Adjust the input audio volume.
It accepts the following parameters:
- volume
-
Set audio volume expression.
Output values are clipped to the maximum value.
The output audio volume is given by the relation:
output_volume = volume * input_volume
The default value for volume is "1.0".
- precision
-
This parameter represents the mathematical precision.
It determines which input sample formats will be allowed, which affects the precision of the volume scaling.
- fixed
-
8-bit fixed-point; this limits input sample format to U8, S16, and S32.
- float
-
32-bit floating-point; this limits input sample format to FLT. (default)
- double
-
64-bit floating-point; this limits input sample format to DBL.
- replaygain
-
Choose the behaviour on encountering ReplayGain side data in input frames.
- drop
-
Remove ReplayGain side data, ignoring its contents (the default).
- ignore
-
Ignore ReplayGain side data, but leave it in the frame.
- track
-
Prefer the track gain, if present.
- album
-
Prefer the album gain, if present.
- replaygain_preamp
-
Pre-amplification gain in dB to apply to the selected replaygain gain.
Default value for replaygain_preamp is 0.0.
- replaygain_noclip
-
Prevent clipping by limiting the gain applied.
Default value for replaygain_noclip is 1.
- eval
-
Set when the volume expression is evaluated.
It accepts the following values:
- once
-
only evaluate expression once during the filter initialization, or when the volume command is sent
- frame
-
evaluate expression for each incoming frame
Default value is once.
The volume expression can contain the following parameters.
- n
-
frame number (starting at zero)
- nb_channels
-
number of channels
- nb_consumed_samples
-
number of samples consumed by the filter
- nb_samples
-
number of samples in the current frame
- pos
-
original frame position in the file
- pts
-
frame PTS
- sample_rate
-
sample rate
- startpts
-
PTS at start of stream
- startt
-
time at start of stream
- t
-
frame time
- tb
-
timestamp timebase
- volume
-
last set volume value
Note that when eval is set to once only the sample_rate and tb variables are available, all other variables will evaluate to NAN.
Commands
This filter supports the following commands:
- volume
-
Modify the volume expression. The command accepts the same syntax of the corresponding option.
If the specified expression is not valid, it is kept at its current value.
Examples
-
Halve the input audio volume:
volume=volume=0.5 volume=volume=1/2 volume=volume=-6.0206dB
In all the above example the named key for volume can be omitted, for example like in:
volume=0.5
-
Increase input audio power by 6 decibels using fixed-point precision:
volume=volume=6dB:precision=fixed
-
Fade volume after time 10 with an annihilation period of 5 seconds:
volume='if(lt(t,10),1,max(1-(t-10)/5,0))':eval=frame