, archival quality, larger files.
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```bash
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# Lossless audio
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ffmpeg -i input.wav -c:a flac output.flac
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# Extract audio losslessly
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ffmpeg -i video.mp4 -c:a flac audio.flac
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```
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## Quality Optimization
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### CRF (Constant Rate Factor)
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Best for quality-focused encoding. Single-pass, adjusts bitrate for complexity.
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**CRF Scale:**
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- 0 = Lossless (huge files)
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- 17-18 = Visually lossless
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- 20-23 = High quality (recommended)
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- 24-28 = Medium quality
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- 30+ = Low quality
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- 51 = Worst quality
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```bash
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# Visually lossless
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ffmpeg -i input.mp4 -c:v libx264 -crf 18 -preset slow output.mp4
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# High quality (recommended)
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ffmpeg -i input.mp4 -c:v libx264 -crf 22 -preset medium output.mp4
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# Balanced quality/size
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ffmpeg -i input.mp4 -c:v libx264 -crf 25 -preset fast output.mp4
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```
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### Bitrate-Based Encoding
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Target specific file size or quality. Two-pass recommended.
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```bash
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# Calculate target bitrate
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# bitrate = (target_size_MB * 8192) / duration_seconds - audio_bitrate
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# Two-pass encoding (2600k video, 128k audio)
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ffmpeg -y -i input.mkv -c:v libx264 -b:v 2600k -pass 1 -an -f null /dev/null
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ffmpeg -i input.mkv -c:v libx264 -b:v 2600k -pass 2 -c:a aac -b:a 128k output.mp4
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```
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### Presets (Speed vs Compression)
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Trade-off between encoding speed and file size.
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**Available presets:**
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- `ultrafast` - Fastest, largest files
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- `superfast`
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- `veryfast`
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- `faster`
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- `fast`
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- `medium` - Default balance
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- `slow` - Better compression
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- `slower`
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- `veryslow` - Best compression
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- `placebo` - Not recommended (minimal gains)
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```bash
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# Fast encoding (real-time)
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ffmpeg -i input.mp4 -c:v libx264 -preset ultrafast -crf 23 output.mp4
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# Balanced
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ffmpeg -i input.mp4 -c:v libx264 -preset medium -crf 22 output.mp4
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# Best compression (slow)
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ffmpeg -i input.mp4 -c:v libx264 -preset veryslow -crf 20 output.mp4
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```
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## Hardware Acceleration
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### NVIDIA NVENC
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5-10x faster encoding, slightly larger files than software encoding.
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**Requirements:** NVIDIA GPU (GTX 10xx or newer)
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```bash
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# H.264 with NVENC
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ffmpeg -hwaccel cuda -i input.mp4 -c:v h264_nvenc -preset fast -crf 22 output.mp4
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# H.265 with NVENC
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ffmpeg -hwaccel cuda -i input.mp4 -c:v hevc_nvenc -preset slow -crf 24 output.mp4
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# Quality levels (instead of CRF)
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ffmpeg -hwaccel cuda -i input.mp4 -c:v h264_nvenc -preset slow -rc vbr -cq 22 output.mp4
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```
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**NVENC Presets:**
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- `default` - Balanced
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- `slow` - Better quality
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- `medium`
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- `fast`
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- `hp` - High performance
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- `hq` - High quality
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- `bd` - Bluray disk
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- `ll` - Low latency
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- `llhq` - Low latency high quality
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- `llhp` - Low latency high performance
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### Intel QuickSync (QSV)
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Fast hardware encoding on Intel CPUs with integrated graphics.
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**Requirements:** Intel CPU with Quick Sync Video support
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```bash
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# H.264 with QSV
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ffmpeg -hwaccel qsv -c:v h264_qsv -i input.mp4 \
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-c:v h264_qsv -preset fast -global_quality 22 output.mp4
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# H.265 with QSV
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ffmpeg -hwaccel qsv -c:v hevc_qsv -i input.mp4 \
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-c:v hevc_qsv -preset medium -global_quality 24 output.mp4
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# Quality levels
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ffmpeg -hwaccel qsv -i input.mp4 -c:v h264_qsv -global_quality 20 output.mp4
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```
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### AMD VCE/VCN
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Hardware encoding on AMD GPUs.
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**Requirements:** AMD GPU with VCE/VCN support
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```bash
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# H.264 with AMF
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ffmpeg -hwaccel auto -i input.mp4 \
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-c:v h264_amf -quality balanced -rc cqp -qp 22 output.mp4
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# H.265 with AMF
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ffmpeg -hwaccel auto -i input.mp4 \
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-c:v hevc_amf -quality quality -rc cqp -qp 24 output.mp4
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```
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### Apple VideoToolbox (macOS)
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Hardware encoding on macOS devices.
