Audio Filtering

Table of Contents

• afade
  • Implementation
  • Examples
  • Resources

afade

The afade audio filter allows us to apply fade-in/out effect to input audio. This can be useful in removing stray noise or in isolating the track if we do not have a clean place to start or end our cuts.

Implementation

We will apply the afade filter in our second pass after normalization. Our argument is formatted as follows:

-af "loudnorm=I=-16:LRA=20:TP=-1:dual_mono=true:linear=true:print_format=json:measured_I=#.##:measured_LRA=#.##:measured_TP=#.##:measured_thresh=#.##:offset=#.##,afade=..."

d specifies the duration of the effect

curve specifies the fade transition curve. See Resources for a visual reference guide.

st specifies the start time of the fade effect

Remark

The values for d and st are relative to the start position of the encode in fast seek mode.

For example, if our start position is 00:00.960 and we are applying a fade in of duration 0.500 starting at the position 00:00.960, our d is 0.500 and our st is 0, or unset.

The values for st are the positions in the source file in slow seek mode.

For example, if the start position is 00:00.960 and we are applying a fade in of duration 0.500 starting at the position 00:00.960, our d is 0.500 and our st is 0.960.

Examples

Fade-in of .300s where we are attempting to isolate the track from stray noise present from the position of the first frame to the start of the track.

-af "loudnorm=I=-16:LRA=20:TP=-1:dual_mono=true:linear=true:print_format=json:measured_I=-20.11:measured_LRA=9.20:measured_TP=-12.03:measured_thresh=-30.43:offset=-2.11,afade=d=0.300:curve=exp"

Without afade filter | With afade filter

Fade-out of .500s where the track does not cleanly stop on the ending position we've chosen. The duration of the encode is exactly 90s.

-af "loudnorm=I=-16:LRA=20:TP=-1:dual_mono=true:linear=true:print_format=json:measured_I=-20.11:measured_LRA=9.20:measured_TP=-12.03:measured_thresh=-30.43:offset=-2.11,afade=t=out:st=89.500:d=0.500"

Without afade filter | With afade filter

Resources

FFmpeg afade (audio fade filter) curves cheatsheet