AUDIO FILTERS
=============

Audio filters allow you to modify the audio stream and its properties. The
syntax is:

``--af=...``
    Setup a chain of audio filters. See ``--vf`` for the syntax.

.. note::

    To get a full list of available audio filters, see ``--af=help``.

    Also, keep in mind that most actual filters are available via the ``lavfi``
    wrapper, which gives you access to most of libavfilter's filters. This
    includes all filters that have been ported from MPlayer to libavfilter.

See ``--vf`` group of options for info on how ``--af-defaults``, ``--af-add``,
``--af-pre``, ``--af-del``, ``--af-clr``, and possibly others work.

Available filters are:

``lavrresample[=option1:option2:...]``
    This filter uses libavresample (or libswresample, depending on the build)
    to change sample rate, sample format, or channel layout of the audio stream.
    This filter is automatically enabled if the audio output does not support
    the audio configuration of the file being played.

    It supports only the following sample formats: u8, s16, s32, float.

    ``filter-size=<length>``
        Length of the filter with respect to the lower sampling rate. (default:
        16)
    ``phase-shift=<count>``
        Log2 of the number of polyphase entries. (..., 10->1024, 11->2048,
        12->4096, ...) (default: 10->1024)
    ``cutoff=<cutoff>``
        Cutoff frequency (0.0-1.0), default set depending upon filter length.
    ``linear``
        If set then filters will be linearly interpolated between polyphase
        entries. (default: no)
    ``no-detach``
        Do not detach if input and output audio format/rate/channels match.
        (If you just want to set defaults for this filter that will be used
        even by automatically inserted lavrresample instances, you should
        prefer setting them with ``--af-defaults=lavrresample:...``.)
    ``normalize=<yes|no|auto>``
        Whether to normalize when remixing channel layouts (default: auto).
        ``auto`` uses the value set by ``--audio-normalize-downmix``.
    ``o=<string>``
        Set AVOptions on the SwrContext or AVAudioResampleContext. These should
        be documented by FFmpeg or Libav.

``lavcac3enc[=options]``
    Encode multi-channel audio to AC-3 at runtime using libavcodec. Supports
    16-bit native-endian input format, maximum 6 channels. The output is
    big-endian when outputting a raw AC-3 stream, native-endian when
    outputting to S/PDIF. If the input sample rate is not 48 kHz, 44.1 kHz or
    32 kHz, it will be resampled to 48 kHz.

    ``tospdif=<yes|no>``
        Output raw AC-3 stream if ``no``, output to S/PDIF for
        pass-through if ``yes`` (default).

    ``bitrate=<rate>``
        The bitrate use for the AC-3 stream. Set it to 384 to get 384 kbps.

        The default is 640. Some receivers might not be able to handle this.

        Valid values: 32, 40, 48, 56, 64, 80, 96, 112, 128,
        160, 192, 224, 256, 320, 384, 448, 512, 576, 640.

        The special value ``auto`` selects a default bitrate based on the
        input channel number:

        :1ch: 96
        :2ch: 192
        :3ch: 224
        :4ch: 384
        :5ch: 448
        :6ch: 448

    ``minch=<n>``
        If the input channel number is less than ``<minch>``, the filter will
        detach itself (default: 3).

    ``encoder=<name>``
        Select the libavcodec encoder used. Currently, this should be an AC-3
        encoder, and using another codec will fail horribly.

``equalizer=g1:g2:g3:...:g10``
    10 octave band graphic equalizer, implemented using 10 IIR band-pass
    filters. This means that it works regardless of what type of audio is
    being played back. The center frequencies for the 10 bands are:

    === ==========
    No. frequency
    === ==========
    0    31.25  Hz
    1    62.50  Hz
    2   125.00  Hz
    3   250.00  Hz
    4   500.00  Hz
    5     1.00 kHz
    6     2.00 kHz
    7     4.00 kHz
    8     8.00 kHz
    9    16.00 kHz
    === ==========

    If the sample rate of the sound being played is lower than the center
    frequency for a frequency band, then that band will be disabled. A known
    bug with this filter is that the characteristics for the uppermost band
    are not completely symmetric if the sample rate is close to the center
    frequency of that band. This problem can be worked around by upsampling
    the sound using a resampling filter before it reaches this filter.

    ``<g1>:<g2>:<g3>:...:<g10>``
        floating point numbers representing the gain in dB for each frequency
        band (-12-12)

    .. admonition:: Example

        ``mpv --af=equalizer=11:11:10:5:0:-12:0:5:12:12 media.avi``
            Would amplify the sound in the upper and lower frequency region
            while canceling it almost completely around 1 kHz.

``channels=nch[:routes]``
    Can be used for adding, removing, routing and copying audio channels. If
    only ``<nch>`` is given, the default routing is used. It works as follows:
    If the number of output channels is greater than the number of input
    channels, empty channels are inserted (except when mixing from mono to
    stereo; then the mono channel is duplicated). If the number of output
    channels is less than the number of input channels, the exceeding
    channels are truncated.

