How to use FFmpeg for audio processing? What are the common audio filters?

FFmpeg provides powerful audio processing capabilities, including audio extraction, conversion, mixing, noise reduction, and various other operations.

Audio Extraction and Conversion

Extract Audio from Video

bash
# Extract audio stream (no re-encoding)
ffmpeg -i video.mp4 -vn -acodec copy audio.aac

# Extract and convert to MP3
ffmpeg -i video.mp4 -vn -acodec libmp3lame -ab 192k audio.mp3

# Extract and convert to WAV
ffmpeg -i video.mp4 -vn audio.wav

Audio Format Conversion

bash
# MP3 to AAC
ffmpeg -i input.mp3 -c:a aac -b:a 128k output.aac

# WAV to MP3
ffmpeg -i input.wav -c:a libmp3lame -b:a 192k output.mp3

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

Audio Parameter Adjustment

Adjust Volume

bash
# Increase volume (2x)
ffmpeg -i input.mp3 -af "volume=2.0" output.mp3

# Decrease volume (0.5x)
ffmpeg -i input.mp3 -af "volume=0.5" output.mp3

# Adjust using decibels
ffmpeg -i input.mp3 -af "volume=3dB" output.mp3

# Normalize volume
ffmpeg -i input.mp3 -af "loudnorm" output.mp3

Adjust Sample Rate

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

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

# Convert to 16kHz (common for speech recognition)
ffmpeg -i input.wav -ar 16000 output.wav

Adjust Channels

bash
# Convert to mono
ffmpeg -i input.mp3 -ac 1 output.mp3

# Convert to stereo
ffmpeg -i input.mp3 -ac 2 output.mp3

# Extract left channel
ffmpeg -i input.mp3 -af "pan=mono|c0=c0" output.mp3

# Extract right channel
ffmpeg -i input.mp3 -af "pan=mono|c0=c1" output.mp3

Audio Editing

Clip by Time

bash
# Start from 10 seconds, clip 30 seconds
ffmpeg -i input.mp3 -ss 00:00:10 -t 00:00:30 output.mp3

# Start from 1 minute, clip to 3 minutes
ffmpeg -i input.mp3 -ss 00:01:00 -to 00:03:00 output.mp3

# Clip first 60 seconds
ffmpeg -i input.mp3 -t 60 output.mp3

Audio Concatenation

bash
# Concatenate using concat protocol
echo "file 'part1.mp3'" > filelist.txt
echo "file 'part2.mp3'" >> filelist.txt
echo "file 'part3.mp3'" >> filelist.txt
ffmpeg -f concat -safe 0 -i filelist.txt -c copy output.mp3

# Concatenate using concat filter
ffmpeg -i part1.mp3 -i part2.mp3 -i part3.mp3 \
  -filter_complex "[0:a][1:a][2:a]concat=n=3:v=0:a=1[outa]" \
  -map "[outa]" output.mp3

Audio Effects

Fade In/Out

bash
# Fade in for 3 seconds
ffmpeg -i input.mp3 -af "afade=t=in:st=0:d=3" output.mp3

# Fade out for 3 seconds
ffmpeg -i input.mp3 -af "afade=t=out:st=5:d=3" output.mp3

# Fade in and out
ffmpeg -i input.mp3 -af "afade=t=in:st=0:d=3,afade=t=out:st=7:d=3" output.mp3

Audio Mixing

bash
# Mix two audio files
ffmpeg -i audio1.mp3 -i audio2.mp3 -filter_complex "amix=inputs=2:duration=first" output.mp3

# Mix three audio files
ffmpeg -i audio1.mp3 -i audio2.mp3 -i audio3.mp3 \
  -filter_complex "amix=inputs=3:duration=longest" output.mp3

# Adjust mixing ratio
ffmpeg -i audio1.mp3 -i audio2.mp3 \
  -filter_complex "[0:a]volume=0.7[a0];[1:a]volume=0.3[a1];[a0][a1]amix=inputs=2" output.mp3

Audio Delay

bash
# Delay audio by 500 milliseconds
ffmpeg -i input.mp3 -af "adelay=500|500" output.mp3

# Different delay for left and right channels
ffmpeg -i input.mp3 -af "adelay=500|1000" output.mp3

# Advance audio (negative delay)
ffmpeg -i input.mp3 -af "adelay=-200|-200" output.mp3

Audio Noise Reduction

bash
# Remove low frequency noise using highpass filter
ffmpeg -i input.mp3 -af "highpass=f=200" output.mp3

# Remove high frequency noise using lowpass filter
ffmpeg -i input.mp3 -af "lowpass=f=3000" output.mp3

# Use bandpass filter
ffmpeg -i input.mp3 -af "bandpass=f=1000:width_type=h:width=500" output.mp3

Audio Analysis and Processing

Audio Visualization

bash
# Generate audio waveform
ffmpeg -i input.mp3 -filter_complex "showwavespic=s=640x320" waveform.png

# Generate spectrogram
ffmpeg -i input.mp3 -lavfi showspectrumpic=s=640x320 spectrum.png

# Generate audio video
ffmpeg -i input.mp3 -filter_complex "showwaves=s=640x320" output.mp4

View Audio Information

bash
# View detailed audio information
ffmpeg -i input.mp3 -hide_banner

# View audio sample rate, bitrate, etc.
ffprobe -i input.mp3 -show_streams -select_streams a

# Analyze audio volume
ffmpeg -i input.mp3 -af "volumedetect" -f null -

Advanced Audio Processing

Audio Speed Change

bash
# Speed up 1.5x
ffmpeg -i input.mp3 -filter:a "atempo=1.5" output.mp3

# Slow down 0.75x
ffmpeg -i input.mp3 -filter:a "atempo=0.75" output.mp3

# Large speed change (requires multiple atempo)
ffmpeg -i input.mp3 -filter:a "atempo=2.0,atempo=2.0" output.mp3

Audio Pitch Change

bash
# Increase pitch (semitone)
ffmpeg -i input.mp3 -filter:a "asetrate=44100*1.05946" output.mp3

# Decrease pitch (semitone)
ffmpeg -i input.mp3 -filter:a "asetrate=44100*0.94387" output.mp4

Audio Echo

bash
# Add echo effect
ffmpeg -i input.mp3 -af "aecho=0.8:0.9:1000:0.3" output.mp3

Audio Encoding Parameters

Common Audio Encoders

bash
# AAC encoding
ffmpeg -i input.wav -c:a aac -b:a 128k output.aac

# MP3 encoding
ffmpeg -i input.wav -c:a libmp3lame -b:a 192k output.mp3

# Opus encoding (high quality)
ffmpeg -i input.wav -c:a libopus -b:a 128k output.opus

# FLAC encoding (lossless)
ffmpeg -i input.wav -c:a flac output.flac

Audio Quality Settings

bash
# High quality MP3 (320kbps)
ffmpeg -i input.wav -c:a libmp3lame -b:a 320k output.mp3

# Medium quality MP3 (192kbps)
ffmpeg -i input.wav -c:a libmp3lame -b:a 192k output.mp3

# Low quality MP3 (128kbps)
ffmpeg -i input.wav -c:a libmp3lame -b:a 128k output.mp3

# VBR encoding (variable bitrate)
ffmpeg -i input.wav -c:a libmp3lame -q:a 2 output.mp3

When processing audio, it is recommended to use lossless formats (such as WAV, FLAC) for intermediate processing, and finally convert to lossy formats to reduce quality loss.