Description
***********

The FFmpeg resampler provides an high-level interface to the libswresample library audio resampling utilities. In particular it allows to perform audio resampling, audio channel layout rematrixing, and convert audio format and packing layout.

Resampler Options
*****************

The audio resampler supports the following named options.

Options may be set by specifying -OPTION VALUE in the FFmpeg tools, or by setting the value explicitly in the SwrContext options or using the libavutil/opt.h API for programmatic use.

ich, in_channel_count
     Set the number of input channels. Default value is 0. Setting this value is not mandatory if the corresponding channel layout in_channel_layout is set.

och, out_channel_count
     Set the number of output channels. Default value is 0. Setting this value is not mandatory if the corresponding channel layout out_channel_layout is set.

uch, used_channel_count
     Set the number of used channels. Default value is 0. This option is only used for special remapping.

isr, in_sample_rate
     Set the input sample rate. Default value is 0.

osr, out_sample_rate
     Set the output sample rate. Default value is 0.

isf, in_sample_fmt
     Specify the input sample format. It is set by default to none.

osf, out_sample_fmt
     Specify the output sample format. It is set by default to none.

tsf, internal_sample_fmt
     Set the internal sample format. Default value is none.

icl, in_channel_layout
     Set the input channel layout.

ocl, out_channel_layout
     Set the output channel layout.

clev, center_mix_level
     Set center mix level. It is a value expressed in deciBel, and must be inclusively included between -32 and +32.

slev, surround_mix_level
     Set surround mix level. It is a value expressed in deciBel, and must be inclusively included between -32 and +32.

lfe_mix_evel
     Set LFE mix level.

rmvol, rematrix_volume
     Set rematrix volume. Default value is 1.0.

flags, swr_flags
     Set flags used by the converter. Default value is 0.

     It supports the following individual flags:

     res
          force resampling

dither_scale
     Set the dither scale. Default value is 1.

dither_method
     Set dither method. Default value is 0.

     Supported values:

     rectangular
          select rectangular dither

     triangular
          select triangular dither

     triangular_hp
          select triangular dither with high pass

filter_size
     Set resampling filter size, default value is 16.

phase_shift
     Set resampling phase shift, default value is 10, must be included between 0 and 30.

linear_interp
     Use Linear Interpolation if set to 1, default value is 0.

cutoff
     Set cutoff frequency ratio. Must be a float value between 0 and 1, default value is 0.8.

min_comp
     Set minimum difference between timestamps and audio data (in seconds) below which no timestamp compensation of either kind is applied. Default value is FLT_MAX.

min_hard_comp
     Set minimum difference between timestamps and audio data (in seconds) to trigger padding/trimming the data. Must be a non-negative double, default value is 0.1.

comp_duration
     Set duration (in seconds) over which data is stretched/squeezed to make it match the timestamps. Must be a non-negative double float value, default value is 1.0.

max_soft_comp
     Set maximum factor by which data is stretched/squeezed to make it match the timestamps. Must be a non-negative double float value, default value is 0.

matrix_encoding
     Select matrixed stereo encoding.

     It accepts the following values:

     none
          select none

     dolby
          select Dolby

     dplii
          select Dolby Pro Logic II

     Default value is none.

filter_type
     Select resampling filter type. This only affects resampling operations.

     It accepts the following values:

     cubic
          select cubic

     blackman_nuttall
          select Blackman Nuttall Windowed Sinc

     kaiser
          select Kaiser Windowed Sinc

kaiser_beta
     Set Kaiser Window Beta value. Must be an integer included between 2 and 16, default value is 9.

See Also
********

ffmpeg(1), ffplay(1), ffprobe(1), ffserver(1), libswresample(3)

     [file authors.texi not included]