# 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)

```bash
# 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

```bash
# 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

```bash
# 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

```bash
# 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.

```bash
# 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.

```bash
# 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.

```bash
# 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.

```bash
# 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

```bash
# 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.

```bash
# 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)

```bash
# 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)

```bash
# 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

```bash
# 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

```bash
# 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.

```bash
# 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:

```bash
# 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:

```bash
# 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

```bash
# 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

```bash
# 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

```bash
# 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
```