Ffmpeg Audio Processing

Volume Adjustment

# 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

# 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

# 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

# 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

# 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

# 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

# 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

# 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