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diff --git a/doc/filters.texi b/doc/filters.texi index f745517..bce20f0 100644 --- a/doc/filters.texi +++ b/doc/filters.texi @@ -701,96 +701,6 @@ tolerance in @file{silence.mp3}: ffmpeg -f lavfi -i amovie=silence.mp3,silencedetect=noise=0.0001 -f null - @end example -@section volume - -Adjust the input audio volume. - -The filter accepts exactly one parameter @var{vol}, which expresses -how the audio volume will be increased or decreased. - -Output values are clipped to the maximum value. - -If @var{vol} is expressed as a decimal number, the output audio -volume is given by the relation: -@example -@var{output_volume} = @var{vol} * @var{input_volume} -@end example - -If @var{vol} is expressed as a decimal number followed by the string -"dB", the value represents the requested change in decibels of the -input audio power, and the output audio volume is given by the -relation: -@example -@var{output_volume} = 10^(@var{vol}/20) * @var{input_volume} -@end example - -Otherwise @var{vol} is considered an expression and its evaluated -value is used for computing the output audio volume according to the -first relation. - -Default value for @var{vol} is 1.0. - -@subsection Examples - -@itemize -@item -Half the input audio volume: -@example -volume=0.5 -@end example - -The above example is equivalent to: -@example -volume=1/2 -@end example - -@item -Decrease input audio power by 12 decibels: -@example -volume=-12dB -@end example -@end itemize - -@section volumedetect - -Detect the volume of the input video. - -The filter has no parameters. The input is not modified. Statistics about -the volume will be printed in the log when the input stream end is reached. - -In particular it will show the mean volume (root mean square), maximum -volume (on a per-sample basis), and the beginning of an histogram of the -registered volume values (from the maximum value to a cumulated 1/1000 of -the samples). - -All volumes are in decibels relative to the maximum PCM value. - -Here is an excerpt of the output: -@example -[Parsed_volumedetect_0 @ 0xa23120] mean_volume: -27 dB -[Parsed_volumedetect_0 @ 0xa23120] max_volume: -4 dB -[Parsed_volumedetect_0 @ 0xa23120] histogram_4db: 6 -[Parsed_volumedetect_0 @ 0xa23120] histogram_5db: 62 -[Parsed_volumedetect_0 @ 0xa23120] histogram_6db: 286 -[Parsed_volumedetect_0 @ 0xa23120] histogram_7db: 1042 -[Parsed_volumedetect_0 @ 0xa23120] histogram_8db: 2551 -[Parsed_volumedetect_0 @ 0xa23120] histogram_9db: 4609 -[Parsed_volumedetect_0 @ 0xa23120] histogram_10db: 8409 -@end example - -It means that: -@itemize -@item -The mean square energy is approximately -27 dB, or 10^-2.7. -@item -The largest sample is at -4 dB, or more precisely between -4 dB and -5 dB. -@item -There are 6 samples at -4 dB, 62 at -5 dB, 286 at -6 dB, etc. -@end itemize - -In other words, raising the volume by +4 dB does not cause any clipping, -raising it by +5 dB causes clipping for 6 samples, etc. - @section asyncts Synchronize audio data with timestamps by squeezing/stretching it and/or dropping samples/adding silence when needed. @@ -919,6 +829,149 @@ out Convert the audio sample format, sample rate and channel layout. This filter is not meant to be used directly. +@section volume + +Adjust the input audio volume. + +The filter accepts exactly one parameter @var{vol}, which expresses +how the audio volume will be increased or decreased. + +Output values are clipped to the maximum value. + +If @var{vol} is expressed as a decimal number, the output audio +volume is given by the relation: +@example +@var{output_volume} = @var{vol} * @var{input_volume} +@end example + +If @var{vol} is expressed as a decimal number followed by the string +"dB", the value represents the requested change in decibels of the +input audio power, and the output audio volume is given by the +relation: +@example +@var{output_volume} = 10^(@var{vol}/20) * @var{input_volume} +@end example + +Otherwise @var{vol} is considered an expression and its evaluated +value is used for computing the output audio volume according to the +first relation. + +Default value for @var{vol} is 1.0. + +@subsection Examples + +@itemize +@item +Half the input audio volume: +@example +volume=0.5 +@end example + +The above example is equivalent to: +@example +volume=1/2 +@end example + +@item +Decrease input audio power by 12 decibels: +@example +volume=-12dB +@end example +@end itemize + +@section volumedetect + +Detect the volume of the input video. + +The filter has no parameters. The input is not modified. Statistics about +the volume will be printed in the log when the input stream end is reached. + +In particular it will show the mean volume (root mean square), maximum +volume (on a per-sample basis), and the beginning of an histogram of the +registered volume values (from the maximum value to a cumulated 1/1000 of +the samples). + +All volumes are in decibels relative to the maximum PCM value. + +Here is an excerpt of the output: +@example +[Parsed_volumedetect_0 @ 0xa23120] mean_volume: -27 dB +[Parsed_volumedetect_0 @ 0xa23120] max_volume: -4 dB +[Parsed_volumedetect_0 @ 0xa23120] histogram_4db: 6 +[Parsed_volumedetect_0 @ 0xa23120] histogram_5db: 62 +[Parsed_volumedetect_0 @ 0xa23120] histogram_6db: 286 +[Parsed_volumedetect_0 @ 0xa23120] histogram_7db: 1042 +[Parsed_volumedetect_0 @ 0xa23120] histogram_8db: 2551 +[Parsed_volumedetect_0 @ 0xa23120] histogram_9db: 4609 +[Parsed_volumedetect_0 @ 0xa23120] histogram_10db: 8409 +@end example + +It means that: +@itemize +@item +The mean square energy is approximately -27 dB, or 10^-2.7. +@item +The largest sample is at -4 dB, or more precisely between -4 dB and -5 dB. +@item +There are 6 samples at -4 dB, 62 at -5 dB, 286 at -6 dB, etc. +@end itemize + +In other words, raising the volume by +4 dB does not cause any clipping, +raising it by +5 dB causes clipping for 6 samples, etc. + +@section volume_justin + +Adjust the input audio volume. + +The filter accepts the following named parameters: +@table @option + +@item volume +Expresses how the audio volume will be increased or decreased. + +Output values are clipped to the maximum value. + +The output audio volume is given by the relation: +@example +@var{output_volume} = @var{volume} * @var{input_volume} +@end example + +Default value for @var{volume} is 1.0. + +@item precision +Mathematical precision. + +This determines which input sample formats will be allowed, which affects the +precision of the volume scaling. + +@table @option +@item fixed +8-bit fixed-point; limits input sample format to U8, S16, and S32. +@item float +32-bit floating-point; limits input sample format to FLT. (default) +@item double +64-bit floating-point; limits input sample format to DBL. +@end table +@end table + +@subsection Examples + +@itemize +@item +Halve the input audio volume: +@example +volume_justin=volume=0.5 +volume_justin=volume=1/2 +volume_justin=volume=-6.0206dB +@end example + +@item +Increase input audio power by 6 decibels using fixed-point precision: +@example +volume_justin=volume=6dB:precision=fixed +@end example +@end itemize + @c man end AUDIO FILTERS @chapter Audio Sources |