benchflow-ai / ffmpeg-audio-processing

Skill Content

---
name: FFmpeg Audio Processing
description: Extract, normalize, mix, and process audio tracks - audio manipulation and analysis
---

# FFmpeg Audio Processing Skill

Extract, normalize, mix, and process audio tracks from video files.

## When to Use

- Extract audio from video
- Normalize audio levels
- Mix multiple audio tracks
- Convert audio formats
- Extract specific channels
- Adjust audio volume

## Extract Audio

```bash
# Extract as MP3
ffmpeg -i video.mp4 -vn -acodec libmp3lame -q:a 2 audio.mp3

# Extract as AAC (copy, no re-encode)
ffmpeg -i video.mp4 -vn -c:a copy audio.aac

# Extract as WAV (uncompressed)
ffmpeg -i video.mp4 -vn -acodec pcm_s16le audio.wav

# Extract specific audio stream
ffmpeg -i video.mp4 -map 0:a:1 -c:a copy audio2.aac
```

## Normalize Audio

```bash
# Normalize loudness (ITU-R BS.1770-4)
ffmpeg -i input.mp4 -af "loudnorm=I=-23:TP=-1.5:LRA=11" output.mp4

# Simple normalization
ffmpeg -i input.mp4 -af "volume=2.0" output.mp4

# Peak normalization
ffmpeg -i input.mp4 -af "volumedetect" -f null -
# Then use the detected peak to normalize
ffmpeg -i input.mp4 -af "volume=0.5" output.mp4
```

## Volume Adjustment

```bash
# Increase volume by 6dB
ffmpeg -i input.mp4 -af "volume=6dB" output.mp4

# Decrease volume by 3dB
ffmpeg -i input.mp4 -af "volume=-3dB" output.mp4

# Set absolute volume
ffmpeg -i input.mp4 -af "volume=0.5" output.mp4
```

## Channel Operations

```bash
# Extract left channel
ffmpeg -i stereo.mp3 -map_channel 0.0.0 left.mp3

# Extract right channel
ffmpeg -i stereo.mp3 -map_channel 0.0.1 right.mp3

# Convert stereo to mono
ffmpeg -i stereo.mp3 -ac 1 mono.mp3

# Convert mono to stereo
ffmpeg -i mono.mp3 -ac 2 stereo.mp3
```

## Mix Audio Tracks

```bash
# Replace audio track
ffmpeg -i video.mp4 -i audio.mp3 -c:v copy -map 0:v:0 -map 1:a:0 output.mp4

# Mix two audio tracks
ffmpeg -i video.mp4 -i audio2.mp3 \
  -filter_complex "[0:a][1:a]amix=inputs=2:duration=first" \
  -c:v copy output.mp4

# Mix with volume control
ffmpeg -i video.mp4 -i bgm.mp3 \
  -filter_complex "[0:a]volume=1.0[voice];[1:a]volume=0.3[music];[voice][music]amix=inputs=2:duration=first" \
  -c:v copy output.mp4
```

## Audio Delay

```bash
# Delay audio by 0.5 seconds
ffmpeg -i video.mp4 -itsoffset 0.5 -i video.mp4 \
  -map 0:v -map 1:a -c copy output.mp4

# Using adelay filter (milliseconds)
ffmpeg -i input.mp4 -af "adelay=500|500" output.mp4
```

## Sample Rate Conversion

```bash
# Resample to 48kHz
ffmpeg -i input.mp4 -af "aresample=48000" output.mp4

# Resample audio only
ffmpeg -i input.mp4 -vn -af "aresample=48000" -ar 48000 audio.wav
```

## Audio Filters

```bash
# High-pass filter (remove low frequencies)
ffmpeg -i input.mp4 -af "highpass=f=200" output.mp4

# Low-pass filter (remove high frequencies)
ffmpeg -i input.mp4 -af "lowpass=f=3000" output.mp4

# Band-pass filter
ffmpeg -i input.mp4 -af "bandpass=f=1000:width_type=h:w=500" output.mp4

# Fade in/out
ffmpeg -i input.mp4 -af "afade=t=in:st=0:d=2,afade=t=out:st=8:d=2" output.mp4
```

## Audio Analysis

```bash
# Detect volume levels
ffmpeg -i input.mp4 -af "volumedetect" -f null -

# Measure loudness (LUFS)
ffmpeg -i input.mp4 -af "ebur128=peak=true" -f null -

# Get audio statistics
ffprobe -v error -select_streams a:0 \
  -show_entries stream=sample_rate,channels,bit_rate \
  -of json input.mp4
```

## Combine Multiple Audio Files

```bash
# Concatenate audio files
ffmpeg -i "concat:audio1.mp3|audio2.mp3|audio3.mp3" -c copy output.mp3

# Using file list
# file 'audio1.mp3'
# file 'audio2.mp3'
ffmpeg -f concat -safe 0 -i list.txt -c copy output.mp3
```

## Notes

- Use `-vn` to disable video when extracting audio
- `-map` to select specific streams
- `-af` for audio filters
- `-ac` for channel count
- `-ar` for sample rate
- Normalization may require two passes for accurate results