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
| Task | Command |
|---|---|
| Extract audio | ffmpeg -i video.mp4 -vn -c:a copy audio.m4a |
| Convert to MP3 | ffmpeg -i input.flac -c:a libmp3lame -q:a 2 output.mp3 |
| Normalize (EBU R128) | -af loudnorm=I=-23:LRA=7:TP=-2 |
| Podcast standard | -af loudnorm=I=-16:TP=-1.5 |
| Adjust volume | -af "volume=1.5" or -af "volume=6dB" |
| Mono to stereo | -ac 2 |
| Codec | Recommended Bitrate | Use Case |
|---|---|---|
| AAC | 128-192k (music), 64k (speech) | Streaming, mobile |
| MP3 | 192-320k (music), 128k (speech) | Universal compatibility |
| Opus | 96-128k (music), 48k (speech) | WebM, VoIP, modern |
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
| Codec | Encoder | Bitrate Range | Quality | Compatibility | Use Case |
|---|---|---|---|---|---|
| AAC | aac, libfdk_aac | 64-320 kbps | Excellent | Universal | Streaming, mobile |
| MP3 | libmp3lame | 96-320 kbps | Good | Universal | Legacy, podcasts |
| Opus | libopus | 32-256 kbps | Best | Modern | VoIP, WebM |
| FLAC | flac | ~900 kbps | Lossless | Wide | Archival |
| ALAC | alac | ~900 kbps | Lossless | Apple | Apple ecosystem |
| Vorbis | libvorbis | 64-500 kbps | Very Good | Wide | WebM, games |
| AC3 | ac3 | 192-640 kbps | Good | Universal | DVD, Blu-ray |
| EAC3 | eac3 | 192-768 kbps | Very Good | Wide | Streaming |
| xHE-AAC | - (decode only) | 12-64 kbps | Excellent | Emerging | Ultra-low bitrate |
Recommended Bitrates
| Use Case | AAC | MP3 | Opus |
|---|---|---|---|
| Podcast/Speech | 64-96k | 96-128k | 48-64k |
| Music (Standard) | 128-192k | 192-256k | 96-128k |
| Music (High Quality) | 256-320k | 320k | 160-256k |
| Transparent Quality | 256k+ | 320k | 192k+ |
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
| Standard | Target | TP (True Peak) | Use Case |
|---|---|---|---|
| EBU R128 | -23 LUFS | -1 dBTP | European broadcast |
| ATSC A/85 | -24 LKFS | -2 dBTP | US broadcast |
| Spotify | -14 LUFS | -1 dBTP | Streaming |
| YouTube | -14 LUFS | -1 dBTP | Video platform |
| Apple Music | -16 LUFS | -1 dBTP | Music streaming |
| Podcast | -16 to -19 LUFS | -1 dBTP | Podcast |
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
Podcast Processing
# Complete podcast processing chain
ffmpeg -i raw_podcast.wav \
-af "highpass=f=80,\
acompressor=threshold=-20dB:ratio=4:attack=5:release=50,\
loudnorm=I=-16:TP=-1.5:LRA=11,\
silenceremove=start_periods=1:start_silence=1:start_threshold=-50dB" \
-c:a aac -b:a 96k \
podcast.m4a
Music Mastering Chain
# Mastering chain
ffmpeg -i mix.wav \
-af "equalizer=f=60:width_type=o:width=1:g=1,\
equalizer=f=12000:width_type=o:width=1:g=0.5,\
acompressor=threshold=-12dB:ratio=2:attack=20:release=200,\
alimiter=limit=0.95,\
loudnorm=I=-14:TP=-1:LRA=9" \
-c:a flac \
master.flac
Broadcast Normalization
# EBU R128 broadcast compliance ffmpeg -i input.wav \ -af "loudnorm=I=-23:TP=-1:LRA=11:dual_mono=true" \ -ar 48000 \ -c:a pcm_s24le \ broadcast.wav
Troubleshooting
Common Issues
"loudnorm resamples to 192kHz"
# Force output sample rate ffmpeg -i input.mp3 \ -af loudnorm=I=-16:TP=-1.5:LRA=11 \ -ar 48000 \ output.mp3
Audio/video sync after processing
# Maintain sync with video ffmpeg -i video.mp4 \ -af "loudnorm=I=-16:TP=-1.5:LRA=11,aresample=async=1" \ -c:v copy \ output.mp4
Quality loss from re-encoding
- •Use lossless intermediate format (FLAC, WAV)
- •Avoid multiple lossy conversions
- •Use high bitrates for final lossy encode
Audio Analysis & Measurement
Audio Statistics (astats)
Measure comprehensive audio statistics including RMS, peak levels, crest factor, bit depth, and DC offset.
