CRITICAL GUIDELINES

Windows File Path Requirements

MANDATORY: Always Use Backslashes on Windows for File Paths

When using Edit or Write tools on Windows, you MUST use backslashes (\) in file paths, NOT forward slashes (/).

Quick Reference

When to Use This Skill

Use for audio-focused operations:

• Extracting audio from video files
• Loudness normalization for broadcast/streaming compliance
• Podcast and audiobook processing
• Audio format conversion
• Audio effects (EQ, compression, noise reduction)

FFmpeg Audio Processing (2025)

Complete guide to audio encoding, normalization, and professional audio workflows with FFmpeg.

Audio Codec Reference

Codec Comparison

Recommended Bitrates

Basic Audio Operations

Extract Audio

# Extract to original format (no re-encode)
ffmpeg -i video.mp4 -vn -c:a copy audio.m4a

# Extract to MP3
ffmpeg -i video.mp4 -vn -c:a libmp3lame -b:a 320k audio.mp3

# Extract to AAC
ffmpeg -i video.mp4 -vn -c:a aac -b:a 256k audio.m4a

# Extract to FLAC (lossless)
ffmpeg -i video.mp4 -vn -c:a flac audio.flac

# Extract to WAV (uncompressed)
ffmpeg -i video.mp4 -vn -c:a pcm_s16le audio.wav

Convert Audio Formats

# MP3 to AAC
ffmpeg -i input.mp3 -c:a aac -b:a 256k output.m4a

# WAV to MP3
ffmpeg -i input.wav -c:a libmp3lame -b:a 320k output.mp3

# FLAC to MP3
ffmpeg -i input.flac -c:a libmp3lame -b:a 320k output.mp3

# Multiple files (batch)
for f in *.flac; do
  ffmpeg -i "$f" -c:a libmp3lame -b:a 320k "${f%.flac}.mp3"
done

Quality Settings

# AAC VBR quality (1-5, higher = better)
ffmpeg -i input.wav -c:a aac -q:a 2 output.m4a

# MP3 VBR quality (0-9, lower = better)
ffmpeg -i input.wav -c:a libmp3lame -q:a 0 output.mp3

# Opus with target bitrate
ffmpeg -i input.wav -c:a libopus -b:a 128k output.opus

Audio Normalization

Loudness Standards

EBU R128 Normalization (loudnorm)

Single-Pass (Live/Real-time)

# Quick normalization (less accurate)
ffmpeg -i input.mp3 \
  -af loudnorm=I=-16:TP=-1.5:LRA=11 \
  output.mp3

Two-Pass (Recommended)

# Pass 1: Analyze
ffmpeg -i input.mp3 \
  -af loudnorm=I=-16:TP=-1.5:LRA=11:print_format=json \
  -f null -

# Output will include:
# "input_i": "-25.23"
# "input_tp": "-0.50"
# "input_lra": "8.32"
# "input_thresh": "-35.87"
# "target_offset": "1.23"

# Pass 2: Normalize with measured values
ffmpeg -i input.mp3 \
  -af loudnorm=I=-16:TP=-1.5:LRA=11:measured_I=-25.23:measured_TP=-0.50:measured_LRA=8.32:measured_thresh=-35.87:offset=1.23:linear=true \
  -ar 48000 \
  output.mp3

Two-Pass Script

#!/bin/bash
# loudnorm-2pass.sh

INPUT="$1"
OUTPUT="$2"
TARGET_I="${3:--16}"
TARGET_TP="${4:--1.5}"
TARGET_LRA="${5:-11}"

# Pass 1: Analyze
stats=$(ffmpeg -i "$INPUT" \
  -af loudnorm=I=${TARGET_I}:TP=${TARGET_TP}:LRA=${TARGET_LRA}:print_format=json \
  -f null - 2>&1 | grep -A 12 "Parsed_loudnorm")

# Extract values
input_i=$(echo "$stats" | grep input_i | tr -d '", ' | cut -d':' -f2)
input_tp=$(echo "$stats" | grep input_tp | tr -d '", ' | cut -d':' -f2)
input_lra=$(echo "$stats" | grep input_lra | tr -d '", ' | cut -d':' -f2)
input_thresh=$(echo "$stats" | grep input_thresh | tr -d '", ' | cut -d':' -f2)
offset=$(echo "$stats" | grep target_offset | tr -d '", ' | cut -d':' -f2)

# Pass 2: Normalize
ffmpeg -i "$INPUT" \
  -af "loudnorm=I=${TARGET_I}:TP=${TARGET_TP}:LRA=${TARGET_LRA}:measured_I=${input_i}:measured_TP=${input_tp}:measured_LRA=${input_lra}:measured_thresh=${input_thresh}:offset=${offset}:linear=true" \
  -ar 48000 \
  "$OUTPUT"

