Libavresample (lavr) is a library that handles audio resampling, sample format conversion and mixing. More...
Libavresample (lavr) is a library that handles audio resampling, sample format conversion and mixing.
Interaction with lavr is done through AVAudioResampleContext, which is allocated with avresample_alloc_context(). It is opaque, so all parameters must be set with the AVOptions API.
For example the following code will setup conversion from planar float sample format to interleaved signed 16-bit integer, downsampling from 48kHz to 44.1kHz and downmixing from 5.1 channels to stereo (using the default mixing matrix):
Once the context is initialized, it must be opened with avresample_open(). If you need to change the conversion parameters, you must close the context with avresample_close(), change the parameters as described above, then reopen it again.
The conversion itself is done by repeatedly calling avresample_convert(). Note that the samples may get buffered in two places in lavr. The first one is the output FIFO, where the samples end up if the output buffer is not large enough. The data stored in there may be retrieved at any time with avresample_read(). The second place is the resampling delay buffer, applicable only when resampling is done. The samples in it require more input before they can be processed. Their current amount is returned by avresample_get_delay(). At the end of conversion the resampling buffer can be flushed by calling avresample_convert() with NULL input.
The following code demonstrates the conversion loop assuming the parameters from above and caller-defined functions get_input() and handle_output():
When the conversion is finished and the FIFOs are flushed if required, the conversion context and everything associated with it must be freed with avresample_free().
Definition at line 103 of file avresample.h.
Referenced by audiogen(), avresample_build_matrix(), avresample_get_matrix(), avresample_open(), avresample_set_channel_mapping(), avresample_set_compensation(), avresample_set_matrix(), ff_audio_data_add_to_fifo(), ff_audio_data_alloc(), ff_audio_data_init(), ff_audio_data_realloc(), ff_audio_data_set_channels(), ff_audio_mix(), ff_audio_mix_get_matrix(), ff_audio_mix_set_matrix(), and main().
Mixing Coefficient Types.
16-bit 8.8 fixed-point
32-bit 17.15 fixed-point
floating-point
Definition at line 108 of file avresample.h.
Resampling Filter Types.
Cubic.
Blackman Nuttall Windowed Sinc.
Kaiser Windowed Sinc.
Definition at line 116 of file avresample.h.
Do not use dithering.
Rectangular Dither.
Triangular Dither.
Triangular Dither with High Pass.
Triangular Dither with Noise Shaping.
Number of dither types.
Not part of ABI.
Definition at line 122 of file avresample.h.
Get the AVClass for AVAudioResampleContext.
Can be used in combination with AV_OPT_SEARCH_FAKE_OBJ for examining options without allocating a context.
Definition at line 108 of file options.c.
Referenced by init(), opt_default(), and resample_child_class_next().
Allocate AVAudioResampleContext and set options.
Definition at line 94 of file options.c.
Referenced by config_output(), config_props(), and main().
Initialize AVAudioResampleContext.
Definition at line 35 of file utils.c.
Referenced by avresample_set_compensation(), config_output(), config_props(), and main().
Close AVAudioResampleContext.
This closes the context, but it does not change the parameters. The context can be reopened with avresample_open(). It does, however, clear the output FIFO and any remaining leftover samples in the resampling delay buffer. If there was a custom matrix being used, that is also cleared.
Definition at line 257 of file utils.c.
Referenced by avresample_free(), avresample_open(), avresample_set_compensation(), config_output(), main(), and uninit().
Free AVAudioResampleContext and associated AVOption values.
This also calls avresample_close() before freeing.
Definition at line 273 of file utils.c.
Referenced by config_output(), main(), and uninit().
Generate a channel mixing matrix.
This function is the one used internally by libavresample for building the default mixing matrix. It is made public just as a utility function for building custom matrices.
Definition at line 87 of file audio_mix_matrix.c.
Referenced by ff_audio_mix_alloc().
Get the current channel mixing matrix.
If no custom matrix has been previously set or the AVAudioResampleContext is not open, an error is returned.
Definition at line 498 of file utils.c.
Referenced by avresample_set_compensation().
Set channel mixing matrix.
Allows for setting a custom mixing matrix, overriding the default matrix generated internally during avresample_open(). This function can be called anytime on an allocated context, either before or after calling avresample_open(), as long as the channel layouts have been set. avresample_convert() always uses the current matrix. Calling avresample_close() on the context will clear the current matrix.
Definition at line 527 of file utils.c.
Referenced by avresample_set_compensation().
Set a customized input channel mapping.
This function can only be called when the allocated context is not open. Also, the input channel layout must have already been set.
Calling avresample_close() on the context will clear the channel mapping.
The map for each input channel specifies the channel index in the source to use for that particular channel, or -1 to mute the channel. Source channels can be duplicated by using the same index for multiple input channels.
Examples:
Reordering 5.1 AAC order (C,L,R,Ls,Rs,LFE) to Libav order (L,R,C,LFE,Ls,Rs): { 1, 2, 0, 5, 3, 4 }
Muting the 3rd channel in 4-channel input: { 0, 1, -1, 3 }
Duplicating the left channel of stereo input: { 0, 0 }
Set compensation for resampling.
This can be called anytime after avresample_open(). If resampling is not automatically enabled because of a sample rate conversion, the "force_resampling" option must have been set to 1 when opening the context in order to use resampling compensation.
Definition at line 247 of file resample.c.
Referenced by filter_frame().
Convert input samples and write them to the output FIFO.
The upper bound on the number of output samples is given by avresample_available() + (avresample_get_delay() + number of input samples) * output sample rate / input sample rate.
The output data can be NULL or have fewer allocated samples than required. In this case, any remaining samples not written to the output will be added to an internal FIFO buffer, to be returned at the next call to this function or to avresample_read().
If converting sample rate, there may be data remaining in the internal resampling delay buffer. avresample_get_delay() tells the number of remaining samples. To get this data as output, call avresample_convert() with NULL input.
At the end of the conversion process, there may be data remaining in the internal FIFO buffer. avresample_available() tells the number of remaining samples. To get this data as output, either call avresample_convert() with NULL input or call avresample_read().
Definition at line 325 of file utils.c.
Referenced by filter_frame(), main(), request_frame(), and write_to_fifo().
Return the number of samples currently in the resampling delay buffer.
When resampling, there may be a delay between the input and output. Any unconverted samples in each call are stored internally in a delay buffer. This function allows the user to determine the current number of samples in the delay buffer, which can be useful for synchronization.
Definition at line 463 of file resample.c.
Referenced by filter_frame(), get_delay(), main(), and request_frame().
Return the number of available samples in the output FIFO.
During conversion, if the user does not specify an output buffer or specifies an output buffer that is smaller than what is needed, remaining samples that are not written to the output are stored to an internal FIFO buffer. The samples in the FIFO can be read with avresample_read() or avresample_convert().
Definition at line 609 of file utils.c.
Referenced by filter_frame(), get_delay(), handle_trimming(), and main().
Read samples from the output FIFO.
During conversion, if the user does not specify an output buffer or specifies an output buffer that is smaller than what is needed, remaining samples that are not written to the output are stored to an internal FIFO buffer. This function can be used to read samples from that internal FIFO.
Definition at line 614 of file utils.c.
Referenced by filter_frame(), and handle_trimming().