# Full audio statistics ffmpeg -i input.mp3 -af "astats=metadata=1:reset=1" -f null - # Output includes: # - RMS level and peak level # - Crest factor # - Dynamic range # - DC offset # - Min/Max sample values # - Number of samples # Per-channel statistics ffmpeg -i input.mp3 -af "astats=metadata=1:reset=1:measure_perchannel=all" -f null - # Measure specific metrics ffmpeg -i input.mp3 -af "astats=measure_overall=RMS_level+Peak_level:reset=1" -f null -
astats Metrics:
| Metric | Description |
|---|---|
DC_offset | DC bias in signal |
Min_level | Minimum sample value |
Max_level | Maximum sample value |
Min_difference | Minimum sample-to-sample difference |
Max_difference | Maximum sample-to-sample difference |
Mean_difference | Average sample-to-sample difference |
RMS_level | Root Mean Square level (dB) |
Peak_level | Peak level (dB) |
RMS_peak | RMS peak level |
RMS_trough | RMS trough level |
Crest_factor | Peak to RMS ratio |
Flat_factor | Flatness measure |
Peak_count | Number of samples at peak |
Bit_depth | Actual bit depth used |
Dynamic_range | Dynamic range in dB |
EBU R128 Loudness Measurement (ebur128)
Comprehensive loudness measurement per EBU R128 / ITU-R BS.1770 standards.
# Basic loudness measurement ffmpeg -i input.mp3 -af "ebur128=peak=true" -f null - # Output includes: # - Momentary loudness (M) # - Short-term loudness (S) # - Integrated loudness (I) # - Loudness Range (LRA) # - True Peak (dBTP) # Frame-by-frame measurement ffmpeg -i input.mp3 -af "ebur128=framelog=verbose:peak=true" -f null - 2>&1 | grep Summary # Generate loudness graph (PNG) ffmpeg -i input.mp3 \ -filter_complex "ebur128=video=1:meter=18:gauge=1[v];[v]scale=1280:720[out]" \ -map "[out]" \ -frames:v 1 \ loudness_graph.png # Create loudness monitoring video ffmpeg -i input.mp3 \ -filter_complex "ebur128=video=1:meter=18:gauge=1:scale=absolute[v]" \ -map "[v]" -map 0:a \ -c:a copy \ loudness_monitor.mp4 # Measure with dual mono (speech) ffmpeg -i input.mp3 -af "ebur128=dualmono=1:peak=true" -f null -
ebur128 Parameters:
| Parameter | Description | Values |
|---|---|---|
video | Generate video output | 0 or 1 |
meter | Loudness meter level | 9, 12, 18 |
gauge | Show gauge overlay | 0 or 1 |
scale | Scale type | absolute, relative |
peak | Measure true peak | true, sample, none |
dualmono | Dual mono mode | 0 or 1 |
framelog | Logging level | quiet, info, verbose |
Speech Normalization (speechnorm)
Specialized normalizer for speech content that adapts to dynamic speech patterns.
# Basic speech normalization ffmpeg -i speech.mp3 -af "speechnorm" output.mp3 # Speech normalization with custom parameters ffmpeg -i speech.mp3 \ -af "speechnorm=p=0.95:m=10:r=0.0005:l=1" \ output.mp3 # Aggressive speech normalization ffmpeg -i speech.mp3 \ -af "speechnorm=p=0.9:e=15:r=0.001:l=1" \ output.mp3 # Podcast processing with speech normalization ffmpeg -i podcast.wav \ -af "highpass=f=80,speechnorm=p=0.95:e=12.5:r=0.0005,loudnorm=I=-16:TP=-1.5" \ -c:a aac -b:a 96k \ podcast.m4a
speechnorm Parameters:
| Parameter | Description | Default | Range |
|---|---|---|---|
p | Peak value target | 0.95 | 0-1 |
e | Expansion factor | 12.5 | 1-50 |
r | Rise time (speed of increase) | 0.0005 | 0-1 |
f | Fall time (speed of decrease) | 0.001 | 0-1 |
c | Compression factor | 0 | 0-1 |
l | Link channels | 0 | 0 or 1 |
Dialogue Enhancement (dialoguenhance) - FFmpeg 8.0+
Enhance dialogue clarity by separating and boosting voice frequencies.