Peak Normalization

# Normalize to peak level
ffmpeg -i input.mp3 \
  -af "volume=0dB:eval=once:precision=fixed" \
  -af "loudnorm=I=-16:TP=-1:LRA=11" \
  output.mp3

# Simple peak normalization
ffmpeg -i input.mp3 \
  -filter:a "volume=replaygain=peak" \
  output.mp3

RMS Normalization

# Normalize to specific RMS level
ffmpeg -i input.mp3 \
  -af "loudnorm=I=-23:LRA=7:TP=-2" \
  output.mp3

ffmpeg-normalize Tool

The ffmpeg-normalize Python utility provides an easier interface:

# Install
pip install ffmpeg-normalize

# Basic usage
ffmpeg-normalize input.mp3 -o output.mp3

# Custom target
ffmpeg-normalize input.mp3 -o output.mp3 -t -14

# Batch normalize (album mode - preserves relative loudness)
ffmpeg-normalize *.mp3 --batch -o normalized/

# Use built-in presets (v1.36.0+)
ffmpeg-normalize input.mp3 --preset podcast -o output.mp3
ffmpeg-normalize *.mp3 --preset music --batch -o normalized/

Audio Filters

Volume Control

# Increase volume by 50%
ffmpeg -i input.mp3 -af "volume=1.5" output.mp3

# Increase by 6dB
ffmpeg -i input.mp3 -af "volume=6dB" output.mp3

# Decrease by 3dB
ffmpeg -i input.mp3 -af "volume=-3dB" output.mp3

Fade In/Out

# Fade in 3 seconds, fade out last 3 seconds
ffmpeg -i input.mp3 \
  -af "afade=t=in:ss=0:d=3,afade=t=out:st=57:d=3" \
  output.mp3

# Calculate fade out start automatically
duration=$(ffprobe -v error -show_entries format=duration -of default=noprint_wrappers=1:nokey=1 input.mp3)
fadeout_start=$(echo "$duration - 3" | bc)
ffmpeg -i input.mp3 \
  -af "afade=t=in:ss=0:d=3,afade=t=out:st=${fadeout_start}:d=3" \
  output.mp3

Equalization

# Bass boost
ffmpeg -i input.mp3 \
  -af "equalizer=f=100:width_type=o:width=2:g=5" \
  output.mp3

# Treble reduction
ffmpeg -i input.mp3 \
  -af "equalizer=f=8000:width_type=o:width=2:g=-3" \
  output.mp3

# Multi-band EQ
ffmpeg -i input.mp3 \
  -af "equalizer=f=100:width_type=o:width=2:g=3,equalizer=f=1000:width_type=o:width=2:g=-2,equalizer=f=8000:width_type=o:width=2:g=2" \
  output.mp3

High-Pass / Low-Pass Filters

# High-pass filter (remove below 80Hz)
ffmpeg -i input.mp3 -af "highpass=f=80" output.mp3

# Low-pass filter (remove above 8kHz)
ffmpeg -i input.mp3 -af "lowpass=f=8000" output.mp3

# Band-pass filter
ffmpeg -i input.mp3 -af "highpass=f=80,lowpass=f=12000" output.mp3

Noise Reduction

# FFT-based noise reduction
ffmpeg -i input.mp3 \
  -af "afftdn=nf=-25" \
  output.mp3

# With noise floor adjustment
ffmpeg -i input.mp3 \
  -af "afftdn=nf=-20:tn=1" \
  output.mp3

Compressor / Limiter

# Dynamic range compression
ffmpeg -i input.mp3 \
  -af "acompressor=threshold=-20dB:ratio=4:attack=5:release=50" \
  output.mp3

# Limiter
ffmpeg -i input.mp3 \
  -af "alimiter=limit=0.9:attack=5:release=50" \
  output.mp3

# De-esser
ffmpeg -i input.mp3 \
  -af "deesser=i=0.4:f=4000:w=0.5" \
  output.mp3

Silence Detection/Removal

# Detect silence
ffmpeg -i input.mp3 \
  -af silencedetect=noise=-30dB:d=0.5 \
  -f null -

# Remove silence
ffmpeg -i input.mp3 \
  -af "silenceremove=start_periods=1:start_silence=0.5:start_threshold=-50dB:stop_periods=1:stop_silence=0.5:stop_threshold=-50dB" \
  output.mp3

Channel Operations

Stereo to Mono

# Average both channels
ffmpeg -i stereo.mp3 \
  -af "pan=mono|c0=0.5*c0+0.5*c1" \
  mono.mp3

# Use only left channel
ffmpeg -i stereo.mp3 -af "pan=mono|c0=c0" mono.mp3

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

Mono to Stereo

# Duplicate mono to both channels
ffmpeg -i mono.mp3 -af "pan=stereo|c0=c0|c1=c0" stereo.mp3

# Simple conversion
ffmpeg -i mono.mp3 -ac 2 stereo.mp3

Extract Specific Channels

# Extract left channel
ffmpeg -i stereo.mp3 \
  -filter_complex "[0:a]channelsplit=channel_layout=stereo:channels=FL[left]" \
  -map "[left]" left.mp3

