I want to detect silence or delay in audio for a given duration file and remove it. For example, if someone started speaking and then paused for some duration to think.
There's this question but it only detects the silence at the end and doesn't remove it. My colleague suggested sox but I'm not sure if it's the best tool for the job nor how to use it frankly, moreover, the project died in 2015.
The Sox man page describes this in detail.
silence [-l] above-periods [duration threshold[d|%]
[below-periods duration threshold[d|%]]
if we start with a sample command:
sox input.mp3 out.mp3 -S silence -l 1 0.2 1% -1 0.2 1%
`-S` - show progress
`silence` - the filter
`-l` - leave x amount of each silence in tact
`1` - trim from 1st silence [above-periods]
`0.2` - amount of each silence to leave untouched [duration]
`1%` - test for near absolute (0%) silence [threshold]
`-1` - trim silence from the middle of the file [below-periods]
`0.2` - amount of each silence to leave untouched [duration]
`1%` - test for near absolute (0%) silence [threshold]
The detail courtesy of Sox:
silence [-l] above-periods [duration threshold[d|%]
[below-periods duration threshold[d|%]]
Removes silence from the beginning, middle, or end of the audio. `Si‐
lence' is determined by a specified threshold.
The above-periods value is used to indicate if audio should be trimmed at
the beginning of the audio. A value of zero indicates no silence should
be trimmed from the beginning. When specifying a non-zero above-periods,
it trims audio up until it finds non-silence. Normally, when trimming si‐
lence from beginning of audio the above-periods will be 1 but it can be
increased to higher values to trim all audio up to a specific count of
non-silence periods. For example, if you had an audio file with two songs
that each contained 2 seconds of silence before the song, you could spec‐
ify an above-period of 2 to strip out both silence periods and the first
song.
When above-periods is non-zero, you must also specify a duration and
threshold. duration indicates the amount of time that non-silence must be
detected before it stops trimming audio. By increasing the duration,
burst of noise can be treated as silence and trimmed off.
threshold is used to indicate what sample value you should treat as si‐
lence. For digital audio, a value of 0 may be fine but for audio
recorded from analog, you may wish to increase the value to account for
background noise.
When optionally trimming silence from the end of the audio, you specify a
below-periods count. In this case, below-period means to remove all au‐
dio after silence is detected. Normally, this will be a value 1 of but
it can be increased to skip over periods of silence that are wanted. For
example, if you have a song with 2 seconds of silence in the middle and 2
second at the end, you could set below-period to a value of 2 to skip
over the silence in the middle of the audio.
For below-periods, duration specifies a period of silence that must exist
before audio is not copied any more. By specifying a higher duration,
silence that is wanted can be left in the audio. For example, if you
have a song with an expected 1 second of silence in the middle and 2 sec‐
onds of silence at the end, a duration of 2 seconds could be used to skip
over the middle silence.
Unfortunately, you must know the length of the silence at the end of your
audio file to trim off silence reliably. A workaround is to use the si‐
lence effect in combination with the reverse effect. By first reversing
the audio, you can use the above-periods to reliably trim all audio from
what looks like the front of the file. Then reverse the file again to
get back to normal.
To remove silence from the middle of a file, specify a below-periods that
is negative. This value is then treated as a positive value and is also
used to indicate that the effect should restart processing as specified
by the above-periods, making it suitable for removing periods of silence
in the middle of the audio.
The option -l indicates that below-periods duration length of audio
should be left intact at the beginning of each period of silence. For
example, if you want to remove long pauses between words but do not want
to remove the pauses completely.
duration is a time specification with the peculiarity that a bare number
is interpreted as a sample count, not as a number of seconds. For speci‐
fying seconds, either use the t suffix (as in `2t') or specify minutes,
too (as in `0:02').
threshold numbers may be suffixed with d to indicate the value is in
decibels, or % to indicate a percentage of maximum value of the sample
value (0% specifies pure digital silence).
Finally, a python sample code, to enable monitoring of the output:
try:
self.comm = Popen(['sox', self.orig_file, self.new_file, '-S', 'silence',\
'-l', '1', '0.1', '1%', '-1', str(self.secs.GetValue()), '1%'],\
stdout=PIPE, stderr=STDOUT, universal_newlines=True)
except Exception as e:
......
It's worth pointing out that ffmpeg has the filters silencedetect and silenceremove.
While I do use silencedetect e.g.:
ffmpeg -hide_banner -stats -i interview.wav -af silencedetect=noise=0dB:d=3 -vn -sn -dn -f null -
silenceremove e.g.:
ffmpeg -hide_banner -v quiet -i interview.wav -af silenceremove=stop_periods=-1:stop_duration=2:stop_threshold=-3dB -vn -sn -dn -f wav - | ffplay -hide_banner -v quiet -autoexit -i -
I've found to be less dependable.
It should also be pointed out, that silence is notoriously difficult to pin down, except on an individual/ad-hoc basis, due to background noise.