# Basic dialogue enhancement ffmpeg -i input.mp4 -af "dialoguenhance" -c:v copy output.mp4 # Custom dialogue enhancement ffmpeg -i input.mp4 \ -af "dialoguenhance=original=0.3:enhance=0.7:voice=0.8" \ -c:v copy output.mp4 # Heavy enhancement for poor recordings ffmpeg -i input.mp4 \ -af "dialoguenhance=original=0.2:enhance=0.9" \ -c:v copy output.mp4
dialoguenhance Parameters:
| Parameter | Description | Default | Range |
|---|---|---|---|
original | Original signal mix | 1 | 0-1 |
enhance | Enhanced signal mix | 1 | 0-1 |
voice | Voice clarity boost | 2 | 2-32 |
3D Audio / Binaural (sofalizer)
Apply HRTF (Head-Related Transfer Function) for 3D audio and binaural processing using SOFA files.
# Basic binaural conversion (requires SOFA file) ffmpeg -i surround.ac3 \ -af "sofalizer=sofa=/path/to/hrtf.sofa" \ binaural.mp3 # With custom gain and rotation ffmpeg -i surround.ac3 \ -af "sofalizer=sofa=/path/to/hrtf.sofa:gain=0:rotation=0" \ binaural.mp3 # Binaural conversion with elevation ffmpeg -i surround.ac3 \ -af "sofalizer=sofa=/path/to/hrtf.sofa:elevation=0:radius=1" \ binaural.mp3
SOFA Files:
- •Download HRTF databases from: https://sofacoustics.org/data/database/
- •Common formats: CIPIC, MIT KEMAR, LISTEN databases
sofalizer Parameters:
| Parameter | Description | Range |
|---|---|---|
sofa | Path to SOFA file | - |
gain | Additional gain (dB) | -20 to 40 |
rotation | Head rotation (degrees) | -360 to 360 |
elevation | Head elevation (degrees) | -90 to 90 |
radius | Distance scaling | 0 to 3 |
type | Interpolation type | time, freq |
Volume Detection
# Detect volume levels ffmpeg -i input.mp3 -af "volumedetect" -f null - # Output includes: # - mean_volume (average) # - max_volume (peak) # - histogram data
A-Weighting (aweighting)
Apply A-weighting curve for perceived loudness measurement.
# Apply A-weighting filter ffmpeg -i input.mp3 -af "aweighting" output_aweighted.wav # Measure A-weighted levels ffmpeg -i input.mp3 -af "aweighting,astats=measure_overall=RMS_level" -f null -
Audio Fingerprinting (chromaprint)
Generate audio fingerprints for identification.
# Generate chromaprint fingerprint ffmpeg -i input.mp3 -f chromaprint -fp_format raw fingerprint.txt # Generate Base64 fingerprint ffmpeg -i input.mp3 -f chromaprint -fp_format base64 - 2>&1 | grep FINGERPRINT
Complete Analysis Workflow
#!/bin/bash # audio-analysis.sh - Complete audio analysis INPUT="$1" echo "=== Audio Analysis Report ===" echo "File: $INPUT" echo "" echo "--- Basic Statistics ---" ffmpeg -i "$INPUT" -af "astats=measure_overall=all" -f null - 2>&1 | grep -A 50 "Parsed_astats" echo "" echo "--- Loudness (EBU R128) ---" ffmpeg -i "$INPUT" -af "ebur128=peak=true" -f null - 2>&1 | grep -E "(Summary|I:|LRA:|Peak:)" echo "" echo "--- Volume Detection ---" ffmpeg -i "$INPUT" -af "volumedetect" -f null - 2>&1 | grep -E "(mean_volume|max_volume)" echo "" echo "--- Silence Detection ---" ffmpeg -i "$INPUT" -af "silencedetect=noise=-50dB:d=0.5" -f null - 2>&1 | grep silence
This guide covers FFmpeg audio processing. For video operations, see the fundamentals skill. For noise reduction details, see ffmpeg-noise-reduction.