# Extract right channel
ffmpeg -i stereo.mp3 \
  -filter_complex "[0:a]channelsplit=channel_layout=stereo:channels=FR[right]" \
  -map "[right]" right.mp3

5.1 Surround Operations

# Downmix 5.1 to stereo
ffmpeg -i surround.ac3 \
  -af "pan=stereo|FL=0.5*FC+0.707*FL+0.707*BL+0.5*LFE|FR=0.5*FC+0.707*FR+0.707*BR+0.5*LFE" \
  stereo.mp3

# Extract center channel
ffmpeg -i surround.ac3 \
  -filter_complex "[0:a]channelsplit=channel_layout=5.1:channels=FC[center]" \
  -map "[center]" center.mp3

Sample Rate & Bit Depth

Sample Rate Conversion

# Convert to 44.1kHz
ffmpeg -i input.wav -ar 44100 output.wav

# Convert to 48kHz
ffmpeg -i input.wav -ar 48000 output.wav

# High-quality resampling
ffmpeg -i input.wav \
  -af "aresample=resampler=soxr:precision=33:cheby=1" \
  -ar 44100 output.wav

Bit Depth Conversion

# Convert to 16-bit
ffmpeg -i input.wav -c:a pcm_s16le output.wav

# Convert to 24-bit
ffmpeg -i input.wav -c:a pcm_s24le output.wav

# Convert to 32-bit float
ffmpeg -i input.wav -c:a pcm_f32le output.wav

Speed & Pitch

Speed Change (Affects Pitch)

# 2x speed (chipmunk effect)
ffmpeg -i input.mp3 -af "atempo=2.0" output.mp3

# 0.5x speed (slow motion)
ffmpeg -i input.mp3 -af "atempo=0.5" output.mp3

# For >2x, chain filters
ffmpeg -i input.mp3 -af "atempo=2.0,atempo=2.0" output.mp3  # 4x

Pitch Change (Preserves Speed)

# Pitch shift using rubberband
ffmpeg -i input.mp3 \
  -af "rubberband=pitch=1.5" \
  output.mp3

# Pitch shift semitones
ffmpeg -i input.mp3 \
  -af "asetrate=44100*2^(2/12),aresample=44100" \
  output.mp3  # +2 semitones

Trimming & Concatenation

Trim Audio

# Extract 30 seconds starting at 1 minute
ffmpeg -ss 00:01:00 -i input.mp3 -t 00:00:30 -c copy output.mp3

# Extract from 1:00 to 2:30
ffmpeg -ss 00:01:00 -to 00:02:30 -i input.mp3 -c copy output.mp3

Concatenate Audio

# Create file list
echo "file 'part1.mp3'" > list.txt
echo "file 'part2.mp3'" >> list.txt

# Concatenate (same format)
ffmpeg -f concat -safe 0 -i list.txt -c copy output.mp3

# Concatenate with re-encode
ffmpeg -f concat -safe 0 -i list.txt -c:a aac -b:a 256k output.m4a

Crossfade

# Crossfade two files (3 second overlap)
ffmpeg -i part1.mp3 -i part2.mp3 \
  -filter_complex "acrossfade=d=3:c1=tri:c2=tri" \
  output.mp3

Professional Workflows & Troubleshooting

For complete processing chains (podcast, music mastering, broadcast EBU R128) and fixes for common post-processing issues (loudnorm resample artifact, A/V sync, re-encoding quality loss), see references/workflows-and-troubleshooting.md.

Audio Analysis & Measurement

For detailed audio analysis and measurement filters, see references/audio-analysis-measurement.md. Covers:

• astats — RMS, peak, crest factor, DC offset, bit depth, dynamic range
• ebur128 — EBU R128 / ITU-R BS.1770 integrated loudness, LRA, true-peak, with optional video meter output
• speechnorm — adaptive normalizer tuned for speech / podcasts
• dialoguenhance (FFmpeg 8.0+) — voice-band boost for poor recordings
• sofalizer — HRTF / binaural processing from SOFA files
• volumedetect — mean and peak volume detection
• aweighting — A-weighting curve for perceived loudness
• chromaprint — audio fingerprinting (raw and base64)
• Complete analysis workflow — audio-analysis.sh aggregating astats + ebur128 + volumedetect + silencedetect

This guide covers FFmpeg audio processing. For video operations, see the fundamentals skill. For noise reduction details, see ffmpeg-noise-reduction.