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```bash
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# H.264 with VideoToolbox
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ffmpeg -i input.mp4 -c:v h264_videotoolbox -b:v 2M output.mp4
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# H.265 with VideoToolbox
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ffmpeg -i input.mp4 -c:v hevc_videotoolbox -b:v 1.5M output.mp4
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```
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## Performance Tuning
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### Multi-Threading
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FFmpeg automatically uses multiple cores. Override if needed:
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```bash
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# Limit threads
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ffmpeg -threads 4 -i input.mp4 -c:v libx264 output.mp4
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# Auto (default)
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ffmpeg -threads 0 -i input.mp4 -c:v libx264 output.mp4
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```
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### Tune Options
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Optimize encoder for specific content types:
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```bash
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# Film content
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ffmpeg -i input.mp4 -c:v libx264 -tune film -crf 22 output.mp4
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# Animation
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ffmpeg -i input.mp4 -c:v libx264 -tune animation -crf 22 output.mp4
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# Grain (film with noise)
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ffmpeg -i input.mp4 -c:v libx264 -tune grain -crf 22 output.mp4
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# Low latency streaming
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ffmpeg -i input.mp4 -c:v libx264 -tune zerolatency -crf 22 output.mp4
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# Screen content (sharp edges)
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ffmpeg -i input.mp4 -c:v libx264 -tune stillimage -crf 22 output.mp4
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```
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## Codec Selection Guide
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### Use Cases
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| Use Case | Codec | Settings |
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|----------|-------|----------|
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| Web video | H.264 | CRF 23, preset medium |
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| 4K streaming | H.265 | CRF 24, preset fast |
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| YouTube upload | VP9 or H.264 | CRF 23 |
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| Archive | H.265 or H.264 | CRF 18, preset slow |
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| Low bandwidth | AV1 or H.265 | CRF 30 |
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| Fast encoding | H.264 NVENC | preset fast |
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| Maximum compatibility | H.264 | profile main, level 4.0 |
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### Platform Compatibility
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| Platform | Recommended | Supported |
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|----------|------------|-----------|
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| Web browsers | H.264 | H.264, VP9, AV1 |
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| Mobile devices | H.264 | H.264, H.265 |
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| Smart TVs | H.264 | H.264, H.265 |
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| YouTube | VP9, H.264 | All |
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| Social media | H.264 | H.264 |
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## Best Practices
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1. **Use CRF for most tasks** - Better than bitrate for variable content
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2. **Start with CRF 23** - Good balance, adjust based on results
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3. **Use slow preset** - For archival and final delivery
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4. **Use fast preset** - For previews and testing
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5. **Hardware acceleration** - When speed is critical
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6. **Two-pass encoding** - When file size is fixed
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7. **Match source frame rate** - Don't increase FPS
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8. **Don't upscale resolution** - Keep original or downscale
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9. **Test on short clips** - Verify settings before full encode
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10. **Keep source files** - Original quality for re-encoding
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## Troubleshooting
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### Poor Quality Output
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```bash
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# Lower CRF value
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ffmpeg -i input.mp4 -c:v libx264 -crf 18 -preset slow output.mp4
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# Use slower preset
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ffmpeg -i input.mp4 -c:v libx264 -crf 22 -preset veryslow output.mp4
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# Increase bitrate (two-pass)
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ffmpeg -y -i input.mp4 -c:v libx264 -b:v 5M -pass 1 -an -f null /dev/null
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ffmpeg -i input.mp4 -c:v libx264 -b:v 5M -pass 2 -c:a aac output.mp4
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```
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### Slow Encoding
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```bash
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# Use faster preset
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ffmpeg -i input.mp4 -c:v libx264 -preset ultrafast output.mp4
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# Use hardware acceleration
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ffmpeg -hwaccel cuda -i input.mp4 -c:v h264_nvenc output.mp4
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# Reduce resolution
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ffmpeg -i input.mp4 -vf scale=1280:-1 -c:v libx264 output.mp4
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```
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### Large File Size
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```bash
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# Increase CRF
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ffmpeg -i input.mp4 -c:v libx264 -crf 26 output.mp4
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# Use better codec
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ffmpeg -i input.mp4 -c:v libx265 -crf 26 output.mp4
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# Two-pass with target bitrate
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ffmpeg -y -i input.mp4 -c:v libx264 -b:v 1M -pass 1 -an -f null /dev/null
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ffmpeg -i input.mp4 -c:v libx264 -b:v 1M -pass 2 -c:a aac output.mp4
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```
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