af_atempo.c File Reference

tempo scaling audio filter – an implementation of WSOLA algorithm More...

#include <float.h>
#include "libavcodec/avfft.h"
#include "libavutil/avassert.h"
#include "libavutil/avstring.h"
#include "libavutil/channel_layout.h"
#include "libavutil/eval.h"
#include "libavutil/opt.h"
#include "libavutil/samplefmt.h"
#include "avfilter.h"
#include "audio.h"
#include "internal.h"

Classes
struct	AudioFragment
	A fragment of audio waveform. More...
struct	ATempoContext
	Filter state machine. More...

Macros
#define	OFFSET(x)   offsetof(ATempoContext, x)
#define	RE_MALLOC_OR_FAIL(field, field_size)
#define	yae_init_xdat(scalar_type, scalar_max)
	A helper macro for initializing complex data buffer with scalar data of a given type.
#define	yae_blend(scalar_type)
	A helper macro for blending the overlap region of previous and current audio fragment. More...

Typedefs
typedef struct AudioFragment	AudioFragment
	A fragment of audio waveform.
typedef struct ATempoContext	ATempoContext
	Filter state machine.

Enumerations
enum	FilterState {   YAE_LOAD_FRAGMENT, YAE_ADJUST_POSITION, YAE_RELOAD_FRAGMENT, YAE_OUTPUT_OVERLAP_ADD,   YAE_FLUSH_OUTPUT }
	Filter state machine states.

Functions
	AVFILTER_DEFINE_CLASS (atempo)

Variables
AVFilter	ff_af_atempo

Detailed Description

tempo scaling audio filter – an implementation of WSOLA algorithm

Based on MIT licensed yaeAudioTempoFilter.h and yaeAudioFragment.h from Apprentice Video player by Pavel Koshevoy. https://sourceforge.net/projects/apprenticevideo/

An explanation of SOLA algorithm is available at http://www.surina.net/article/time-and-pitch-scaling.html

WSOLA is very similar to SOLA, only one major difference exists between these algorithms. SOLA shifts audio fragments along the output stream, where as WSOLA shifts audio fragments along the input stream.

The advantage of WSOLA algorithm is that the overlap region size is always the same, therefore the blending function is constant and can be precomputed.

Macro Definition Documentation

RE_MALLOC_OR_FAIL

#define RE_MALLOC_OR_FAIL	(		field,
			field_size
	)

Value:

do {                                                        \
        av_freep(&field);                                       \
        field = av_malloc(field_size);                          \
        if (!field) {                                           \
            yae_release_buffers(atempo);                        \
            return AVERROR(ENOMEM);                             \
        }                                                       \
    } while (0)

yae_blend

#define yae_blend

(

scalar_type

)

Value:

do {                                                                \
        const scalar_type *aaa = (const scalar_type *)a;                \
        const scalar_type *bbb = (const scalar_type *)b;                \
                                                                        \
        scalar_type *out     = (scalar_type *)dst;                      \
        scalar_type *out_end = (scalar_type *)dst_end;                  \
        int64_t i;                                                      \
                                                                        \
        for (i = 0; i < overlap && out < out_end;                       \
             i++, atempo->position[1]++, wa++, wb++) {                  \
            float w0 = *wa;                                             \
            float w1 = *wb;                                             \
            int j;                                                      \
                                                                        \
            for (j = 0; j < atempo->channels;                           \
                 j++, aaa++, bbb++, out++) {                            \
                float t0 = (float)*aaa;                                 \
                float t1 = (float)*bbb;                                 \
                                                                        \
                *out =                                                  \
                    frag->position[0] + i < 0 ?                         \
                    *aaa :                                              \
                    (scalar_type)(t0 * w0 + t1 * w1);                   \
            }                                                           \
        }                                                               \
        dst = (uint8_t *)out;                                           \
    } while (0)

A helper macro for blending the overlap region of previous and current audio fragment.

Variable Documentation

ff_af_atempo

AVFilter ff_af_atempo

Initial value:

= {
    .name            = "atempo",
    .description     = NULL_IF_CONFIG_SMALL("Adjust audio tempo."),
    .init            = init,
    .uninit          = uninit,
    .query_formats   = query_formats,
    .process_command = process_command,
    .priv_size       = sizeof(ATempoContext),
    .priv_class      = &atempo_class,
    .inputs          = atempo_inputs,
    .outputs         = atempo_outputs,
}