Audio Fade-In and Fade-Out with the afade Filter

Q: Why does my fade start too early?

Check the `st=` (start time) parameter — fades default to 0. To fade out at the end of the file, compute `start = duration − fade_length` and pass it explicitly.

What You’ll Learn

How to apply fade-in and fade-out with the afade filter
The meaning of t (type), st (start time), and d (duration)
Differences between curve types (tri, sin, exp, etc.)
How to apply fades to the audio track of a video file
How to combine fade-in and fade-out in a single command

Tested with: FFmpeg 6.1 (verified on ubuntu-latest / CI) Platform: Windows / macOS / Linux

Basic Commands

Fade-in (gradually ramp up at the start)

ffmpeg -i input.mp3 -af "afade=t=in:st=0:d=3" output.mp3

Parameter	Value	Description
`t=in`	—	Fade in
`st=0`	0 s	Fade start time
`d=3`	3 s	Fade duration

Fade-out (gradually ramp down at the end)

First check the length of the audio:

ffmpeg -i input.mp3 -f null /dev/null 2>&1 | grep Duration

Fade out over the last 10 seconds of a 60-second file:

ffmpeg -i input.mp3 -af "afade=t=out:st=50:d=10" output.mp3

Parameter	Value	Description
`t=out`	—	Fade out
`st=50`	50 s	Fade start time
`d=10`	10 s	Fade duration

Applying Fade-In and Fade-Out Together

Chain multiple filters with a comma inside -af:

ffmpeg -i input.mp3 -af "afade=t=in:st=0:d=3,afade=t=out:st=50:d=10" output.mp3

Curve Types

Use the curve option to change the shape of the fade:

ffmpeg -i input.mp3 -af "afade=t=in:st=0:d=3:curve=qsin" output.mp3

Curve	Description
`tri`	Linear (triangular). The default
`qsin`	Quarter sine wave. Natural-sounding
`hsin`	Half sine wave. Smoother S-shape
`exp`	Exponential. Changes sharply
`log`	Logarithmic. Starts sharply, ends gently

Apply Fades to the Audio Track of a Video File

ffmpeg -i input.mp4 -af "afade=t=in:st=0:d=2" -c:v copy output.mp4

-c:v copy keeps the video untouched and only re-encodes the audio.

Combine with Video Fades

Apply a matching video fade (fade) alongside the audio fade (afade):

ffmpeg -i input.mp4 -vf "fade=t=in:st=0:d=2" -af "afade=t=in:st=0:d=2" -c:a aac output.mp4

Common Pitfalls

Match `st` to the actual audio length for fade-out

If st + d goes past the end of the track FFmpeg will not error out, but the fade will be truncated. Check the duration first if the fade sounds cut short.

Combine with `-c:v copy` to re-encode only the audio

When the video doesn’t need any changes, -c:v copy preserves its quality and only the audio is re-encoded.

Frequently Asked Questions

What is the difference between afade and acrossfade?

afade fades a single track in or out, while acrossfade blends two tracks over a transition window. For BGM swaps, use acrossfade; for opener/closer fades, use afade.

How long should the fade be?

Speech: 0.3–0.5 s in, 1–2 s out. Music: 1–2 s in, 2–4 s out. Anything shorter than 100 ms can pop on cheaper speakers.

Can I fade only specific frequencies?

afade affects the whole signal. For frequency-selective fading you would chain a band filter (e.g. lowpass) before the fade.

Why does my fade start too early?

Check the st= (start time) parameter — fades default to 0. To fade out at the end of the file, compute start = duration − fade_length and pass it explicitly.

Does afade re-encode the file?

Yes — any audio filter forces re-encoding of the audio track. Video can stay copy-only by using -c:v copy alongside.

Volume Level Detection — check peak and average loudness with volumedetect
Extract Audio — use -vn to pull audio out of a video

Tested with ffmpeg 6.1 / Ubuntu 24.04 (GitHub Actions runner) Primary sources: ffmpeg.org/ffmpeg-filters.html#afade / trac.ffmpeg.org/wiki/AudioVolume