    ``<nch>``
        number of output channels (1-8)
    ``<routes>``
        List of ``,`` separated routes, in the form ``from1-to1,from2-to2,...``.
        Each pair defines where to route each channel. There can be at most
        8 routes. Without this argument, the default routing is used. Since
        ``,`` is also used to separate filters, you must quote this argument
        with ``[...]`` or similar.

    .. admonition:: Examples

        ``mpv --af=channels=4:[0-1,1-0,2-2,3-3] media.avi``
            Would change the number of channels to 4 and set up 4 routes that
            swap channel 0 and channel 1 and leave channel 2 and 3 intact.
            Observe that if media containing two channels were played back,
            channels 2 and 3 would contain silence but 0 and 1 would still be
            swapped.

        ``mpv --af=channels=6:[0-0,0-1,0-2,0-3] media.avi``
            Would change the number of channels to 6 and set up 4 routes that
            copy channel 0 to channels 0 to 3. Channel 4 and 5 will contain
            silence.

    .. note::

        You should probably not use this filter. If you want to change the
        output channel layout, try the ``format`` filter, which can make mpv
        automatically up- and downmix standard channel layouts.

``format=format:srate:channels:out-format:out-srate:out-channels``
    Does not do any format conversion itself. Rather, it may cause the
    filter system to insert necessary conversion filters before or after this
    filter if needed. It is primarily useful for controlling the audio format
    going into other filters. To specify the format for audio output, see
    ``--audio-format``, ``--audio-samplerate``, and ``--audio-channels``. This
    filter is able to force a particular format, whereas ``--audio-*``
    may be overridden by the ao based on output compatibility.

    All parameters are optional. The first 3 parameters restrict what the filter
    accepts as input. They will therefore cause conversion filters to be
    inserted before this one.  The ``out-`` parameters tell the filters or audio
    outputs following this filter how to interpret the data without actually
    doing a conversion. Setting these will probably just break things unless you
    really know you want this for some reason, such as testing or dealing with
    broken media.

    ``<format>``
        Force conversion to this format. Use ``--af=format=format=help`` to get
        a list of valid formats.

    ``<srate>``
        Force conversion to a specific sample rate. The rate is an integer,
        48000 for example.

    ``<channels>``
        Force mixing to a specific channel layout. See ``--audio-channels`` option
        for possible values.

    ``<out-format>``

    ``<out-srate>``

    ``<out-channels>``

    *NOTE*: this filter used to be named ``force``. The old ``format`` filter
    used to do conversion itself, unlike this one which lets the filter system
    handle the conversion.

``volume[=<volumedb>[:...]]``
    Implements software volume control. Use this filter with caution since it
    can reduce the signal to noise ratio of the sound. In most cases it is
    best to use the *Master* volume control of your sound card or the volume
    knob on your amplifier.

    *NOTE*: This filter is not reentrant and can therefore only be enabled
    once for every audio stream.

    ``<volumedb>``
        Sets the desired gain in dB for all channels in the stream from -200 dB
        to +60 dB, where -200 dB mutes the sound completely and +60 dB equals a
        gain of 1000 (default: 0).
    ``replaygain-track``
        Adjust volume gain according to the track-gain replaygain value stored
        in the file metadata.
    ``replaygain-album``
        Like replaygain-track, but using the album-gain value instead.
    ``replaygain-preamp``
        Pre-amplification gain in dB to apply to the selected replaygain gain
        (default: 0).
    ``replaygain-clip=yes|no``
        Prevent clipping caused by replaygain by automatically lowering the
        gain (default). Use ``replaygain-clip=no`` to disable this.
    ``replaygain-fallback``
        Gain in dB to apply if the file has no replay gain tags. This option
        is always applied if the replaygain logic is somehow inactive. If this
        is applied, no other replaygain options are applied.
    ``softclip``
        Turns soft clipping on. Soft-clipping can make the
        sound more smooth if very high volume levels are used. Enable this
        option if the dynamic range of the loudspeakers is very low.

        *WARNING*: This feature creates distortion and should be considered a
        last resort.
    ``s16``
        Force S16 sample format if set. Lower quality, but might be faster
        in some situations.
    ``detach``
        Remove the filter if the volume is not changed at audio filter config
        time. Useful with replaygain: if the current file has no replaygain
        tags, then the filter will be removed if this option is enabled.
        (If ``--softvol=yes`` is used and the player volume controls are used
        during playback, a different volume filter will be inserted.)

    .. admonition:: Example

        ``mpv --af=volume=10.1 media.avi``
            Would amplify the sound by 10.1 dB and hard-clip if the sound level
            is too high.

``pan=n:[<matrix>]``
    Mixes channels arbitrarily. Basically a combination of the volume and the
    channels filter that can be used to down-mix many channels to only a few,
    e.g. stereo to mono, or vary the "width" of the center speaker in a
    surround sound system. This filter is hard to use, and will require some
    tinkering before the desired result is obtained. The number of options for
    this filter depends on the number of output channels. An example how to
    downmix a six-channel file to two channels with this filter can be found
    in the examples section near the end.

