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.
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.
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.
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.
Set the number of used channels. Default value is 0. This option is only used for special remapping.
Set the input sample rate. Default value is 0.
Set the output sample rate. Default value is 0.
Specify the input sample format. Must be an integer representing the
corresponding sample format specified in
‘libavutil/samplefmt.h’ header. Default value is -1
(corresponding to AV_SAMPLE_FMT_NONE
).
Specify the output sample format. Must be an integer representing the
corresponding sample format specified in
‘libavutil/samplefmt.h’ header. Default value is -1
(corresponding to AV_SAMPLE_FMT_NONE
).
Set the internal sample format. Default value is -1.
Set the input channel layout.
Set the output channel layout.
Set center mix level. It is a value expressed in deciBel, and must be inclusively included between -32 and +32.
Set surround mix level. It is a value expressed in deciBel, and must be inclusively included between -32 and +32.
Set LFE mix level.
Set rematrix volume. Default value is 1.0.
Set flags used by the converter. Default value is 0.
It supports the following individual flags:
force resampling
Set the dither scale. Default value is 1.
Set dither method. Default value is 0.
Supported values:
select rectangular dither
select triangular dither
select triangular dither with high pass
Set resampling filter size, default value is 16.
Set resampling phase shift, default value is 10, must be included between 0 and 30.
Use Linear Interpolation if set to 1, default value is 0.
Set cutoff frequency ratio. Must be a float value between 0 and 1, default value is 0.8.
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
.
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.
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.
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.
Select matrixed stereo encoding.
It accepts the following values:
select none
select Dolby
select Dolby Pro Logic II
Default value is none
.
Select resampling filter type. This only affects resampling operations.
It accepts the following values:
select cubic
select Blackman Nuttall Windowed Sinc
select Kaiser Windowed Sinc
Set Kaiser Window Beta value. Must be an integer included between 2 and 16, default value is 9.