    ``<n>``
        Number of output channels (1-8).
    ``<matrix>``
        A list of values ``[L00,L01,L02,...,L10,L11,L12,...,Ln0,Ln1,Ln2,...]``,
        where each element ``Lij`` means how much of input channel i is mixed
        into output channel j (range 0-1). So in principle you first have n
        numbers saying what to do with the first input channel, then n numbers
        that act on the second input channel etc. If you do not specify any
        numbers for some input channels, 0 is assumed.
        Note that the values are separated by ``,``, which is already used
        by the option parser to separate filters. This is why you must quote
        the value list with ``[...]`` or similar.

    .. admonition:: Examples

        ``mpv --af=pan=1:[0.5,0.5] media.avi``
            Would downmix from stereo to mono.

        ``mpv --af=pan=3:[1,0,0.5,0,1,0.5] media.avi``
            Would give 3 channel output leaving channels 0 and 1 intact, and mix
            channels 0 and 1 into output channel 2 (which could be sent to a
            subwoofer for example).

    .. note::

        If you just want to force remixing to a certain output channel layout,
        it is easier to use the ``format`` filter. For example,
        ``mpv '--af=format=channels=5.1' '--audio-channels=5.1'`` would always force
        remixing audio to 5.1 and output it like this.

    This filter supports the following ``af-command`` commands:

    ``set-matrix``
        Set the ``<matrix>`` argument dynamically. This can be used to change
        the mixing matrix at runtime, without reinitializing the entire filter
        chain.

``scaletempo[=option1:option2:...]``
    Scales audio tempo without altering pitch, optionally synced to playback
    speed (default).

    This works by playing 'stride' ms of audio at normal speed then consuming
    'stride*scale' ms of input audio. It pieces the strides together by
    blending 'overlap'% of stride with audio following the previous stride. It
    optionally performs a short statistical analysis on the next 'search' ms
    of audio to determine the best overlap position.

    ``scale=<amount>``
        Nominal amount to scale tempo. Scales this amount in addition to
        speed. (default: 1.0)
    ``stride=<amount>``
        Length in milliseconds to output each stride. Too high of a value will
        cause noticeable skips at high scale amounts and an echo at low scale
        amounts. Very low values will alter pitch. Increasing improves
        performance. (default: 60)
    ``overlap=<percent>``
        Percentage of stride to overlap. Decreasing improves performance.
        (default: .20)
    ``search=<amount>``
        Length in milliseconds to search for best overlap position. Decreasing
        improves performance greatly. On slow systems, you will probably want
        to set this very low. (default: 14)
    ``speed=<tempo|pitch|both|none>``
        Set response to speed change.

        tempo
             Scale tempo in sync with speed (default).
        pitch
             Reverses effect of filter. Scales pitch without altering tempo.
             Add this to your ``input.conf`` to step by musical semi-tones::

                [ multiply speed 0.9438743126816935
                ] multiply speed 1.059463094352953

             .. warning::

                Loses sync with video.
        both
            Scale both tempo and pitch.
        none
            Ignore speed changes.

    .. admonition:: Examples

        ``mpv --af=scaletempo --speed=1.2 media.ogg``
            Would play media at 1.2x normal speed, with audio at normal
            pitch. Changing playback speed would change audio tempo to match.

        ``mpv --af=scaletempo=scale=1.2:speed=none --speed=1.2 media.ogg``
            Would play media at 1.2x normal speed, with audio at normal
            pitch, but changing playback speed would have no effect on audio
            tempo.

        ``mpv --af=scaletempo=stride=30:overlap=.50:search=10 media.ogg``
            Would tweak the quality and performance parameters.

        ``mpv --af=scaletempo=scale=1.2:speed=pitch audio.ogg``
            Would play media at 1.2x normal speed, with audio at normal pitch.
            Changing playback speed would change pitch, leaving audio tempo at
            1.2x.

``rubberband``
    High quality pitch correction with librubberband. This can be used in place
    of ``scaletempo``, and will be used to adjust audio pitch when playing
    at speed different from normal. It can also be used to adjust audio pitch
    without changing playback speed.

    ``<pitch-scale>``
        Sets the pitch scaling factor. Frequencies are multiplied by this value.

    This filter has a number of additional sub-options. You can list them with
    ``mpv --af=rubberband=help``. This will also show the default values
    for each option. The options are not documented here, because they are
    merely passed to librubberband. Look at the librubberband documentation
    to learn what each option does:
    http://breakfastquay.com/rubberband/code-doc/classRubberBand_1_1RubberBandStretcher.html
    (The mapping of the mpv rubberband filter sub-option names and values to
    those of librubberband follows a simple pattern: ``"Option" + Name + Value``.)

    This filter supports the following ``af-command`` commands:

    ``set-pitch``
        Set the ``<pitch-scale>`` argument dynamically. This can be used to
        change the playback pitch at runtime. Note that speed is controlled
        using the standard ``speed`` property, not ``af-command``.

``lavfi=graph``
    Filter audio using FFmpeg's libavfilter.

    ``<graph>``
        Libavfilter graph. See ``lavfi`` video filter for details - the graph
        syntax is the same.

        .. warning::

            Don't forget to quote libavfilter graphs as described in the lavfi
            video filter section.

    ``o=<string>``
        AVOptions.
